Though big, they won’t bite

Adult crane flies are quite active this time of the year, often showing up on and in houses.

Though sometimes called “mosquito hawks,” these large, absurdly-leggy, delicate insects dine only on nectar as adults — if at all. The mouthparts of many crane fly species don’t actually function, in fact: those short-lived adults live only to fly about, mate, and lay eggs. So crane flies won’t bite you.

Crane flies can’t even sting you. The pointed structure you might notice at the end of the long, slender abdomen of some crane flies is not a stinger, but the female’s ovipositor, used to lay her eggs. The ovipositor also is the connection point when two crane flies are mating, joined together at the tail ends as they attempt to walk or fly in tandem.

Huge numbers of at least one species of crane flies might hurt your yard, however: European crane flies lay eggs in grassy areas — such as lawns — where the large “leatherjacket” larvae feed on plant material — such as grass roots. In fact, some entomologists have speculated that the ultra-long legs of crane flies may be an adaptation for laying eggs in soil beneath grass.

Week and rather haphazard flyers. Crane flies are the largest family in the insect Order Diptera: “Di” for two; “ptera” for wings — insects with two wings. (Beetles are not in this Order because, although when they fly they look like they have only two wings, the front wings of beetles are modified into wing covers.)

Other two-winged insects include houseflies, deer flies, horse flies, hover flies, midges and mosquitoes.

Although they’re all very long-legged, the more than 15,000 species of crane flies are fairly diverse, with bodies ranging in length from 2-60mm (1/8th of an inch to 2 ½ inches), with some tropical species growing in overall size to as much as 100mm (four inches) across. Crane flies are found world-wide and we have several species here — look for variety in size and in the patterns of dark splotches on the wings, as well as markings on the abdomen.

The Oregon Coast’s most noticeable native crane fly (Holorusia hespera) often has a handsome square dark spot on each wing. By some reports, this giant can grow to 3 inches across the wings; including the legs, a giant crane fly could cover the entire palm of your hand.

Follow a crane fly until it lands and you’ll have a clear view of the halteres attached to the thorax just behind each of the two wings. Although halteres are characteristic of all Diptera, those on crane flies are especially large and noticeable: slender with a knob at the end and about as long as the animal’s antennae, they look like minute matchsticks poked into the sides. Too, when most crane flies alight they tend to leave their wings spread out, rather than folded back, making it easier to see the halteres.

When the insect flies the halteres vibrate in a specific pattern, acting like a gyroscope to help with balance and navigation. (The word, “haltere,” is a Latin name derived from a Greek word for weights used in jumping.) Virtually all Diptera have halteres, though some are quite small and rudimentary. Perhaps the ultra-long legs of the crane flies require ultra-heavy halteres to maintain balance.

Don’t be put off by these fairy-like flyers. Let them do their thing outdoors and gently herd indoor visitors outside to safety.

For information on how to arrange an exploration of our fascinating natural history for your group or your visiting guests, contact Marty at 541-267-4027, or email mgiles@wavecrestdiscoveries.com. Questions and comments about local natural history are welcome.

(Back by popular demand, much of this content ran in The World on May 16, 2009.)