That mosquito with a wobble – it’s a crane fly

Crane flies have long legs and long, slender abdomens, but they are unpredictable fliers, with a tendency to wobble in the air. Enlarge photo

Courtesy of Sally Shuffield

Crane flies have long legs and long, slender abdomens, but they are unpredictable fliers, with a tendency to wobble in the air.

Mosquitoes are a natural part of summer. Luckily, in Colorado, we have fewer mosquitoes than many areas of the country. One of the luxuries of living in Durango is the ability to sit outside in the evenings without the fear of getting eaten alive.

Kids in our first session of summer camp at the Nature Center spend the last part of their day wading lazily in the Florida River. At first glance, it may seem they are encountering mosquitoes on the water, but on closer inspection, it is often the slightly larger crane fly.

Crane flies look like giant mosquitoes, but other than being flies, like mosquitoes, they are very different. Crane flies can be about an inch long and are very uncoordinated with a crazy flight pattern. Unlike most flies, crane flies are weak and poor fliers with a tendency to “wobble” in unpredictable patterns during flight, and they can be caught without much effort. Unlike mosquitoes, they don’t buzz or bite. In fact, adults don’t even have mouths.

True flies, such as crane flies and mosquitoes, are insects of the order Diptera. Their most obvious distinction from other insects is that a fly possesses a pair of flight wings as well as small knobbed structures called “halteres,” which are derived from their hind wings. Crane flies have very long legs and long, slender abdomens. The wings are often held out when at rest, making the large halteres easily visible.

Some colloquial names for crane flies include “mosquito hawks,” or “mosquito eaters.” However, these names do not describe them correctly. Because the adults don’t have mouths, they can’t eat mosquitoes, much less anything else. The adults only exist to mate, lay eggs and die. However, some predatory crane-fly larvae may eat mosquito larvae, hence the history of the name.

There are many different species of crane flies, and they are almost impossible to tell apart. Crane-fly larvae are wormlike and grayish, brownish or cream-colored. They can be anywhere from a half inch to 3 inches in length. Almost all crane-fly larvae live in water. The larvae have several spiracles on the end, which look like tentacles. The larva will stick this end out of the water to breathe air.

When larvae are fully grown, they will crawl from the water and burrow into mud or soil. Next, they will become pupae (resting stage), when they will slowly change into adult crane flies. Usually, they will spend the winter in the mud before they hatch the next spring and summer. Large amounts of crane flies hatch at the same time, and swarms of males “dance” above treetops looking for females. When crane flies are hatching, fishing is wonderful. In fact, the crane fly is a common fly used by many fly-fishers.

Crane flies can be a nuisance when they enter homes. But, because they don’t bite, they do no harm. They only come inside because they are attracted to light. They are important because they help break down dead plant material, especially dead leaves and stems on the bottoms of streams. This keeps the water healthy for fish and other wildlife. So, before instinctively reaching out to swat that overly large mosquito that has alighted on your leg this summer, take a second glance to make sure it isn’t a gentle relative, the crane fly.

sally@durangonature-studies.org or 382-9244. Sally Shuffield is executive director of Durango Nature Studies.