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Black flies — always waiting for the next meal

Tin Mountain Nature Corner

May 27, 2010
Black flies are no bigger than six millimeters long, and on close inspection, their thorax is humped over their heads. They have compound eyes, two wings and the female mouthparts are sharp and serrated like a shark. There are more than 1,800 known black fly species distributed throughout the world. Forty species reside in New Hampshire, and according to the Extension Service at the University of New Hampshire, only two species consistently and abundantly bite humans. These are Prosimulium mixtum and Simulium venustum.

Black flies are an indicator species, i.e., they require clean, flowing water to survive, and the Mt. Washington Valley is fortunate to have numerous clean rivers, brooks and streams that support a healthy, productive crop of black flies.

Female black flies lay their eggs in running water, and once hatched, the larvae attach to rocks or aquatic vegetation using silk suctions and threads. The larvae are carnivores and have mouths with folding fans that expand while eating. Mature larva spin a triangular cocoon on the floor of the stream and pupate under water before ascending to the surface through a bubble of air, emerging as an adult black fly ready to mate and begin feeding. Because ice melts in running water before lakes, the black fly usually emerges before the mosquitoes.

Both male and female black flies feed on nectar of wildflowers and help in the pollination process, but only the female bites and draws a blood meal to nourish her eggs. Depending on species, females feed on livestock, wildlife, birds, humans, and certain cold blooded species. Swarms of flies in turn make up a good portion of the protein diet for trout, bats, birds, and turtles, as well as other wildlife. Unlike mosquitoes, black flies feed only during the day, but alas there is no relief since mosquitoes are active at night.

Next time you are bitten by a black fly, take it in stride; you are simply part of the continuum of life. s

Written by Donna Marie Dolan, TMCC PR/Communications Manager, ddolan@ tinmountain.org


•In New Hampshire there are two types of black fly life cycles. One overwinters in the egg stage, the second overwinters in the larval stage. The former hatches in spring when the water reaches 40 to 50 degrees, and the latter when it reaches 37 to 38 degrees.

•Black flies have four stages: eggs, larva, pupa and adult. All live in water except the adult.

•Gill filaments allow the larvae to take oxygen directly form the water.

•Some black fly species in Africa can range as far as 40 miles from one aquatic breeding site in search of their host.

•Black flies are attracted to carbon dioxide and dark colors.

•In tropical areas certain species of black flies can transmit river blindness.

•Black flies are scientifically classified in the Order Diptera.

• Black flies are most active between 9 and 11 a.m., and from 4 p.m. until the sun sets.

Some fun science terms

•Diptera means "two wings" (Greek di-two, plus ptero-wing). The usage dates back to Aristotle, who noted, correctly, that they were different from typical insects with four wings and that no two-winged insect had a stinger.

•Laciniae: in zoology, this is the pointed posterior of the maxilla (upper jaw) of an insect.

•A lotic ecosystem is the ecosystem of a river, stream or spring. Lotic refers to moving water. Black flies depend on lotic habitats.

•Syntrophy: cross-feeding, whereas one species lives off the products of another species.

Upcoming Tin Mountain Programs

Saturday, May 22 — Tin Mountain Herbarium Project I with noted botanist Paul Martin Brown, from 10 a.m. to 3 p.m. at the Nature Learning Center.

Thursday, May 27 — New Hampshire Bird Migration at 7 p.m. at the Nature Learning Center.

Varney Smith
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