Every summer about this time, I get calls and letters from readers terrified of "giant mosquitoes" they find under a porch light, or in the house trapped by window screens. But they are not mosquitoes. They are crane flies, and they commonly visit illuminated porches. The adults are easy to recognize -- they really do look like giant mosquitoes. But crane flies are harmless. Though some species of crane flies even have long, tubular mouthparts like a mosquito, they use them to drink nectar, not blood. And when they fly, they lack the mosquito's tell-tale whine. With more than 1,400 mosquito species in this country alone, the crane fly family (Tipulidae) is the largest family of flies in the world. Most have extremely long, slender legs that break off easily. Some look like winged daddy longlegs. Their wings are generally large, clear and crisscrossed with a network of veins.
The largest of the crane flies can attain a body length of more than 1 inch. Mosquitoes, on the other hand, are much smaller. About 150 different mosquito species occur in North America, and most are less than 3/8 inch long. Notorious for their blood-sucking and disease-transmitting habits, mosquitoes deserve their bad reputation. Interestingly, however, it is only the females that drink blood, which they require for egg production. Before they can siphon up animal blood, they must dilute it with their saliva, which they deliver through their syringe-like, tubular proboscis. It is this saliva that causes intense itching and transmits mosquito-borne diseases. Males drink plant nectar and juices.
Another difference between crane flies and mosquitoes is the impact each has on humans. Whereas the diseases transmitted by mosquitoes (malaria, yellow fever, encephalitis) cause serious illness and death, crane flies have little effect on us. The larvae of some crane fly species feed on living plant tissue and may account for minor crop damage. While crane flies have not been thoroughly studied, we do know that the adults of some crane fly species drink flower nectar, while many others do not eat at all as adults. But none of them ever feasts on humans.
Scott Shalaway is a biologist and author. "Wildlife," his other Post-Gazette column, runs Sundays in Sports. Shalaway can be reached at scottshalaway.googlepages.com and RD 5, Cameron, WV 26033.