Winter Crane Fly (Family Trichoceridae)

Salutations, BugFans,

Mild weather has kept insects flying/crawling late into fall this year (some of those anonymous, tan “winter moths” have been decorating the front porch). This Winter Crane fly was photographed one balmy evening in the fourth week of November.

Winter Crane Flies

Winter Crane Flies (family Trichoceridae), like Phantom Crane Flies (family Ptychopteridae) are not-too-distantly related to the common (and often much larger) crane flies in the family Tipulidae. Trichoceridae is a small family with just under 200 species worldwide, and of the 27 or 28 species in North America, all except two or three are in the genus Trichocera (as one source points out, because species IDs depend on hand lenses and tiny legs and wings, bugguide.net does not differentiate among species photos within the genus Trichocera).

They are variously called winter gnats, winter midges, and winter crane flies (quick reminder—according to convention, in the names of the true flies (order Diptera) (“two wings”) the word “fly” is a separate word. Deer fly. House fly. In non-Dipteran families, it’s usually part of a compound word—dragonfly, mayfly, dobsonfly, scorpionfly, firefly, etc.). Though they’re very similar to Tipulids, winter crane flies have ocelli (simple eyes) on the top of the head that monitor light/dark, and the pattern of veins in their wings is different. WCFs are about half-again as large as mosquitoes.

  • Winter Crane Flies

Besides the BugLady’s front porch, WCFs perch inside the mouths of caves, mines, hollow trees, and decaying logs in cool/temperate climates. Many species of WCFs overwinter as adults in sheltered nooks and crannies and are abroad in the chilly (but not freezing) air of early spring and late fall—even during mid-winter thaws, when they may be seen walking on snow. Other Trichocerids prefer “normal” insect temperatures. Males form mating swarms, bobbing up and down a few feet off the ground. In 1984, scientists Pratt and Pratt reported that “swarms of males are seen dancing in the late afternoon sunlight, sometimes thousands of individuals in hundreds of swarms over many acres of lawns and open woodlands.” Females fly less, but they will join the dance to find a mate before returning to the ground to lay eggs.

While the larvae of many Tipulid crane flies are aquatic, winter crane fly larvae (maggots) are generally found in damp-ish situations with organic decay—under leaf litter, in fungi, caves, manure, rodent burrows, and sometimes in stored root vegetables. There, they scavenge on rotting plant matter and sometimes on animal material like dung and carrion (the BugLady found a couple of “teasers” about Trichocerid larvae being used in forensic investigations but could discover no details). The larvae pupate in the ground and, according to somethingscrawlinginmyhair.com, the pupa moves to the surface “before the adult emerges” (yes, some “rigid” some pupal cases are mobile).

Adults are said by most sources to eat nothing (there’s precious little fly food available during their flight periods), but they’ve been collected at molasses traps, which suggests otherwise. They provide a nice (little) morsel of protein for birds in winter, and the BugLady found a nifty paper about the importance of WCFs and Tipulid crane flies in the winter diet of horseshoe bats in Great Britain.

An odd lifestyle—trading the joys of eating for the joys of a relatively short, potentially predator-free life in the cold, but it’s worked for WCFs for about 180 million years.

And a Scanning Electronic Microscope (SEM) image at: Science Source.

 
The BugLady