Solenopsis invicta

Geographic Range

Red imported fire ants ( Solenopsis invicta ) are native to the Neotropical region of South America, including Argentina, Bolivia, Brazil, Paraguay, Peru, and Uruguay. These ants have been introduced to the Oriental, Australian, Neotropical, Palearctic, and Oceanic regions. Red imported fire ants are established in southern North America, as far north as the southern border of Virginia and southward through the Carolinas and Georgia to Key West, Florida. The are found in every state bordering the Gulf of Mexico (Florida, Alabama, Mississippi, Louisiana, and Texas). In Texas, these ants are concentrated around the eastern two-thirds of the state. Additionally, these ants have been found in the southern two-thirds of Arkansas and as far north as Marion County, Oklahoma. In Virginia, this species has been found as far north as Essex County. Fire ants have also been found in Graham County and Pinal County Arizona. In California, fire ants have been found in Los Angeles County and the low laying coastal areas immediately to the south of Los Angeles. In Mexico, populations occur in the tropical and subtropical areas of the country that receive adequate annual rainfall to sustain establishing colonies. The range extends along the eastern border of Mexico, spanning from the northern border with the United States, as far south as Jalapa, Tabasco; populations have extended as far west as the foothills of the Sierra Madre Mountains. In southeast Asia, red imported fire ants can be found in the southeastern third of China, the temperate regions of South Korea, the southern tip of Japan, and the majority of Thailand. Finally, these ants have established colonies in Ipswich and Brisbane, Queensland, Australia. These colonies are both disjunctive and rare.

• Biogeographic Regions
• palearctic palearctic
  • introduced introduced
• oriental oriental
  • introduced introduced
• neotropical neotropical
  • introduced introduced
  • native native
• australian australian
  • introduced introduced
• oceanic islands oceanic islands
  • introduced introduced

Habitat

Red imported fire ants inhabit a wide range of suitable habitats. Ideally, their habitat is in an area of freshly disturbed or loosened soil with direct exposure to sunlight, an annual rainfall of greater than 510mm, and a climate that does not sustain a temperature of lower than -12.3 °C. The optimal surface soil temperature range for foraging and reproduction of these ants is between 22 °C and 36 °C The breadth of environmental conditions which are ideal for these ants has allowed for colony establishment in temperate and tropical environments. Here, they have been observed in grasslands, forests, along waterways, and in scrub lands. The tendency of fire ants to establish in human-impacted environments has made them particularly well-suited for urban, suburban, and riparian settings. In regions where these ants are introduced, forested areas and areas of dense shrubbery are not easily colonized. In the non-native ranges, fire ants establish themselves in areas of human-caused disturbances, such as pastures, parks, golf courses, ditches, along roadways, and along infrastructure developments (e.g., power lines, pipelines, paths, garden beds). The strongest predictor for the establishment of new colonies is the disturbance of an area by human intervention. Another significant contributor to the likelihood of colonies being established in new locales is the lack of woody plants, and direct sunlight exposure on the soil surface. While no consensus has been reached on the elevation upper limitations of fire ants, there have been samples taken from established colonies from sea level upwards to 610 meters above sea level at the foothills of the Sierra Madre Mountains.

• Habitat Regions
• temperate temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• rainforest rainforest
• scrub forest scrub forest

• Other Habitat Features
• urban urban
• suburban suburban
• agricultural agricultural
• riparian riparian

Physical Description

Generally, red imported fire ants are brownish-red in color, with some variation in color as they age. It is not uncommon for fire ants to have an orange or yellow coloration. Sexually reproductive female elates are noted as having a darker coloration, with the only orange or reddish color being present in the head and mandibles. Males of this species are darkly colored, with no red or orange hue, and may have white markings on antennae. Fire ant workers are non-reproductive females, and are polymorphic. All fire ants exhibit bilateral symmetry and their lengths, mass, and anatomical ratios are highly variable. Factors that impact the size and shape of the workers are: order of hatching, age of the colony, nutritional availability to the colony and queen, and environmental conditions. Colonies that are raised in the laboratory setting will generally have smaller workers with little variation, where colonies in the wild will have a wider range of variation. In younger colonies, the initial brood of workers will have had only a minimum amount of nutrients to grow, so the initial set of workers are exceptionally small, and are called minims or nanitics. Minims are usually 2mm in length, which is strongly contrasted by a fully mature worker (majors) in a well-established colony that may reach 6mm in length. Fire ant eggs are 0.25-1.0mm in diameter, the larvae are 0.5-2.0mm in length depending on age, and in the pupae are 3mm to 6mm millimeters in length. Queen fire ants are primarily delineated from workers in the colony by their differential coloration and are sometimes slightly larger size, between three to seven millimeters . Weights have not been reported for individual fire ants. Differences in subspecies of fire ants are difficult to discern with the naked eye, and further differentiation between different castes of a colony is likewise difficult. For this reason, the various anatomical structures of the species are measured at the sub-millimeter scale with laboratory equipment. The largest species of fire ants are the bullet ants ( Paraponera claveta ), and the smallest species are the little fire ants ( Wasmannia auropunctata ). Differentiation between subspecies is also accomplished by the counting and descriptions of the dozens of facets of the exoskeletal structures of each subspecies. Due to the complex nature of making these determinations, obtaining a true identification of a subspecies in the field is impractical. Red imported fire ants are a venomous species, with stingers extending from end their thorax. To administer a sting, fire ants will latch onto the victim with their mandibles and utilize that leverage to drive the stinger into the victim. Once inserted, they will inject an oily alkaloid solution that is diluted with various protein complexes which can be unique to specific queens.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry
• polymorphic polymorphic
• venomous venomous

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

Fire ants start as a milky-white egg that is 0.25-1mm in diameter. Eggs, which are generally cared for by the nest’s workers, take 7-10 days to hatch. These eggs need to have their cleanliness and moisture maintained by workers during this period. When the eggs hatch the ants are in a larval form, approximately 0.5-2.0mm in length, have a grub-like appearance, and are blind and immobile. Larvae require constant tending, cleaning, and feeding by the colony. After this larval stage of 6-12 days, fire ants will pupate and undergo metamorphosis for 12-15 days. Pupae have a milky white appearance and change from a conical grub shape into a more angular ant form as they grow. Later in their development, black spots appear (which progress into eye). After the pupal stage, fire ants emerge underdeveloped. They are unable to move, see, or feed themselves, and are extremely fragile. These new ants require an additional 9-16 days before functioning independently within the colony. During their lifespan, fire ants will continue slow indeterminate growth. Worker ants will continue to grow throughout their life, and if a colony is healthy and large enough, will develop into a morphologically distinct member called a major. Majors are identifiable by their much larger heads and mandibles when compared to common colony workers. Non-major workers will increase in size as they age, and their roles in the colony will be determined by their respective ages. Sexual members of the colony will undergo the same growth cycle as workers, but will emerge from the pupae stage with wings. Sexual members will fill no function within the colony except reproduction. Virgin queens and sexual males take approximately 50-90 days from hatching to reach sexual maturity.

• Development - Life Cycle
• metamorphosis metamorphosis
• indeterminate growth indeterminate growth

Reproduction

Fire ants begin the mating process in the home nest. For months leading up to the mass reproductive event (called nuptial flights, or dispersal flights), reproductive females and reproductive males have been tended to by the workers in the colony. In all ant species, only some select females and all males become reproductive. These select females’ reproductive capability has been inhibited by pheromones produced by the colonies’ queen. Each reproductive member of the colony is distinguishable by a set of wings which only grow on sexual members of the colony. These members will perform no other function beyond reproduction within the colony. Colonies, depending on their genetic makeup and type of founding, will specialize in the production of one sex. Bhatkar (1991) found this mono-sex production is observed in 95.82% of reproductive colonies. In the late spring or early summer, colonies will initiate the reproductive process. The weather conditions ideal for reproduction are an ambient temperature of 25-35 °C, 60-80% relative humidity, and winds at or below 8kmph. In laboratory and field experiments, nuptial flights have been artificially initiated in colonies with an adequate population of reproductive individuals present. If weather variations occur while the nuptial flight is in progress, such as a drop in temperature or an increase in wind gusts, the reproductive individuals will retreat into the nest. In the case that the weather conditions remain ideal, reproductive colonies will release their reproductive individuals. Both reproductive males and reproductive females will take flight. It is during this time that observing reproduction becomes difficult and data on this process are limited. Queens will mate with only one male, and after mating is completed, will glide to the ground. Males that have successfully mated will also glide to the ground and die 2-96 hours after mating. Females will proceed to found a colony if they are a monogyne (single-queen colony type). If the queen is the polygyne type (multi-queen colonies), the newly mated queen may join other queens in the social founding of a new colony (called colony fission), or may return to their home colony to be adopted (reintegration). Fire ants are a eusocial species. Most ants hatched in the colony are sterile females and will perform the tasks of caring for the eggs, larvae, pupae, and newly emerged ants. As they age, workers will transition from caring for the young to maintaining the colonies’ sanitation and expansion. The oldest colony workers will become scouts and foragers, acquiring food sources for the colony.

• Mating System
• monogamous monogamous
• eusocial eusocial

Fire ants mate seasonally, with both males and females performing a nuptial flight between late spring and early summer. This reproductive flight is coordinated with the weather, where ideal temperature, humidity, and wind conditions trigger colonies with sexual members to initiate the flight. Insemination of the queen ant is performed mid-flight, with approximately 95% of females successfully mating with one male. Fire ants are semelparous, and the male ant dies soon after mating. If the queen was from a polygyne colony, she may land from the flight on the territory of her originating colony, and may be adopted back into the colony. If the newly mated queen originated from a monogyne colony, she glides away from the originating colony and forms an independent nest. During this glide process, queens will use the relative wind currents as a dispersal mechanism. Fire ant queens often glide toward reflective surfaces immediately following successful insemination. It’s possible that this mechanism increases the likelihood of a successful colony founding. Queens use rivers and streams to further the distance from themselves and a potentially hostile home-nest. Riparian, disturbed, and moist soils are ideal locations for nest establishment, but nest locals include retention ditches and ponds. Once the newly mated queen has landed, she will begin the process of creating a brooding chamber. In polygyne colonies, the queens create a new nest with other queens. Rarely, polygyne queens will return to their natal home nest. The process of multiple queens forming a new nest is known as colony fission. This may happen when the queen lands, or early in the founding of colonies when the first batch of workers (minims) are foraging for food. In monogyne colonies, a queen establishes a colony alone. The behavior, biology, ecology, and social organization of polygyne colonies differs considerably from monogyne colonies. These colonies are less aggressive, non-territorial, and highly cooperative. The new minims that are produced by multiple queens, despite being pheromonally and genetically distinct from their ‘step-sisters’, do not show aggression or defensiveness during the early founding of the colony. The new minims will also care for the brood of a non-genetically related queen. Almost invariably, the queens will be killed by workers of the colony, or other queens, until only one queen remains. After eight months, the mortality rate for fire ant queens is approximately 80%; after eight months in polygyne colonies, only one queen remains. The benefit of establishing a polygyne colony seems to be in the rapidity of colony growth and in mutual defense. While polygyne colonies are not defensive of their territory, they do still protect larvae and eggs. It is common for fire ant colonies to raid nearby nests for young, and the young that are taken are raised by the aggressor nest and function as workers despite their heritage. In polygyne colonies, it is much easier to defend from raiding colonies due to the increased number of minims compared to monogyne colonies. Colony efficiency is also a benefit to polygyne colonies. The most efficient possible scenario for fire ant colonies to grow is with 2-5 gynes, with efficiency significantly dropping off above 10 queens. In both the monogyne and polygyne colony founding scenarios, the reproductive cycle of individual queens remains the same. During mating, the queens receive a packet of approximately one-million sperm through internal mating, which the queens store for the remainder of their lives. After queens dig a new founding chamber, they will lay a clutch of approximately 10-20 milky-white eggs, each 0.25-1mm in diameter. Queens are iteroparous, and lay eggs in clutches initially. They will care for these eggs, cleaning them and keeping them moist during the 7-10 days before they hatch. When the eggs hatch, the ants are in a larval form, requiring constant tending, cleaning, and feeding by the queen. The larval stage is 6-12 days in length. The larva are blind, and look like grubs, and vary in size from 0.5-2mm, depending on colony health and size. After the larval stage, fire ants will pupate for 12-15 days. After the pupal stage, fire ants emerge underdeveloped, and require an addition 9-16 days before being able to function within the colony. Mature workers in the colony may live up to 8 months, but 60-150 days is more typical. When the first clutch of minims is mature, they will assume the task of caring for eggs, larvae, pupae, and new adult ants. In a mature and healthy colony, queens lay an average of 800 eggs per day, and the colony population can reach 500,000 workers. The average worker only lives for approximately 5 weeks. The queen can lay up to a thousand eggs a day when the colony is healthy, the weather is ideal, and food is plentiful. Female fire ants are iteroparous, and will often lay eggs year-round in warmer climates. In a single year, the queen may produce 4000-6000 sexual offspring (alates), and may continue this production for approximately seven years. Fire ant queens often specialize in which sex they produce. The alates that are produced serve no function other than to perform the nuptial flight. They do not participate in any colony activity during their time in the nest. They are cared for by workers in the colony. When it is time for a nuptial flight, the alates are encouraged out of the nest and into the air by workers of the colony. If the nest is in dense vegetation, workers from the colony will agitate the alates until they climb to the top of the vegetation. If the air temperature drops, or wind speed increases, the alates will retreat back into the nest until conditions are again ideal.

• Key Reproductive Features
• semelparous semelparous
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing

When queen fire ants lay their first clutch of eggs, they care for the eggs by ensuring that they are clean, intact, and properly moist. When the eggs hatch into larvae, they will clean and feed the larvae. Fire ant queens will also tend to the pupae, and clean newly emerged ants until they are able to function. After the first, founding ants of the colony are mature, they then assume all duties in the care of eggs, larvae, pupae, and new ants. Male fire ants die soon after mating, and have no involvement in caring for young.

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-hatching/birth
• post-independence association with parents

Lifespan/Longevity

The average lifespan of red imported fire ants is largely dependent on the size and health of the colony at the time a queen lays an egg, and what type of ant is hatched. Fire ant queens have an average longevity of 6.5 years, and workers may live between 91-375 days, depending on colony health at the time they hatch. Fire ants are not kept in captivity.

Behavior

The reproductive process for fire ants starts with a nuptial (or dispersal) flight where reproductive females and all males (collectively referred to as alates) fly from their home nests to copulate mid-flight, then glide towards the ground immediately following. The behavior of initiating the nuptial flight is governed by prevailing weather conditions, and the behavior of the colony’s workers. After insemination is complete, new queens will glide towards the ground in a way that shows an attraction towards reflective surfaces. This is believed to be a behavior that simultaneously increases the queen’s chance of success in establishing a founding colony, and allows for a longer range of travel. The in-flight behavior of fire ants is difficult to observe, and further research is needed. When founding new colonies, queens may develop a cooperative social dynamic with other queens to co-found a new nest. This cooperation is limited, as in time the queens (and workers within the colony) will kill other queens until one remains. Within the nest, younger fire ants maintain the nest cleanliness and brood health. This includes the cleaning and feeding of larvae, the removal of waste from the nest, and maintenance of various chambers. The tending ants in the nest will also relocate eggs and larvae to different chambers in the nest depending on the relative temperature, humidity, and light exposure. Workers in the nest also repeat pheromone signals from the queen, which can initiate whole-colony behaviors. These behaviors include relocation of the nest, a heightened defensive posture, or the attacking of an invading organism. Workers have also been observed killing queen ants in the case of colony fission in polygyne colonies. The exact nature or mechanism for selecting which queen to kill is unknown. During the early founding of colonies, foraging workers will discover other fire ant colonies and mark them using a pheromonal trail. The foraging worker will attract more workers via recruitment and raid the discovered colony. In this raid, the aggressing colony will kill resistors and take larvae and eggs from the marked colony. These larvae and eggs will be transplanted into the aggressor’s colony and raised as members there. In special cases of flooding or heavy rainfall, a mechanism is triggered wherein the colony rapidly moves to the surface to form a raft. The raft is formed out of workers latching on to each other in a three-dimensional lattice formation with the queen and brood in the center, and older workers on the outer edges. The combination of structure and mass that is formed as a result of this rafting behavior results in the restriction of water being able to move beyond the outermost layer of the raft. When the raft encounters a dry area, multiple ants latch on to the surface and evacuation of the mass begins. What the exact trigger for this behavior is and how it evolved is unknown. The foraging behavior of fire ants is much like other ant species. Foraging begins with tunnels that radiate from the main nest in many directions. Opening of these tunnels have been measured to be at 50-100cm intervals along the route. Fire ants will emerge from these tunnels and forage up to 100m from the entrance. Using primarily smell, the fire ants locate a food source. Using recruitment, fire ants will swarm and deplete the food source, and foraging will continue. Abdominal (or gastor) wagging has been observed in fire ants. This wagging is generally described as the up and down motion of the gastor in specific circumstances. These include when feeding, when performing recruitment, and within the colony. Fire ants also perform stridulation. This behavior has been seen during the digging of tunnels. While fire ants are digging, they will either pinch on to a particle of material, or press their mandibles into the material, and stridulate with their legs. This behavior may be used to loosen soil while digging, or to determine tunnel wall thickness. The behavior that most exemplifies fire ants is their stinging and biting behavior. This action is accomplished by an ant pinching down on the target with its mandibles, then leveraging its gastor into the target. The gastor of fire ants is tipped with a needle that delivers a painful and damaging venom into the target. There are multiple mechanisms that trigger this group stinging behavior, but not all mechanisms are known. The first, and most obvious mechanism is the alert (or alarm) pheromonal signal that occurs when a colony is under threat. This signal has the immediate effect of mobilizing all ants within a colony to become suddenly more motile. This leads to a swarm response on the target, which is then stung by any ant that it encounters. Fire ants areparticularly tenacious in their attack; there seems to be no known mechanism that stops fire ants from stinging apart from the death of the target, or the mechanical removal of the whole ant. Fire ants brumate during the winter months, remaining below the surface and stopping foraging activities. Colony size may reduce by 75% during these periods, and egg laying by the queen dramatically slows.

• Key Behaviors
• fossorial fossorial
• flies
• glides
• motile motile
• territorial territorial
• colonial colonial

Home Range

The home range of fire ants is largely dependent on multiple factors. The first major factor is the size of the colony. Smaller, younger fire ant colonies have fewer foraging workers and require fewer resources to maintain colony health. This results in a small home range with a short foraging reach. The second related factor to colony size and home range is the physical dimension of the colony itself. Fire ants are fossorial, and part of the foraging strategy is to burrow tunnels away from the nest with outlets to the surface every 50-100cm. If the colony is mature, and has a vast network of foraging tunnels, the home range is expanded. The third major factor in determining the home range of fire ants is the time of year. Colony size and resource requirements fluctuate with the seasons. During the early to middle summer, colony size is at its maximum, and the number of mature foragers is likewise high. This leads to a larger home range. In the winter months, the colony population and resource requirements decrease to up to one quarter of the colony summer population. Foraging may cease in cold weather, and the colony will subsist on stored resources. This reduces the home range to the physical dimensions of the main nest. The fourth major factor in home range size is the presence of colonies in proximity to another colony. There are established boundaries to the territory of fire ant colonies, and these borders can restrict home range. Warring between colonies is rare because of the maintenance of these boundaries, but conflict can be initiated when a particularly large and desirable resource is placed in the boundaries between two colony territories. In the field, scientists have marked fire ants leaving the nest for foraging and attempted to determine the exact distance a fire ant can be found from the point at which it emerged. These efforts have recorded ants over 100m from their nest entrances and casting of nests and foraging tunnels have shown that this is not an accurate measurement due to the extreme length of the foraging tunnels. The maximum length of these tunnels is unknown.

Communication and Perception

Ants communicate via chemical signals. The primary gland in fire ants used for communication is the Dufour’s gland, which is used in marking paths, marking territory, colony member identification, and signaling during recruitment behavior. The Dufour’s gland is also used in signaling perceived threats to the nest, and initiating fighting behaviors. Other glands in fire ants are used for signaling and communication, but are not as well understood. The stinger gland in fire ants is also used for chemical communication, including threat signaling, marking of threats for attack by colony members, and the marking of pupae by carers. Queen fire ants use stinger glands in marking larvae for removal from the queen’s chamber. The act of wagging the gastor is another method of communication. This is marked by a characteristic up and down wagging of the rear end of the individuals. This wagging is observed both inside and outside of the nest and has specific contexts for use. The first of these contexts is during the intake of particularly sugar or protein rich foods. The second context of this wagging behavior is inside of the nest and around other colony members. The exact nature of this wagging is unknown, but it has been hypothesized that wagging is a pleasure response to positive stimuli, and possibly an indication to other ants that the food source is particularly positive. Stridulation is another action performed by fire ants, and is characterized by the rubbing of hind legs against the body of the ant, or rubbing against another leg. This produces a small, low frequency vibration that is sensed by other ants that are near the stridulating individual. This behavior is seen primarily in tunneling ants, and there are two primary hypotheses to explain this behavior. First, perhaps the stridulation is used as a mechanical process to loosen soil particles during the tunneling process. Second, it is used as a tool to gauge the thickness of tunnel walls, and aids in tunnel path selection. The ability of fire ants to have fine visual acuity is a subject that is still a matter of debate. What is currently known is that fire ants do have color vision (to an unknown degree) and that they do show responses to color cues. It has widely been speculated that fire ants cannot sense red light (as part of a generalization about ants), but recent research by Carbaugh et al.(2020) has shown that these ants can sense and differentiate red light. The primary sensory and communication organs of fire ants are the antennae. These antennae are used as chemoreceptors, tactile sensors, and auditory/vibration sensors. These ants will use these antennae to ‘pat’ the ground in front of them for path finding and pheromone detection, or wave these antennae in the air to sense olfactory cues from the environment. Antennae are also used to sense food during foraging, and to follow the paths of scouts to food locations.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• scent marks scent marks
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

Fire ants, like other species of ants, are foragers. In the cololny, mature worker ants, the largest and oldest workers in the colony, assume the task of foraging once pupae care becomes less efficient due to their large size. Mature work ants primarily forage during the day, when surface temperatures are between 27 °C and 42 °C. The foraging range extends 10m beyond the ends of the longest foraging tunnels that are directly connected to the nests. These ants use olfactory receptors in their antennae to locate potential food sources and mark their trek to and from food sources using pheromones secreted from various glands, particularly Dufour’s gland. Once a food source has been identified, ants will transport the food back to the colony, following the pheromone trail back to the nest entrance. If the food is too heavy for the single ant to carry back to the colony, or if the food source is particularly sugary or abundant, fire ants will return to the nest and perform a recruitment. Recruitment is the act of soliciting other ants within the nest to follow the forager to a potentially high-value food source. The mechanisms of this recruitment process are still being studied, and are not well understood. This lack of understanding may be the result of communication vectors that are not easy for a researcher to observe. Though, if recruitment is successful, it is typical for the colony to have its strongest response to the recruitment efforts within 30 minutes of the arrival of the forager. A successful recruitment will result in a large quantity of ants following the pheromonal trail of the forager to the location of the food, and a team effort will ensue to relocate the food to the nest. The final observed phase of food acquisition is the transportation phase. In a recruitment scenario, these ants will collectively determine if the food source is suitable to transport to the nest. This determination is impacted by food size and weight, but the exact mechanism of this determination is unknown. If the food item is appropriate to transport, then the ants will relocate it to the colony. If the food is not suitable for transport, it will be broken down where it was discovered. Once food is relocated to the nest, the food is sorted through the complex structure of the nest to food holding areas for storage, pupae chambers, to the queen’s chamber, and among the workers. The exact mechanism of sorting food is unknown. Appropriate food sources for fire ants include nectar, sugar, sap, some animal tissues, insect tissues, grains, seeds, and human processed foodstuffs. If killing prey is necessary for fire ants, they will employ their venomous sting. This venom is lethal to most cells and causes the victim’s body to react with an inflammatory response. The sensation of the sting has been described as an intense burning sensation which eventually transforms into a typical itching sensation. This venom can be lethal to vertebrates, especially smaller ones, and is only lethal to humans in extreme quantities or when the victim has an extreme allergic response to the sting. This sting is the reason for the namesake of fire ants.

Food that has begun to decay, especially proteins and fats, will be thrown away by colonies in designated areas outside of the nest. This behavior is known as necrophoric behavior, and is highlighted as an extraordinary feature of these ants’ behavior. Fire ants have been observed consuming a wide variety of animals, including other insect. Types of insect debris found in the waste piles of fire ants includes flies (Order Diptera) in the adult, papae, larvae forms, beetles (Order Coleoptera) in all lifestage forms, crickets (Order Orthoptera), spiders (Order Aranae spp), wasp and bees (Order Hymenoptera), butterfly larvae (Order Lepidoptera), tree bugs (Order Hemiptera), termites (Order Ispotera), isopods (Order Isopoda), millipedes (Order Diplopoda), centipedes (Order Chilopoda), and thrips (Order Thysanoptera). Of these prey items, flies (58.5%) and isopods (21.7%) composed the majority of the insects found in waste piles. Fire ants have also been observed consuming deceased birds, livestock, reptiles, and the eggs of the eastern fence lizard ( Sceloporus undulatus ).

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • eats body fluids
  • insectivore insectivore
  • scavenger scavenger
• herbivore herbivore
  • frugivore frugivore
  • granivore granivore
  • nectarivore nectarivore
  • eats sap or other plant foods
• omnivore omnivore

• Animal Foods
• birds
• mammals
• amphibians
• reptiles
• body fluids
• carrion carrion
• insects
• terrestrial non-insect arthropods

• Plant Foods
• seeds, grains, and nuts
• fruit
• nectar

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Red imported fire ants in their introduced environments have no evolutionary predators. Predation of fire ants is largely coincidental and is the result of their predators’ generalization of feeding on all ants indiscriminately. Species that have been found to prey on mature fire ants include yellow garden spiders ( Argiope aurantia ), humped trashline orb weaver spiders ( Cyclosa turbinata ), pyramid ants ( Dorymyrmex insanus ), southern black widow spiders ( Latrodectus mactans ), and striped lynx spiders ( Oxyopes salticus ). The families of scarab beetles (Scarabaeidae), clown beetles (Histeridae), and leaf beetles (Chrysomelidae) have been found to prey on immature ant, larvae, and eggs. The family of seed bugs (Lygaeidae), and silverfish (order Zygentoma) also preys on immature ants inside the colony. Humans ( Homo sapiens ) kill these ants in every life stage to reduce their negative impacts on ecology, industry, and personal property.

Ecosystem Roles

Fire ants are predated by larger organisms like spiders, beetles and humans, while opportunistically preying on insects and larger vertebrates. Fire ants are hosts to many parasites, including the microsporidia Thelohania solenopsae and Vairimorpha invictae , the protozoa Mattesia geminata , and the fungi Beauveria bassiana , Metarhizium anisopliae , and fungi in the genus Aspergillis . Several species of insects use fire ants as hosts, including species of ant-decapitating flies in the genus Pseudacteon , some insects in order Strepsiptera, some species of parasitic wasps in the genus Orasema , nematodes Tetradonema solenopsis , and mites Pyemotes ventricosus .

Economic Importance for Humans: Positive

Red imported fire ants have no known positive economic impacts on humans.

Economic Importance for Humans: Negative

Red imported fire ants have had an extensive negative economic impact across the areas in which they were introduced. Specifically, fire ants have a negative impact on the agricultural industry, tourism, land management, and are a general pest to people living in areas impacted by their introduction. In agriculture, fire ants damage crops, injure or kill livestock, and injure farm workers. The painful stings of fire ants may also be fatal in some cases. Fire ants do directly impact the yield of crops. Adams et al. (1983) reported that areas of soybean ( Glycine max ) crop infested by fire ants produced 400 to 575kg less per hectare than non-infested areas. Urban farms in China reported a reduction of 10% to 80% in crop yields. In Hawaii, the economic impact on agriculture was estimated to be greater than $3,000,000 in 2006. The negative economic impact of fire ants is not solely due to direct damage to crops and livestock, but is also due to the necessity of prevention and treatment of infestations. Angulo et al. (2022) reported that the second highest cost associated with invasive ant species (particularly, red imported fire ants) was invasion management, costing an estimated $1.79 billion USD globally. In this same study, authors reported that a conservative estimate showed a total global economic impact of $51.93 billion USD.

• Negative Impacts
• injures humans
  • bites or stings
  • venomous venomous
• crop pest
• household pest

Conservation Status

Red imported fire ants are not listed on the IUCN red list, have no special status with the U.S. Fish & Wildlife Service, are not listed with CITES, and have no special status with the state of Michigan. There is currently no literature discussing fire ants as a threatened species, and no conservation efforts are currently being undertaken. These ants are globally invasive, and most efforts focus on eradication rather than preservation. Control or eradication of fire ants in the agricultural setting has been implemented in impacted areas. Chemical agents are the primary tool used in treating fire ants, with 19 agents considered effective in controlling and eliminating infestations. These agents include abamectin, acephate, boric acid, chlorpyrifos, pyrethrins, and rotenone. Biological controls, such as the introduction of parasitic flies, parasitic wasps, microsporangiaum, and other microorganisms have also been attempted. The use of both biological and chemical controls has not resulted in any permanent eradication of fire ants, and are primarily used in controlling populations and reducing impacts.

Other Comments

The introduction of red imported fire ants and black imported fire ants ( Solenopsis richteri ) into non-native ecosystems has allowed both species to flourish globally. Where both species co-occur in the United States, hybridization has been documented. These 'hybridization zones' extend through central Alabama, central Mississippi, western central Georgia, and southwest Virginia. These hybridized ants exhibit distinct morphologies, and have both adaptive and manipulative traits that emerge as a result of hybridization. Hybridized ants are generally less successful in rapid and aggressive colonization when compared to their parental species. As invasive ant ranges expand, the future of hybrid species and hybrid zones is unknown.

Additional Links

Encyclopedia of Life

Contributors

Nicholas Beach (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Adams, C., W. Banks, C. Lofgren, B. Smittle, D. Harlan. 1983. Impact of the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae), on the growth and yield of soybeans. Journal of Economic Entomology , 76/5: 1129-1132.

Allen, C., D. Epperson, A. Garmestani. 2004. Red imported fire ant impacts on wildlife: A decade of research. The American Midland Naturalist , 152/1: 88-103.

Angulo, E., B. Hoffmann, L. Ballesteros-Majia, A. Taheri, P. Balzani, A. Bang, D. Renault, M. Cordonnier, C. Bellard, C. Diagne, D. Ahmed, Y. Watari, F. Courchamp. 2022. Economic costs of invasive alien ants worldwide. Biological Invasions , 24/1: 2041-2060.

Asano, E., D. Cassill. 2011. Impact of worker longevity and other endogenous factors on colony size in the fire ant, Solenopsis invicta. Insectes Sociaux , 58: 551-557.

Bhatkar, A. 1991. Reproductive strategies of the fire ant. Pp. 138-149 in Applied Myrmecology: A World Perspective . Boca Raton, Fl: CRC Press.

Buren, W. 1972. Revisionary studies on the taxonomy of the imported fire ants. Journal of the Georgia Entomological Society , 7/1: 1-26.

Calcaterra, L., J. Livore, A. Delgado, J. Briano. 2008. Ecological dominance of the red imported fire ant, Solenopsis invicta, in its native range. Oecologia , 156: 411-421.

Carbaugh, J., R. Renthal, S. Vinson, R. Medina. 2020. Color discrimination and preference in the fire ant Solenopsis invicta Buren. Insectes Sociaux , 67: 167-178.

Cassill, D., K. Ford, L. Huynh, D. Shiffman, S. Vinson. 2016. A study on abdominal wagging in the fire ant, Solenopsis invicta, with speculation on its meaning. Journal of Bioeconomics , 18: 159-167.

Chan, K., B. Geunard. 2019. Ecological and socio-economic impacts of the red import fire ant, Solenopsis invicta (Hymenoptera: Formicidae), on urban agricultural ecosystems. Urban Ecosystems , 23/1: 1-12.

Chen, S., D. Fangyu, M. Hao, D. Jiang. 2020. Mapping the potential global distribution of red imported fire ant (Solenopsis invicta Buren) based on a machine learning method. Sustainability , 12/23: 10182. Accessed February 02, 2025 at https://doi.org/10.3390/su122310182 .

Global Invasive Species Database, 2025. "Solenopsis invicta" (On-line). Accessed March 26, 2025 at https://www.iucngisd.org/gisd/species.php?sc=77 .

Gunawardana, D. 2014. "Solenopsis invicta (red imported fire ant)" (On-line). CABI Digital Library. Accessed February 02, 2025 at https://doi.org/10.1079/cabicompendium.50569 .

Gutrich, J., E. VanGelder, L. Loope. 2007. Potential economic impact of introduction and spread of the red imported fire ant, Solenopsis invicta, in Hawaii. Environmental Science & Policy , 10/7-8: 685-696.

Haight, K. 2008. Ontogeny of the defensive stinging behavior of the fire ant, Solenopsis invicta. Journal of Insect Behavior , 21: 147-152.

Howard, D., W. Tschinkel. 1976. Aspects of necrophoric behavior in the red imported fire ant, Solenopsis invicta. Behavior , 56/1-2: 157-180.

Porter, S., W. Tschinkel. 1993. Fire ant thermal preferences: Behavioral control of growth and metabolism. Behavioral Ecology and Sociobiology , 32/5: 321-329.

Purdue University, 2024. "Survey Status of Red imported fire ant - Solenopsis invicta (2024)" (On-line). Center for Environmental and Research Information Systems (CERIS). Accessed February 07, 2025 at https://pesttracker.org/map.php?code=ISASAZA .

Rauth, S., S. Vinson. 2006. Colony wide behavioral contexts of stridulation in imported fire ants (Solenopsis invicta Buren). Journal of Insect Behavior , 19: 293-304.

Shoemaker, D., K. Ross, M. Arnold. 1996. Genetic structure and evolution of a fire ant hybrid zone. Evolution , 50/5: 1958-1976.

Steele, C., J. King, E. Boughton, D. Jenkins. 2020. Distribution of the red imported fire ant Solenopsis invicta (Hymenoptera: Formicidae) in central Florida pastures. Environmental Entomology , 49/4: 956-962.

Texas A&M University - Agricultural Communications, 2003. "Discovery may help in war against fire ants" (On-line). Accessed March 18, 2025 at www.sciencedaily.com/releases/2003/08/030811070436.htm .

Thawley, C., T. Langkilde. 2016. Invasive fire ant (Solenopsis invicta) predation of eastern fence lizard (Sceloporus undulatus) eggs. Journal of Herpetology , 50/2: 284-288.

Todd, R. 2025. "Hybrid fire ants continue to spread on Southwest Virginia" (On-line). Radio IQ. Accessed March 28, 2025 at https://www.wvtf.org/news/2025-03-21/hybrid-fire-ants-continue-to-spread-in-southwest-virginia .

Trager, J. 1991. A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae: Myrmicinae). Journal of the New York Entomological Society , 99/2: 141-198.

Tschinkel, W., S. Porter. 1988. The efficiency of sperm use in queens of the fire ant Solenopsis invicta . Annals of the Entomological Society of America , 81/5: 777-781.

Tschinkel, W., J. King. 2008. Experimental evidence that human impacts drive fire ant invasions and ecological change. Proceedings of the National Academy of Sciences of the United States of America , 105/51: 20339-20343.

Tschinkel, W. 1987. Colony growth and the ontogeny of worker polymorphism in the fire ant, Solenopsis invicta. Behavioral Ecology and Sociobiology , 22/2: 103-115.

Tschinkel, W. 2011. The organization of foraging in the fire ant, Solenopsis invicta. Journal of Insect Sciences , 11/1: #26. Accessed February 07, 2025 at https://doi.org/10.1673/031.011.0126 .

Tschinkel, W. 1998. The reproductive biology of fire ant societies. BioScience , 48/8: 593-605.

Turner, K., M. Conner, J. Beasley. 2021. Effects of red imported fire ant (Solenopsis invicta) control on carrion use by vertebrate scavengers. Food Webs , 29: e00212. Accessed February 02, 2025 at https://doi.org/10.1016/j.fooweb.2021.e00212 .

Vinson, S. 1997. Insect life: Invasion of the red imported fire ant (Hymenoptera: Formicidae). American Entomologist , 43/1: 23-39.

Vogt, J., R. Grantham, E. Corbett, S. Rice, R. Wright. 2002. Dietary habits of Solenopsis invicta (Hymenoptera: Formicidae) in four Oklahoma habitats. Environmental Entomology , 31/1: 47-53.

Wilson, E. 1962. Chemical communication among workers of the fire and Solenopsis saevissima (Fr. Smith) 2. An information analysis of the odour trail. Animal Behavior , 10/1-2: 148-158.

Yijuan, X., L. Yongyue, Z. Ling, L. Guangwen. 2007. Foraging behavior and recruitment of red imported fire ant Solenopsis invicta Buren in typical habitats of south China. Acta Ecologica Sinica , 27/3: 855-861.

Texas A&M AgriLife Extension. Managing Red Imported Fire Ants in Agriculture. B-6076. Texas A&M University Systems: AgriLife Extension. 1998. Accessed March 24, 2025 at https://ant-pests.extension.org/wp-content/uploads/2019/09/1998.ManagingIFAinAgric.B6076.pdf .

Texas A&M AgriLife Extension. Potential biological control agents for the red imported fire ant. ENTO-008. Texas A&M University Systems: AgriLife Extension. 2014.