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Simulium damnosum

By Kensey Amaya

Geographic Range

Simulium damnosum is widespread in throughout western, eastern, central, and southern Africa. (Strickland, 1991)

Habitat

Egg and larval development take place in fast-flowing white-water rivers in tropical and temperate regions of Africa. Adult S. damnosum flies inhabit both forests and savannahs in the tropical and temperate regions. (Biggam and Wright, 1964; Crosskey, 1995)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Deposited eggs from of the species Simulium damnosum are about 0.20 mm in length; mature larvae can reach a length of 5.5 to 9.5 mm and are worm-like. Larvae have three distinct features: A pair of cephalic fans on the head used for feeding, two psudopods know as prolegs or "false feet" which consists of a series of 30 to 50 rows of hooks, and a thoracic proleg located on the underside immediately behind the head and is used in locomotion. The abdominal proleg at the hind end of the body is used to secure the larvae to a substrate when it is stationary. Adult S. damnosum can reach a length of 3 to 4 mm. The body is composed of a head, a thorax that is humped in relation to the rest of the body, and an abdomen. Both sexes have a conspicuous white band on each of the hind tarsi. Males tend to be black, while females tend to be grayer. In addition, males have a reflective silvery mark on their abdomen that aids in recognition by females during mating. The mandibles in females are larger and have a row or teeth that are used for cutting and bloodletting. (Crosskey, 1995; Goodwin and Duggan, 1972)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • sexes shaped differently
  • Range length
    3 to 4 mm
    0.12 to 0.16 in

Development

Simulium damnosum eggs hatch within a few days and larvae attach to objects in the water using their abdominal proleg. The larval stage has seven instars, which can take between seven to fourteen days to complete. Following the larval stage is a pupal stage that takes two to six days to complete, after which the S. damnosum fly emerges to the surface in a protective bubble of air and lives for about three or four weeks as an adult out of water. (Crosskey, 1995; Strickland, 1991)

Reproduction

Copulation is believed to only occur once in females. (Crosskey, 1995; Strickland, 1991)

After copulation sperm are usually stored in the spermatheca where it is used later for fertilization once the eggs have become mature. After the eggs are fertilized they are oviposited in large masses consisting of about 700 eggs, in some cases deposits of 1100 eggs have been observed. The eggs are deposited in fast flowing water just below the surface on vegetation or other protruding objects. (Crosskey, 1995; Strickland, 1991)

  • Range eggs per season
    700 to 1100

Behavior

Simulium damnosum flies exhibit mostly a solitary life style with no organized social structure. However, female S. damnosum flies have been shown to oviposit their eggs on the same substrate as other females; this is due to pheromones that are released by other egg-laying females. Swarms of male flies in pre-copulatory behavior have been observed but they are extremely rare and are not considered a common behavior in the species. Simulium damnosum have been observed to migrate up to 550 km from their original location, and when resting they prefer to do so on trees at heights above 12 meters. (Crosskey, 1995; McCall, et al., 1997)

Food Habits

Larval S. damnosum show little selectivity, feeding on dissolved organic matter, bacteria, diatoms, algae, and animal matter. Both male and female adult S. damnosum feed on nectar, in particular Rhus natalensis bushes, but only the female feeds on blood. Blood feeding by the female occurs using her serrated mandibles, creating a "mini-wound" where blood begins to ooze out. Feeding often occurs in the morning, in the evening, and on cloudy days when there is decreased light intensity and high humidity. (Crosskey, 1995)

  • Plant Foods
  • nectar
  • algae

Economic Importance for Humans: Positive

There is no known economic benefit derived from this species.

Economic Importance for Humans: Negative

Simulium damnosum is the primary vector for the Onchocerca volvulus filarial worm, or river blindness parasite that affects humans in Africa. Transmission to humans occurs during feeding of S. damnosum, when the filarial worm travels from the proboscis of the fly into the bleeding wound. River blindness is not fatal, but does cause disfigurement and blindness; approximately 18 million people are infected globally, about 99% of which are in Africa. (Crosskey, 1995)

  • Negative Impacts
  • injures humans
    • bites or stings
    • carries human disease

Conservation Status

Other Comments

Since 1973, the World Health Organization (WHO) has led the Onchocerciasis Control Program (OCP) in West Africa. The programs goal is to control the population of Simulium damnosum through the use of insecticide in the savanna regions of West Africa where the Onchcercisis volvulus filarial worm causes the most social and economic damage. (Crosskey, 1995)

Contributors

Sara Diamond (editor), Animal Diversity Web.

Kensey Amaya (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.

Glossary

Ethiopian

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

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.

carnivore

an animal that mainly eats meat

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

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

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.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

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

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sanguivore

an animal that mainly eats blood

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.

tropical

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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Biggam, S., F. Wright. 1964. Tropical Diseases. Baltimore, MD: The Williams and Wilkins Company.

Crosskey, R. 1995. The Natural History of Blackflies. West Sussex, England: John Wiley and Sons Ltd..

Goodwin, L., A. Duggan. 1972. A New Tropical Hygiene and Human Biology. London, England: George Allen and Unwin LTD.

McCall, P., M. Wilson, B. Dueben, B. de Clare Bronsvoort, R. Heath. 1997. Similarity in oviposition aggregation pheromone composition within the Simulium damnosum (Dipter: Simuliidae) species complex. Bulletin of Entomological Research, 87: 609-616.

Peters, W., H. Gilles. 1995. Color Atlas of Tropical Medicine and Parasitology. Barcelona, Spain: Mosby-Wolfe.

Strickland, T. 1991. Hunter's Tropical Medicine. Philidelphia, PA: W.B. Saunders Company.

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