Solenopsis molesta

Geographic Range

Thief ants ( Solenopsis molesta ) are native to the Nearctic region. They can be found across the United States, although they are most common in the eastern half of the country. They have been reported as far south as the middle of Mexico, although they are probably rare in that region.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Thief ants typically live in fields and meadows, although nests can be abundant in urban and suburban areas. They can live in turfgrass habitats, including golf courses and lawns, as well as grassy areas in cities, such as on the medians of major roads. They can also be found in agricultural fields. Nests are built in the ground, either in the open or under rocks. Nest openings are often a distance from the nest itself, with many underground tunnels and small chambers packed with solid walls. Thief ants can also build nests within homes, in basements, under baseboards, or in building foundations.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

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

Physical Description

Thief ants are small two-petiole ants. Workers are monomorphic; they are pale yellow and 1.5 to 1.8 mm in length. They have ten-jointed antennae, with a large, elongate antennal club. Queens are larger, at 4 to 5 mm in length. They are the same shade of yellow, with a darker brown color on their head, prothorax, and in between their abdominal segments. They have eleven-jointed antennae, with the same antennal club. Before mating, they have two pairs of hyaline wings, after mating, the queens lose their wings. Males are also larger than workers, though smaller than queens, at 3.5 to 3.6 mm in length. Their legs and antennae are yellow, while their body is brown. Eggs are pearly white, and become clear just before hatching. They are elliptical and 0.25 mm in length. Larvae are white, and covered in double-hooked hairs. Their posterior end is large, while their anterior end is smaller and tapered. Their body is curved, although the curvature decreases as the larva grows. Worker and reproductive pupae are not enclosed in cocoons and can be distinguished by their body size, worker pupae are the smallest, and queen pupae are the largest. All types are white during the early stages, and later change to the adult coloration.

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

• Sexual Dimorphism
• sexes colored or patterned differently

Development

Thief ants are holometabolous and undergo complete metamorphosis. Eggs hatch after 16 to 28 days. Larvae develop through several instars, while being tended and fed by workers. Larval stages last for about 21 days; the last instars, also called semi-pupae, last 2 to 11 days. Larvae present in the nest when temperatures drop, overwinter, and subsequently have a longer development time. The pupal stage lasts 13 to 27 day, after which, the callow stage, where the ant resembles an adult but is helpless and lacks pigments, lasts 2 or 3 days. It then becomes a fully-functioning adult. Workers have a minimum development time of 52 days, from egg to adulthood.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Mating takes place during a nuptial flight, which includes hundreds to tens of thousands of males and females. These flights occur during the afternoon, from about 4 to 6 pm, typically during the latter half of summer, from July to September. They mate in air. Some females even carry workers during the flight; these workers likely join the queen in forming a new colony. After mating, when the males and females have separated, females move to a new colony, and males die shortly afterward.

• Mating System
• eusocial eusocial

After mating, queens find new colonies. Immediately after being released from the male, females tend to fly aimlessly in big swooping paths. They find a suitable macrohabitat, such as a lawn or field, then search for microhabitats, such as a grass stem, a clump of earth, or a leaf to shelter under. They crawl beneath the object and stay there. Most queens begin their colony without workers, and their first batch of eggs develops into workers. However, some queens carry workers during the nuptial flight, which become the workers in the new colony. Queens lay eggs 3 days after mating, and may lay as many as 105 eggs in a single day. Most colonies have a single queen, although some have multiple, one nest in particular had 26 queens.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing
• delayed fertilization delayed fertilization

Similar to other ant species, worker thief ants exhibit significant parental investment and provide general care for all stages of the brood. Workers feed larvae via trophallaxis; regurgitating food and transferring it mouth to mouth. Workers help remove the meconium from larvae, which is a large mass voided from the alimentary tract just before molting into pupae. They also help remove the pupal skin when pupae molt into adults. After developing into adults, they enter a callow stage, where adults are weak and helpless, during this time, workers provide aid and carry them as needed. Once they have fully developed into adults, the ants join the colony and brood care stops. When queens form new colonies, they often do not have workers. In these instances, queens care for their young themselves. In addition to providing provisioning in the eggs, queens also produce trophic eggs to feed the larvae.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

In laboratory established colonies, queen mortality has been high; most queens generally do not survive more than two months. This high mortality rate is likely due to their small size and their propensity for desiccation. In natural habitats, queens likely live over a year. Males die shortly after mating, living only a few days to weeks as adults. Workers likely live a few months.

Behavior

Thief ants get their common name due to their habit of nesting in, or near other ant's nests, and stealing broods. They are very stealthy; partially due to their small size, they can easily remain undetected. Thief ants are not particularly aggressive towards other ant species, and tend to completely avoid or run away from other species. This defensive behavior is likely one of the reasons they are such successful brood thieves. Their nests are connected to the nests they rob by galleries that are too small for the other ant species, but large enough for the tiny worker thief ants to move freely between. Thief ants typically have small colonies, with several hundred to a couple thousand workers. Thief ants are aggressive to conspecifics from distant nests. Workers are monomorphic, and there are no worker castes. All tasks are done by workers, and much of their activity is subterranean. Most foraging takes place in the afternoon, when temperatures are warmest, but they also forage throughout the day and night if temperatures are warm enough.

• Key Behaviors
• terricolous
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• colonial colonial

Home Range

Home range is likely restricted to the area surrounding their nest, as well as any nearby nests from which they can steal.

Communication and Perception

When thief ants first come into contact with other ants, whether it is a nest mate or another species, they use their antennae to antennate the other individual. The antennae detect odors and chemicals that would identify a nest mate. Thief ants from distant nests are aggressive towards one another, suggesting that the identifying chemicals are relatively nest-specific. Their antennae are also used to detect odors and chemicals in the environment, and as a tactical method of perception. Thief ants can release a repellent from their poison gland that is long-lasting and very effective when thieving from other nests. It prevents the other ants from tending and protecting their brood, allowing thief ants to steal the brood without concern. When invading red imported fire ant's nests, thief ants remain undetected, this is potentially by mimicking their colony odors, allowing thief ants to sneak in and move about without drawing attention.

• Communication Channels
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Thief ants are omnivorous. They prey on a large variety of insect eggs and larvae, through subterranean foraging. The broods of other species are a significant portion of their diet, as they steal from nests. They also feed on vegetables, seeds, fruits, and honeydew, and even scavenge dead insects. Populations in urban and suburban environments are opportunistic, and eat human-produced foods including meats, breads, sweets, animal fat, and dairy products. Thief ants are also sometimes called 'grease ants', as they are commonly seen eating grease.

• Primary Diet
• omnivore omnivore

• Animal Foods
• insects

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

Predation

Recorded predators of thief ants include spiders , Texas horned lizards , skink species, and other species of ants including Crematogaster lineolata and soldier ants . To defend themselves, thief ants discharge defensive chemicals from their venom glands. Once the venom is released, these ants are typically more defensive than aggressive, and are more likely to run away from a threat than fight.

Ecosystem Roles

Their nests are often found in close proximity to nests of many other ant species. Thief ants sneak in to other nests and steal broods. One species they have regular interactions with are red imported fire ants . Thief ants can remain undetected in red imported fire ants' nests when they sneak in to rob a brood, and can effectively destroy a small colony of 30 to 60 workers, as they also prey on workers and queens. Red imported fire ants may avoid nesting in areas with a high density of thief ants. Unlike many other native ant species, thief ants seem to be relatively unaffected by invasive ant species, and can nest in invaded areas, while many other ant species cannot. In addition to nesting near red imported fire ants' nests, thief ants can also nest in areas colonized by Argentine ants , which normally displace all native ant populations. The ability of thief ants to co-exist may be attributed to their subterranean habits and foraging, as well as foraging at different times of the day, allowing them to avoid most interaction with invasive species. Thief ants farm a few species of honeydew-producing insects. In exchange for eating honeydew, the ants protect the insects from predators and parasitoids. These species include scale insects of genus Dactylopius , and aphids including Geoica squamosa , Aphis seteriae , Aphis middletoni , Antonina nortoni , Anuraphis maidiradicis , and Smynthurodes betae . Ectoparasitic mites of genus Hypoaspis have been found on workers, queens, and males. Thief ants may also be an intermediate host of poultry tapeworms , as they may carry tapeworm segments into their nests.

Economic Importance for Humans: Positive

Thief ants are a natural enemy of many pest species, providing a natural control method. These species include southern masked chafers and Japanese beetles , which are turfgrass pests, and can destroy large areas of grass in suburban and urban areas, incurring high costs of reseeding and resodding. Thief ants eat the eggs and larvae of these and other white grub species. They also feed on many agricultural pests, including black cutworms , all stages of maize billbugs , larvae of stalk borers , larvae of Hessian flies , pupae of corn-ear worms , and larvae of white-marked Tussock moths . However, since thief ants can be household and agricultural pests, they are not a particularly effective method of controlling pest populations outside of natural predation. Thief ants can also invade and destroy small colonies of red imported fire ants . Red imported fire ants are an invasive species that can be household pests and inflict painful stings, and thief ants appear to be an effective natural control on small colonies.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Thief ants caused crop damage in the early 1900's, especially to sorghum crops, typically by feeding on and destroying seeds. As late as 1959, they were referred to as the most harmful insect to sorghum, though there is very little mention of crop damage in the literature since then. While they may not currently be a significant agricultural pest, this species does have the potential to act as a crop pest. Additionally, by tending and protecting several species of honeydew-producing insects that can be agricultural pests, they can cause further damage to crops. Thief ants can nest in homes and other buildings, and often invade during warm weather. They can nest in cracks and crevices, under floorboards, in basements, and in the interior of walls. Due to their small size, they are difficult to keep out, and can easily slip in spaces to feed on food stored in pantries and kitchens. Thief ants are considered one of the "Dirty 22" pest species by the United States Food and Drug Administration. The "Dirty 22" is a list of the most common pests contributing to the spreading of foodborne pathogens. Several of their genes have been studied and analyzed to use as a method of identifying contaminants in food samples. Pesticides used for red imported fire ants are also often very effective on thief ants as well, and can curb infestations. However, it is important to note that some of the reports in literature about thief ants' status as household pests may be inaccurate due to mistakenly identifying pharaoh ants . Pharaoh ants are a much more significant nuisance than thief ants. Additionally, thief ants may be an intermediate host of poultry tapeworms , which can cause economic loss in poultry yields.

• Negative Impacts
• injures humans
  • carries human disease
• crop pest
• causes or carries domestic animal disease causes or carries domestic animal disease
• household pest

Conservation Status

Thief ants have no special conservation status.

Other Comments

In addition to the common name thief ants, they are also known as grease ants or sugar ants.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Texas State University.

References

Burkhardt, C. 1959. Increasing sorghum stands in field test by controlling thief ants and other insect pests. Journal of Economic Entomology , 52/3: 365-368.

DuBois, B., M. DuBois. 1994. Colony founding by queens of Solenopsis molesta ( Hymenoptera : Formicidae ). Entomological News , 105/2: 61-68.

Grundmann, A., B. Peterson. 1953. House infesting ants in Salt Lake City, Utah. Journal of the Kansas Entomological Society , 26/2: 59-60.

Jones, T., M. Blum, H. Fales. 1979. Synthesis of unsymmetrical 2,5-di-normal-alkylpyrrolidines - 2-Hexyl-5-pentylpyrrolidine from the thief ants Solenopsis molesta , Solenopsis texanas , and its homologs. Tetrahedron Letters , 12: 1031-1034.

Landis, J. 1967. Attendance of Smynthurodes betae ( Homoptera : Aphididae ) by Solenopsis molesta and Tetramorium caespitum ( Hymentopera : Formicidae ). Annals of the Entomological Society of America , 60/3: 707.

McColloch, J., W. Hayes. 1916. A preliminary report on the life economy of Solenopsis molesta Say. Journal of Economic Entomology , 9: 23-38.

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