Diptera is one of the most important, and least discussed, orders of insects for fly fishermen. With species in that live in almost any environment--terrestrial, aquatic, and parasitic--an angler can encounter a member of this order in almost any water habitat. Some species are annoying, like mosquitoes, black flies, and no-see-ums, but others, like chironomid and midges, are important food sources for trout.

Often called true flies because they have only a single pair of wings, Diptera larvae have no tails or legs and look like a segmented tube. In its pupae form, the head, thorax, and wing pads are clumped together. As adults, only one pair of wings develop, a second undeveloped pair form small knoblike appendages call halteres that act as stabilizers during flight. Aquatic midges have long been recognized as an important food source, but terrestrial Diptera have mostly been overlooked. Common land-born Diptera like deerfly and housefly are taken by trout occasionally but members of the family Bibionidae, land on the water with enough regularity and in sufficient numbers to cause selective feeding in some locales.

Bibio, also known as Hawthorne Flies and Heather Flies in the U.K. and March Flies in the U.S., are usually 3/8 to 1/2 inches long and have shiny black or dark brown bodies with a red or yellow mark around their collar, depending on the species. Though short, their antennae is thick and pronounced and extends from beneath the eyes. Bibio legs are relatively long compared to their body and have large "thorns" or "combs" extending from them. The thorax of the insect is somewhat robust and bulging but the abdominal proportions are flattened. Though the insect may have semi-opaque wings, most have clear wings with yellow-brown veins.

The male eyes are larger than the females and are divided into upper and lower segments. Aside from having smaller eyes, the female Bibio's head is also slightly smaller and flatter. After mating, the female deposits between 200 to 300 eggs in loose soil, then dies. The larvae scavenge on roots and decaying plant matter until they pupate. The adults emerge in early spring and swarm during mating, though they can be found throughout spring and summer.

For more information and photographs of other Bibio species, click here to check out this virtual field guide.

A Bibio natural. Igor Stancev Photo.

Bibio live in large fields, meadows, gardens, or other open spaces that contain water and moist soil. Fly fishermen should look for them in areas with fertile surroundings like lakes, spring creeks, and meadow streams not expect them in rocky canyon waters. Often times they will swarm along the shadows of low hedgerows and bushes on sunny days.

Adults typically fly haphazardly and are considered clumsy fliers, regularly bumbling into plants and people. Because they commonly fly between two to five feet off the ground, a great many end up in the water, especially if there is a breeze. Once on the water, they panic trying to break free from the water's grip, creating a commotion that catches the attention of big trout.

Most imitations are tied on #12-18 hooks and fished with fine tippets since trout are often "educated" in areas like the Henry's Fork where Bibio can be found. Stillwater fishermen often twitch their fly to mimic a Bibio struggling on the surface, but river anglers can get away with using traditional dry-fly tactics.

Because of their abundance, Bibio hatches have been a staple in British Isles fly fishing for some time, though they are only recently gaining popularity among American anglers. In the U.K. and Scotland, Bibio hatches are the first to cause worthwhile rises, beginning sometime around the middle of April and ending in the middle of May.

Igor and Nadica Stancev's Bibio imitation. Hans Weilenmann Photo.

Igor and Nadica Stancev, a husband and wife fly-tying team from Macedonia, have created an ultra-realistic imitation of the Bibio. Some characteristics that make this fly especially unique are the red collar that is clearly visible on some naturals, and the use of black foam to make the thorax bulky and help keep it riding on the water's surface.

Mike Lawson has been fishing Bibio patterns on the Henry's Fork since the early 1970s. He says that it is important for anglers to realize how significant Bibio hatches can be in the slow water sections of the Henry's Fork.

In the May 2003 issue of Fly Fisherman, he explains how anglers that don't know about the Bibio hatch have difficulty hooking fish. Because the Bibio coincides with other popular hatches like the PMD, Western March Browns, and Baetis, anglers are stumped when rising trout consistently refuse their offerings. His advice is to tie on a Bibio imitation even if you can see fish feeding on PMDs or caddisflies, it is highly likely they will take it. In a pinch, a slender beetle pattern will work. Check out Lawson's other tips on fishing Bibios and read how to fish one of his favorite terrestrials, the beetle, in the May 2003 Fly Fisherman.