BUG OF THE MONTH: June 1994
Phantom Midges and Phantom Crane Flies
Copyright © 1994 by Louise Kulzer
This article originally appeared in Scarabogram, June 1994, New Series No. 170, pp. 2-3.
At one time, I clearly distinguished Phantom Midges and Phantom Crane Flies. More recently, however, I've noticed a distressing tendency to confuse the two. In trying to clear up my confusion, however, I discovered that the phantom flies are taxonomic phantoms as well as phantoms in name, having been classified in different taxonomic groups by different authors.
First, both phantom midges and phantom crane flies are true flies, order Diptera, and gnatlike flies, suborder Nematocera. Here's where the similarity ends, however. Phantom midges are mostly in the genus Chaoborus, and they exhibit their "phantomness" in the aquatic larval stage. Phantom midge larvae (see right) are almost transparent, have no legs, but hang suspended in the water column, buoyed up by large air vacuoles within the body cavity. They are predators themselves as well as one of the famed dietary choices of fishes. But wait-----predators with no legs to handle prey? Yes sirree. These fascinating phantoms have prehensile antennae with which they nab their prey. Being just above the mouth, this arrangment seems to work out just fine. They are fairly common in Seattle area lakes and wetlands.
The adult Phantom Midge resembles a mosquito, but is non-biting (Bland 1978). Usinger (1971) classifies phantom midges as a subfamily of the Culicidae (mosquitoes), the Chaoborinae. However, more recent texts assign them to their own family, the Chaoboridae. (I find this latter arrangement doesn't have the same bite as the former).
Now for Phantom Crane flies, genus Bittacomorpha. As adults, phantom crane flies are fairly large, long-legged flies resembling crane flies. The larvae, which are scavengers, live in mud or shallow water filled with decaying grass, rushes, or leaves, and breathing through long tubes (see left). It is the adult that earns the name "phantom" because of its flight behavior. It hangs or floats in the air rather than flies, spreading its long legs to catch the breeze, a little like ballooning in spiders. Phantom crane flies have black and white banded legs with swollen metatarsi filled with tracheae, presumably to enhance buoyancy. When the legs are vibrated, this insect indeed lives up to its name, giving the beholders a sensation of "spots before the eyes." I've only seen the Phantom Crane Fly once in Seattle, in Discovery Park near the north parking lot.
Usinger refers to phantom crane flies as phantom midges, no doubt contributing to my confusion, and puts them in the fly family Liriopeidae, false crane flies. Alexander (1920) classified phantom crane flies as the subfamily Bittacomorphinae of the family Ptychopteridae, as did Williams and Feltmate more recently (1992). Another source of confusion is to get Bittacomorpha, the phantom crane fly, mixed up with Bittacus, a crane-fly-like member of the scorpionfly order, Mecoptera. Bittacus adults, called hangingflies or hanging scorpionflies, typically hang from vegetation by the front legs, capturing prey with their hind feet (Bland 1978). Well, so much for my earlier statement about similarities. Let me try again. Phantom midges and phantom crane flies have very little in common aside from evoking a surreal sense of wonder in human observers. How's that?
Alexander, C.P. 1920. The Crane-flies of New York. Part II. Biology and phylogeny. Cornell Univ. Agricultural Experiment Station Memoir 38: 699-1133.
Bland, R.G. 1978. How to know the insects. Pictured Key Nature Series. Wm. C. Brown Co., Dubuque, Iowa.
Usinger, R.L. 1971. Aquatic insects of California. University of California Press.
Williams, D.D. and B.W. Feltmate. 1992. Aquatic insects. CAB International, Wallingford, U.K.