Simulium venustum

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.

• Biogeographic Regions
• nearctic nearctic
• ethiopian ethiopian
• neotropical neotropical

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.

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

• 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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

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.

• Development - Life Cycle
• metamorphosis metamorphosis

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.

• Mating System
• polygynous polygynous

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.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous
• sperm-storing sperm-storing

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.

• 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.

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.

• Key Behaviors
• flies
• diurnal diurnal
• parasite parasite
• motile motile
• colonial colonial

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.

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.

• Communication Channels
• visual visual
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• infrared/heat infrared/heat
• chemical chemical

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.

• Primary Diet
• herbivore herbivore
  • nectarivore nectarivore

• Animal Foods
• blood
• aquatic crustaceans

• Plant Foods
• nectar
• pollen
• algae

• Other Foods
• detritus detritus

• Foraging Behavior
• filter-feeding filter-feeding

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 .

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.

• Ecosystem Impact
• pollinates
• parasite parasite

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.

• 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.

• Negative Impacts
• injures humans
  • bites or stings
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease

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.

Additional Links

Encyclopedia of Life

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.

References

Adler, P. 2003. Prevalence of the trichomycete fungus Harpella melusinae (Harpellales: Harpellaceae) in larval black flies (Diptera: Simuliidae) across a heterogeneous environment. Mycologia , 95(4): 577-583.

Azevedo, L. 2006. Spatial and Temporal Distribution of Blackflies (Diptera: Simuliidae) in the Itatiaia National Park, Brazil. Neotropical Entomology , 35(4): 542-550.

Bay, D., R. Harris, J. Robinson. 1999. Black Flies or Buffalo Gnats (Family: Simuliidae). Introduction to Veterinary Entomology , 1(9): 1-2. Accessed February 24, 2010 at http://entowww.tamu.edu/ .

Desser, S. 2002. Structural organization of the midgut musculature in black flies (Simulium spp.). NRC Research Press Web , 80(2): 910-917. Accessed February 25, 2010 at http://cjz.nrc.ca .

Ezenwa, A. 1974. Studies on Host-Parasite Relationships of Simuliidae with Mermithids and Microsporidans. Journal of Parasitology , 60(5): 809-813.

Hamada, N. 2009. Species Richness and Distribution of Blackflies (Diptera: Simuliidae) in the Chapada Diamantina Region, Bahia, Brazil. Neotropical Entomology , 38(3): 332-340.

Hansen, E. 1979. Laboratory Infection of Blackflies (Simuliidae) Midges (Chironomidae), By the Mosquito Mermithid, Romanomermis Culicivorax. Journal of Parasitology , 65(4): 613-615.

Landeiro, V. 2009. Species Richness and Distribution of Blackflies (Diptera: Simuliidae) in the Chapada Diamantina Region, Bahia, Brazil. Neotropical Entomology , 38(3): 332-339.

McCreadie, J., P. Adler. 1999. Parasites of larval black flies (Diptera: Simuliidae) and environmental factors associated with their distributions. Invertebrate Biology , 118(3): 310-318.

Pybus, M. 2001. Parasitic diseases of wild mammals . Ames, Iowa: Blackwell Publishing Company.

Sutcliffe, J. 1980. Bifurcate sensilla on the tarsi of female black flies, Simulium venustum (Diptera:Simuliidae): Contact chemosensilla adapted for olfaction. Journal of Morphology , 165(1): 1-11.

Trivinho-Strixino, S. 2006. Larval Description of Simulium (Notolepria) cuasiexiguum and Simulium (Chirostilbia) obesum and New Records of Black Fly Species (Diptera: Simuliidae) in the States of São Paulo and Minas Gerais, Brazil. Neotropical Entomology , 35(5): 698-704.

Upton, S. 2005. "TOPIC 45. Order: Diptera; suborder: Nematocera" (On-line). Animal Parasitology Course Lecture Notes. Accessed February 22, 2010 at http://www.k-state.edu/parasitology/classes/625arth45.html .

Wotton, R. 1978. Growth, respiration, and assimilation of blackfly larvae (Diptera: Simuliidae) in a lake-outlet in Finland. Oecologia , 33(3): 279-290.

2004. Guide to Aquatic Macroinvertebrates of the Upper Midwest . Minnesota: University of Minnesota.

2004. The Black Flies (Simuliidae) of North America . Ithaca, NY: Cornell University Press.

Illinois Department of Public Health. 2008. "Biting Flies" (On-line). Accessed February 20, 2010 at http://www.idph.state.il.us/envhealth/pcbitingflies.htm .

University of Florida IFAS Extension. 1998. "Black Flies, Simulium spp. (Insecta: Diptera: Simuliidae)" (On-line). University of Florida IFAS Extension. Accessed February 22, 2010 at http://edis.ifas.ufl.edu .

Ohio State University Extension. 2009. "Black Flies" (On-line). Ohio State University Extension Fact Sheet. Accessed February 22, 2010 at http://ohioline.osu.edu/hyg-fact/2000/2167.html .

University of Minnesota Extension Service. 2000. "Black Flies" (On-line). University of Minnesota Extension Service. Accessed February 24, 2010 at http://www.extension.umn.edu/yardandgarden/ygbriefs/e601blackflies.html#top .

University of New Hampshire Cooperative Extension. 2001. "Black Fly Fact Sheet" (On-line). University of New Hampshire Cooperative Extension. Accessed February 22, 2010 at http://www.ultimate.com/washington/wla/blackfly/ .

1975. Blackflies. Pp. 1-117 in Blackflies (Diptera: Simuliidae): A Problem Review and Evaluation . Vancouver, Canada: The University of Britsh Columbia.

2003. Dipteran predators of Simuliid blackflies: a worldwide review.. Medical Veterinary Entomology , 17(2): 115-132.

Wildpro Multimedia. 2010. "Invertebrate Species Summary Page" (On-line). Wildlife Information Network. Accessed February 24, 2010 at http://wildlife1.wildlifeinformation.org/s/0zAMand_Hexapod/Dipt_Simu_Simulium/Simulium_venustum.html .

2001. "Los Angeles County West Vector & Vector-Borne Disease Control District" (On-line image). Accessed February 21, 2010 at http://www.lawestvector.org/black_flies.htm .

2008. Mermithids (NEMATODA: MERMITHIDAE) Parasitizing Different Blackfly (DIPTERA: SIMULIIDAE) Populations in Quebec: Environmental Parameters Related to their Presence of Absence in the studied brooks. Journal of the American Mosquito Control Association , 24(3): 438-443.

2007. Pheromonal communication involved in courtship behavior in Diptera. The Journal of Insect Physiology , 53(11): 1089-1100.

1993. Phylogeny of Sibling Species of Simulium venustrum and S. verecundum (Diptera:Simuliidae) Based on Sequences of Mitochondrial 16s rRNA Gene. Molecular Phylogenetics and Evolution , 2(4): 293-303.

1917. Progressive Medicine: A Quarterly Digest of Advances, Discoveries and Improvements in the Medical and Surgical Sciences. Journal of the American Medical Association , 154(5): 1713.

2008. "River Blindness Onchocerciasis" (On-line). CDC. Accessed February 24, 2010 at http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/factsht_onchocerciasis.pdf .

1979. The Gonotrophic Cycle in Simulium Ochraceum. American Journal of Tropical Medicine , 28(2): 422-426.

2007. "The Importance of Size in the Dipteran Mating System" (On-line). Accessed March 10, 2010 at https://www.msu.edu/user/miller20/pala.htm .

2008. "The Merck Veterinary Manual" (On-line). Accessed February 19, 2010 at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/71702.htm .

1969. The Swarming and Mating Flight of Diptera. Annual Review of Entomology , 14(10): 271-298.

2000. "University of Minnesota Yard and Garden Entomology" (On-line). Black Flies. Accessed February 24, 2010 at http://www.extension.umn.edu/yardandgarden/ygbriefs/e601blackflies.html .

Soil & Water Conservation Society of Metro Halifax. 2006. "Zoobenthos of Freshwaters- An Introduction" (On-line). Accessed March 01, 2010 at http://www.chebucto.ns.ca/ccn/info/Science/SWCS/ZOOBENTH/BENTHOS/i.html .