Black Fly Larvae

Scientific Name: Simuliidae

Number Of Species/distribution
Simuliidae is a family of black flies containing about 1,750 species worldwide.
  • There are approximately 255 species in North America, with the greatest abundance in the northern regions.
  • They can even be found in the Arctic.
Diet/FeedingBlack fly larvae are classified as part of the feeding group "collectors/filterers".
  • They have a special 'brush-like' mouthpart that collects tiny organisms and organic matter out of the water that flows through it, acting as a sieve or filter.
  • As adults, the females of many species require a special diet for proper egg maturation during reproduction.
  • Females that are blood-feeders can be very aggressive, and are often considered pests to both humans and other mammals.
  • Furthermore, when feeding on blood, adult females can also transmit blood and skin parasites between mammals, including humans.
  • Not all adults that feed on blood target humans; only a few species attack humans, and this usually occurs when more suitable hosts are not present.
Black fly
  Habitat
Black fly larvae thrive in water with moderate to fast currents, and attach themselves to solid, usually smooth, substrates such as rocks, vegetation, and logs;
  • Black fly larvae require these swift currents in order to filter and collect enough food.
  • The larvae tend to stay attached to the substrate in fast-flowing waters by producing a silk thread from their mouths and using it to form sticky pads that adhere to the substrate surface.
  • The larvae have tiny hooks on the tips of their abdomens that they use to attach to these silk pads. Thus, a fairly clean substrate is needed to allow the larvae to stick their silk pads to it successfully.
  • Lake and pond outlets tend to make very productive habitats for black fly larvae because of the high level of organic material in the water.
  • The pupae are more likely to be found in the downstream sides of substrates such as on rocks, or closer to the base of aquatic vegetation where the current is slightly slower.

Lifecycle
Black flies can live from a few weeks to a few months. They undergo complete metamorphosis, passing through 4 different life stages: Egg  to Larvae to Pupa to Adult.

Eggs
  • Eggs are usually deposited in shallow, fast-running water within streams and rivers, often on submerged objects, such as rocks, leaves, and aquatic vegetation.
  • The eggs may also be scattered along the surface of the water.
  • Female black flies deposit approximately 150 to 500 creamy-white eggs, which usually develop over a period of four to five days.
  • They become darker as development progresses.
  • When water temperatures reach 70 degrees F, the eggs will be ready to hatch.
  • Eggs that are deposited in autumn do not hatch until the water warms the following spring.
  • For some species, the egg stage is the resistant stage of the life cycle; some can withstand drought and hatch when conditions are more favourable.
Larvae
  • After hatching, the young larvae attach themselves to submerged objects such as rocks.
  • In favourable conditions, the black fly larvae will remain at the hatching site.
  • If not, they will use a silk thread to drift downstream to sites with better conditions.
  • The larval stage of the life cycle can vary in length depending on the water temperature and other environmental conditions.
  • The larval stage can persist for anywhere from several weeks, when temperatures are warmer, to six or seven months, when overwintering occurs.
  • Black fly larvae typically pass through seven developmental stages, called instars.
  • Early instars have shorter durations than later ones.
  • When the larva reaches its final instar, it will spin itself a cocoon out of silk, forming a pupa.
  • The growth rate of black fly larvae depends greatly on the quality and abundance of food, and on water temperature.
Pupae
  • Pupation occurs within a cocoon that is open at one end.
  • The length of this stage varies depending on the temperature of the water, but generally lasts from four to seven days.
Adults
  • Adult black flies emerge from their pupal cocoon form by expanding their wings, which causes them to float to the surface in an air bubble.
  • The adult can then fly to a resting spot, where it waits for its outer layer (called a cuticle) to harden.
  • Adult black flies may be ready to mate shortly upon emergence from the pupal form.
  • Depending on the species, mating can occur during flight or while landed, and the female will need a meal of blood before or after laying her eggs.
  • Whether a blood-meal is needed depends on the species of black fly.
Role in Food Chain
Black flies play a significant role in ecosystems with flowing water.
  • They feed by filtering dissolved organic matter, making it available to other organisms within the food chain. This is known as 'nutrient cycling'.
Interesting Facts
  • Black flies are attracted to mammals because of the carbon dioxide and moisture that we exhale, and by our perspiration, perfumes, and dark colours.
  • The larval and pupal stages cannot swim; they crawl around the substrate in a motion similar to caterpillars.
  • Adult black flies often emerge at the same time in huge numbers, especially in temperate climates. These mass emergences can cause damage to livestock, as there are so many females seeking blood at the same time.
  • In some regions of the world, adult black flies can carry diseases such as river blindness, although this is not a problem in North America.

Sources
Black Flies.info (2010). Information. Available here.Bug Guide (2010). Family Simuliidae - Black Flies. Available here.
DMI International Corporation (2003). LaMotte Aquatic Macroinvertebrate Insect Identification Flashcards.
Guide to Aquatic Insects of the Upper Mid-west (2004). Diptera. Avaiable here.
Iowa State University Entomology (2010). Family Simuliidae - Black Flies. Available here.
Murray Darling Freshwater Research Centre (2006). Simuliidae Simulinae. Available here.
Ohio State University (2010). Black Flies. Available here.
Soil & Water Conservation Society of Metro Halifax (2004). Family Simuliidae. Available here.

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