Simulium venustum

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Geographic Range

Simulium venustum is typically found in northern latitudes including: tropical climates, northern temperate regions, and subarctic areas such as the Arctic Circle. This wide range of locations includes several continents most notably North America, South America, and Africa. (Azevedo, 2006; Hamada, 2009; Pybus, 2001; "Black Flies", 2000)

Habitat

Simulium venustum lives near areas of moving water such as streams, rivers, and brooks. This species lives in freshwater areas with a minimal amount of pollution and good air circulation because oxygen is needed for the immature stages to develop properly. Simulium venustum lives by water sources of low to neutral pH, usually in clear or very light colored water. They are very sensitive to chemicals and will not breed or lay eggs around contaminated sources. Black flies, as they are commonly called, are most active at temperatures above fifty degrees Fahrenheit. ("University of Minnesota Yard and Garden Entomology", 2000; Azevedo, 2006; Hamada, 2009; "Black Fly Fact Sheet", 2001; Wotton, 1978)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Simulium venustum measures from 1 to 6 millimeters in length with an average of about 3.2 millimeters. They have a wingspan that ranges from 3 to 9 millimeters. Although the common name is “black flies,” these insects are not always black. In fact, S. venustum is often gray, light tan, or even yellow. The thorax of both sexes of adult flies is well developed, along with an evolutionary progression of the scutum. This advancement is the reason that black flies have a hump-like appearance and head that is anatomically lower than in other Diptera. Males have a larger hump on the back of their thorax compared to females. The maxillary palps are divided into 5 segments and are longer than the stylet. A common feature of S. venustum is a white-banded tibia. Their wings are without ornamentation and do not have scales or hairs. Heavy veins line the edges of the anterior side of the wings. Simulium venustum possess short antennae with eleven small segments. This species features large round compound eyes in both males and females. In females, the compound eyes are dichoptic, which means separated on top of the head. This is contrary to males, who are holoptic, eyes are not differentiated, and touch at the middle line on top of the head. The thorax bulges outward and has sheen to it with light colored spotting on the abdomen. The abdomen is composed of 9 segments; the terminal 3 contain the genitalia. The female possesses one spermatheca, so that sperm can be stored and used to fertilize eggs. Often, S. venustum have a scutum that is adorned with horizontal stripes. Females have long and serrated stylets that are armed with four teeth which pierce their host during a blood meal. Males have simpler mouthparts with a straight stylet that is used for feeding on the nectar of plants. (Upton, 2005; "Blackflies", 1975; "The Black Flies (Simuliidae) of North America", 2004; "Black Flies", 2009; "Black Fly Fact Sheet", 2001)

  • Sexual Dimorphism
  • male larger
  • Range length
    1 to 6 mm
    0.04 to 0.24 in
  • Average length
    3.2 mm
    0.13 in
  • Range wingspan
    3 to 9 mm
    0.12 to 0.35 in

Development

Diptera, or true flies, develop in a holometabolous manner. This type of development is a four-stage process: egg, larva, pupa, and adult. Holometabolous development differs from some other metamorphosis process because the larva’s appearance greatly diverges from the adult. Hatching of the eggs can take between 5 to 30 days, depending on the temperature. These eggs change from white to a dark black right before they hatch. Egg length varies from 0.1 to 0.4 mm. Winter is usually spent in the first stage of development, the egg stage. Larvae develop just below slow moving water. Development of larvae has a very wide range for duration, from 10 days to 10 weeks. The larvae are without wings, have non-segmented legs, and need to live in a wet environment. This is because larvae and pupae development are somewhat temperature dependent. Larvae are a light brown color, and in the final instar a brown enclosed cocoon is spun onto a solid object such as a rock or log. This cocoon is shaped like a sailboat or basket. Pupation occurs within the cocoon, and 4 to 5 days later an adult emerges. The pupation stage can from 3 to 5 weeks depending on the temperature of the water. The colder the water, the slower the process. Development of the wings, segmentation of the legs, antennae, and compound eyes happens in the pupal stage. Though found in tropical and subtropical areas, breeding is slowed due to hot temperatures leading to increased risk of pupae drying out before transitioning to adulthood. ("Mermithids (NEMATODA: MERMITHIDAE) Parasitizing Different Blackfly (DIPTERA: SIMULIIDAE) Populations in Quebec: Environmental Parameters Related to their Presence of Absence in the studied brooks", 2008; Desser, 2002; Hamada, 2009; "Zoobenthos of Freshwaters- An Introduction", 2006; "Black Flies, Simulium spp. (Insecta: Diptera: Simuliidae)", 1998; "Black Flies", 2000; Wotton, 1978)

Reproduction

Simulium venustum have mating habits that are frequently seen in the Simuliidae family. Males usually have multiple female mates. The female mating patterns however, are not well studied. Mating occurs shortly after the first adult flight. The larger females are more attractive to males, which is hypothesized to be because they see these females as more fertile and capable of producing healthy offspring. Males hold females tightly with their legs during the in-flight mating process. Females are observed flying into swarms, and proceed to mate with a male while in the air. The male and female, while in the process of mating, begin by flying upwards from the swarm and then descend towards the ground. ("The Importance of Size in the Dipteran Mating System", 2007; "The Merck Veterinary Manual", 2008; "The Swarming and Mating Flight of Diptera", 1969)

The holometabolous cycle has four stages reproduction: egg, larva, pupa, and adult. First, female Simulium venustum need to search out a host for a blood meal. They anchor the proboscis on the host with hooks that are attached to the labrum. Mandibles pierce the skin with a the jagged edges and flies will feed for 4 to 5 minutes by lapping up pooled blood. After attaining the blood meal, females are ready to lay eggs. Simulium venustum deposits between 150 to 500 white eggs on an object that is in or near the water. A complete life cycle takes from 6 to 15 weeks and has between 1 and 6 generations. ("The Importance of Size in the Dipteran Mating System", 2007; "The Merck Veterinary Manual", 2008; Adler, 2003; Azevedo, 2006; Desser, 2002; "Black Flies", 2009; "Zoobenthos of Freshwaters- An Introduction", 2006)

  • Breeding interval
    Simulium venustum are capable of breeding more frequently during the warmer months.
  • Breeding season
    Simulium venustum breed from May to September, with greatest numbers in June and July.
  • Range eggs per season
    150 to 500
  • Average eggs per season
    350

Females are the dominant caretakers for the offspring of Simulium venustum. They prepare by obtaining the nutrients that they need from a blood meal from a host. This blood meal is necessary for the eggs to mature into healthy adults. Simulium venustum females scout out safe places to lay their eggs. This process can consume a lot of energy because females may need to fly up to 40 kilometers to a water source. (Upton, 2005; "The Black Flies (Simuliidae) of North America", 2004; "University of Minnesota Yard and Garden Entomology", 2000; Adler, 2003; Bay, et al., 1999; Hansen, 1979; Landeiro, 2009; "Black Flies", 2009)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Simulium venustum adults live an average of 3 to 5 weeks. They are temporary parasites that take advantage of a wide range of hosts to use for nutrients and protection. Larvae are dependent on water in order to develop into adults and without a flowing water source, larvae will die within 24 hours. ("University of Minnesota Yard and Garden Entomology", 2000; Adler, 2003; Azevedo, 2006; "Black Fly Fact Sheet", 2001)

  • Typical lifespan
    Status: wild
    21 to 35 days
  • Average lifespan
    Status: wild
    26 days

Behavior

Black flies are capable of biting during morning and early afternoon hours, typically in shaded or partially shaded regions. They are attracted to dark colors such as black and navy blue. Simulium venustum are attracted to the carbon dioxide that the host exhales. Simulium venustum follows the trail of carbon dioxide and surveys the host to see if the host is suitable. As flies get within a few centimeters of the host, the fly senses heat expended by the host and lands on the area of exposed skin. Humans are great targets of female black flies because they exhale more carbon dioxide than any other host. Simulium venustum most commonly lives and attacks in swarms. The swarming technique is harmful for cattle, often by exsanguination. Black flies are very motile and able to fly long distances due to strong flight muscles. (Upton, 2005; "Dipteran predators of Simuliid blackflies: a worldwide review.", 2003; "University of Minnesota Yard and Garden Entomology", 2000; Hansen, 1979; Landeiro, 2009)

  • Range territory size
    10 to 40 km^2

Home Range

Simulium venustum is capable of living within a wide area around a main water source. They are commonly known for living about 10 kilometers from the water in which the female laid her eggs. Black flies have the capability of flying up to 40 kilometers to reach a suitable water source to lay eggs. ("Guide to Aquatic Macroinvertebrates of the Upper Midwest", 2004; Desser, 2002; Landeiro, 2009; "Black Flies", 2009; Sutcliffe, 1980; "Black Flies, Simulium spp. (Insecta: Diptera: Simuliidae)", 1998; "Black Fly Fact Sheet", 2001)

Communication and Perception

Communication between male and female flies is mostly for the purpose of mating. Males of the order Diptera produce pheromones as a mating technique in order to attract females. Advanced movements of the legs and wings of males, attract females who fly to the location of the potential mate. Females of the family Simuliidae tend to utilize a pheromone that marks a flower and prevents other flies from feeding from their energy source. Sensing of carbon dioxide to find a host is accomplished from the sensilla of the antennae. This type of process is an action and response type of reaction where the host exhales and the black fly picks up on the trail of carbon dioxide and finds a host. Heat waves produced from the host's movements allow female S. venustum to sense and follow a potential blood meal from 10 to 15 inches away. Also, when the fly is within about two inches of the host, the compound eye is used for establishing the location of the host. Flies are also attracted to perfumes, strong odors, and perspiration. ("Blackflies", 1975; "Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences", 1917; "The Merck Veterinary Manual", 2008; Azevedo, 2006; Ezenwa, 1974; Trivinho-Strixino, 2006; Wotton, 1978)

Food Habits

Nectar is a food source for both sexes of Simulium venustum. Females require nectar for development of the ovaries and for energy to search for a potential blood meal. Female black flies require blood for egg maturation. Like some species of Diptera, including Simulium vittatum, Simulium venustum can secrete an enzyme during feeding that stops the hosts' blood from clotting and allows the fly to feed for a longer period of time. Larvae feed on small protozoa and crustaceans, or even algae. The larvae have a unique brush system on their mouthparts that resembles a fan. This method is used in order to filter food particles from the water and break up large particles into edible ones. Many of these particles are epithelial cells or excreted waste products of other organisms. ("Blackflies", 1975; Adler, 2003; Desser, 2002; Ezenwa, 1974; "Black Flies", 2009; "Black Flies", 2000)

  • Animal Foods
  • blood
  • aquatic crustaceans
  • Plant Foods
  • nectar
  • pollen
  • algae

Predation

Simulium venustum are a major food source for many fish, dragonfly larvae, and crustaceans. There are many predators of Simulium venustum in the phylum Arthropoda including: Coleoptera, Odonata, Plecoptera, and Trichoptera. (Upton, 2005; "Los Angeles County West Vector & Vector-Borne Disease Control District", 2001; Hansen, 1979; "Black Flies, Simulium spp. (Insecta: Diptera: Simuliidae)", 1998; "Invertebrate Species Summary Page", 2010)

Ecosystem Roles

Although very disruptive to most communities, there are a few benefits that Simulium venustum provide. Fungi of the class Trichomycetes are symbionts of black flies, and common in the larvae. Paramoebidium are found in the hindgut of S. venustum. Larvae are also hosts to a variety of nematodes, including Mermithidae, and the chytrid fungus. Throughout Africa, many larvae have a phoretic relationship with small crabs. Parasitic larva of the family Mermithidae pierce the fly's body and coil inside the abdomen of the host. These worms can be seen in the fly's body under the microscope and have a looped appearance. Mermithids destroy the host upon exiting, and usually wait until the adult stage when the most damage is created. Many protozoan species cause infections to the body by eating active spores. (Upton, 2005; Adler, 2003; Azevedo, 2006)

Species Used as Host
Commensal/Parasitic Species
  • chytrid fungus
  • Mermithidae
  • Paramoebidium
  • Trichomycetes

Economic Importance for Humans: Positive

Although black flies are pests to most species, they perform a few tasks that benefit the environment. These organisms play a key function in recycling of organisms in the water because of the filtering system that the larvae use. The detritus is reprocessed, not to mention the added benefit of cleaning the water source. The presence of Simulium venustum indicates a clean water supply, due to their sensitivity to chemicals in the water. This indirect benefit is especially helpful in areas in Africa where clean water is not always available. Black flies pollinate wildflowers as they drink the nectar. ("Phylogeny of Sibling Species of Simulium venustrum and S. verecundum (Diptera:Simuliidae) Based on Sequences of Mitochondrial 16s rRNA Gene", 1993; "Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences", 1917; "Black Flies", 2009; "Black Flies", 2000)

  • Positive Impacts
  • pollinates crops

Economic Importance for Humans: Negative

Simulium venustum are vicious biters of humans, mules, cattle, hogs, turkeys, chickens, sheep, and domesticated dogs and cats. The flies bite areas of exposed skin such as: the arms, legs, ears, or mouth. On humans, it is common to have bites directly below the waistline. Multiple bites on the host can result in anemia, anaphylactic shock, or even death. Soon after being inflicted, the bite looks red and very swollen, which lasts a few days. Then the bite shrinks in size, but becomes itchy. The itching reaction and pain from the bite is caused from the salivary glands of Simulium venustum that contains toxins and anti-coagulants. Black flies are the vectors for many pathogens that affect vertebrates including: heartworms, onchocerciasis, Mansonella ozzardi infection and leucocytozoonosis.

Onchocerciasis is the second leading cause of blindness worldwide. Onchocerciasis is caused by Onchocerca volvulus, a nematode. The adult O. volvulus live in the subcutaneous tissue and produce larvae that gravitate towards the skin and eyes. Since black flies breed near flowing water, onchoceriasis is also called river blindness. This infection is found throughout South America, Central America, and Africa.

Mansonella ozzardi, a nematode, is found in South America, Central America, and the Caribbean. M. ozzardi causes filariasis, especially in the lymph vessels that can lead to elephantiasis.

Heartworm is caused by Dirofilaria immitis that belongs to the phylum Nematoda. The symptoms of this infection are: shortness of breath, coughing, weight loss, and loss of appetite. Heartworm is common with domesticated animals and can be fatal without treatment.

Leucocytozoonosis is caused by a protozoan leucocytozoon parasites that infect the blood and is then transmitted by S. venustum. Leucocytozoonosis usually infects turkeys and chickens. This causes an economic problem for countries that rely on these animals as a form of income and a source of food. ("Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences", 1917; "River Blindness Onchocerciasis", 2008; "The Gonotrophic Cycle in Simulium Ochraceum", 1979; Upton, 2005; "Blackflies", 1975; "Los Angeles County West Vector & Vector-Borne Disease Control District", 2001; "Mermithids (NEMATODA: MERMITHIDAE) Parasitizing Different Blackfly (DIPTERA: SIMULIIDAE) Populations in Quebec: Environmental Parameters Related to their Presence of Absence in the studied brooks", 2008; "Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences", 1917; "River Blindness Onchocerciasis", 2008; "The Gonotrophic Cycle in Simulium Ochraceum", 1979; "The Merck Veterinary Manual", 2008; Adler, 2003; Azevedo, 2006; "Biting Flies", 2008; Pybus, 2001; "Zoobenthos of Freshwaters- An Introduction", 2006; Sutcliffe, 1980; "Black Flies", 2000; "Black Fly Fact Sheet", 2001)

Conservation Status

Black flies breed and lay eggs near clean water sources and avoid areas with even moderate amounts of pollution. With the conscious environmental Green movement that has taken effect throughout the world, Simulium venustum are as prosperous as ever. They are not endangered in the communities in which they live; in fact, populations are continuously growing. Advanced recycling systems and better sanitation practices have ultimately lead to an increase in S. venustum. There are many control measures used to protect cattle and humans from bites. Non-toxic larvacides are used to kill larva and developing larva in the water. Humans can wear light colored clothing and long sleeves and pants, in order to prevent a lot of skin from being exposed. Other measures include: citronella candles, chemical repellants such as DEET, or fogging. (Upton, 2005; "Guide to Aquatic Macroinvertebrates of the Upper Midwest", 2004; "Pheromonal communication involved in courtship behavior in Diptera", 2007; "Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences", 1917; "The Black Flies (Simuliidae) of North America", 2004; McCreadie and Adler, 1999; "Black Flies", 2000)

Contributors

Caitlin McMillan (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

nectarivore

an animal that mainly eats nectar from flowers

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

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