Science of the Seasons: No need to crane for a look at this super fly

By Dr. David Wartinbee, for the Redoubt Reporter

Photo courtesy of Dr. David Wartinbee. Crane flies, like this female specimen, may look a little like giant mosquitoes, but they are no cause for alarm, as they are leaf eaters.

Photo courtesy of Dr. David Wartinbee. Crane flies, like this female specimen, may look a little like giant mosquitoes, but they are no cause for alarm, as they are leaf eaters.

Buzzing and bouncing on the side of the house, under your eaves and above the grass lurks a creature that must be the super ninja version and the biggest mosquito you have ever seen. It looks big enough to take a full unit of blood at one sitting. Be afraid!

In Alaska, we pride ourselves with having the biggest, strongest and meanest of critters, so this giant, blood-sucking machine seems to fit in with that mindset. But fear not. This bumbling fly is completely harmless. It may look like a mosquito with a stinger on its tail but it can’t feed as an adult, and that “pointy thing” on its abdomen is for laying eggs. Sorry to burst your bubble, guys, but you won’t be able to prove your machismo by handling this large fly.

So what is it? It’s an adult crane fly, a member of the Dipteran family Tipulidae. They have very long, spindly legs and an elongated abdomen that may be 3/4 of an inch in length. Their wings are usually pigmented and may have intricate designs on them. Like all Dipterans, they have only one set of wings and a set of interesting balancers called “halteres.” These halteres look like a tiny ball on the end of a stick but are actually a modified, second set of wings. They vibrate as the insect flies and help maintain smooth, coordinated flight.

The adult crane fly is a weak flier but it slowly moves around, looking for a mate. Once mating is completed, the females will look for an appropriate place to lay eggs. She then uses her pointed, abdominal ovipositor to plant the eggs into moist or marshy soil. Alternatively, she will lay eggs into moist leaves packed along a stream.

The adult will only survive for a couple weeks, but they can be an important food source for bats, birds, spiders, shrews and other insect-eating animals. The majority of its life was spent as a larva, and that can be just about a year.

However, in some arctic situations, the larvae may take a couple years to reach maturity. They are fairly common in streams and springs where organic materials accumulate. Crane fly larvae are well-known for feeding on leaves that enter streams and rivers in the fall. While they are chopping up the submerged leaves, most of the protein they acquire is actually from bacteria and fungi that are living on the moist leaf.

There are some species of crane fly that grow in moist vegetation, such as found in a thick lawn. Here they feed on dead grass, leaves and perhaps some living plant material, too.

Crane fly larvae are wormlike and can be almost as thick as a pencil. Some species will be more than an inch long. Many a budding stream ecologist has been startled when one of these chubby larvae suddenly appears, wriggling back and forth when separated from a protective pack of leaves.

The anal end has the ability to inflate itself with hemolymph, much like a tiny balloon. Imagine a larva with a globe-shaped swelling at its back end. By periodically swelling this area, the larva can lock itself in position as it pushes and eats its way through a pack of leaves.

The anal end of the larvae also contains spiracle openings that can enable some species to acquire oxygen. Many larvae will keep this end exposed to the air while the rest of the body is submerged. However, many of the larvae are completely aquatic and can absorb oxygen directly through their tough, outer skin.

As larvae complete their growth, they move out of the leaf packs and head closer to shore. However, they tend to stay under leaf and litter where the humidity is fairly high and they are unseen by potential predators. Here they form the pupa stage.

During the pupa stage, there is a huge transformation or complete metamorphosis. The fattened larva becomes more slender with easily defined head, thorax and abdominal sections. The wings, halteres, legs and reproductive structures are also formed in a week or so. When metamorphosis is completed, the adult emerges and becomes an aerial adult in a terrestrial world. Then it can start frightening the uninformed as it looks for a mate and avoids predators.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.

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2 Comments

Filed under ecology, insects, science, science of the seasons

2 responses to “Science of the Seasons: No need to crane for a look at this super fly

  1. I always enjoy Dr. W’s articles!

  2. Nikki

    1st of wow these are amazing creatures stunning and they wont bite humans they are very delicate and gentleif u find them in ure home they’ll usually flie agaisnt walls trying to find a way out or rest on the wall but if u come near them they get scared easy the best way to catch them is corner them in cover them with ure hands and close ure hand shut it’ll trap them and then u just open the door and set them free:) u just have to be gentle with them they are very fragile creatures their legs break easy

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