Crane Flies Are Another Sign of Spring
Ro Wauer, March 2, 2003, The Victoria Advocate, © 2003
Several of these long-legged "mosquitoes" are out and about during these warm spring days. But crane flies are very different insects than the troublesome mosquitoes. Although both are members of the Diptera Order of insects, crane flies are members of a totally different and unique family - Tipulidae - that includes several hundred species in North America. Mosquitoes are Sumuliidaes, a family that also includes gnats and midges.
Crane flies are much larger than mosquitoes, and they fly about in a slow and rather clumsy manner, sometimes even bumbling into lights, doors, and even mouths of predators. These daddy-long-legs of the air have also been called "drolls of the insect world," due to their unassuming personality. Yet we often find great swarms in cool, damp places, such as in culverts or under concrete bridges. And after dark they are often attracted to lights. Oftentimes they come to the outside windows of lighted rooms.
The swarms of crane flies often behave in a very strange way, by bobbing up-and-down by raising and lowering their bodies by bending their long legs. This behavior is not well understood, but some entomologists suggest that it may be a way for the males, that dominate the swarms, attract passing females. Others suggest hat it may more related to safety-in-numbers. Certainly, finding a swarm of these long-legged bugs that suddenly began to bob up-and-down, can not help but give one pause.
There are about 90,000 species of Diptera or true flies worldwide, including almost 17,000 in North America. Butterflies, dragonflies, mayflies, and stoneflies are not true flies. All of the true flies possess a single pair of wings and a pair of short knobbed projections called "halteres," located on their bodies just behind the wings that serve as balancing organs. Although they are difficult to see on small flies, they are fairly easy to see on crane flies. Halteres act as a second pair of wings, like gyroscopes, vibrating rapidly in opposition to the insect's wingbeats. When the wings move up, the halteres move down. If one of the halteres is injured, the insect can no loner fly, but sideslips and yaws out of control. In people, this sense of balance derives from the structures in the inner ear. If something goes wrong with this mechanism, a person has difficulty in navigating and even standing up.
Crane flies, unlike their mosquito cousins, have no sting or bite; they are totally oblivious to humans. One usually can get within a few inches for a close-up examination. Except when disturbed, they will stay in place, so you can examine their various features. They possess a narrow abdomen, narrow wings, and absurdly long legs. Occasionally they can be found walking about on tree trunks or logs or damp leaf-cluttered ground. Many of those found on the ground or on logs are males in search of a female. They may even sit beside a pupae until the female emerges and mate scarcely before she has freed herself of the pupal skin. The female crane fly, once filled with eggs, deposits them on the surface of rotting wood or pushes them into soft pulp. The larvae, tiny greenish grubs, crawl about below the surface of the ground, feeding on roots and seedling plants, sometimes killing them. Although adult crane flies are most obvious and attract the greatest attention, the larvae, that are rarely evident, are biologically more important.
But in spite of their relative unimportance, adult crane flies are more fascinating. Finding a swarm of these long-legged insects on some damp structure, or several individuals flying about one's property on a warm spring day, seems to be a telling signal that the new season has truly arrived.