It’s late spring in Tuscon and we’re about to transition into summer. This means that a lot of insects have been making an appearance in the area recently. In particular, we’ve been invaded by one type of insect that I get questions about all the time. It’s one I can ID without even seeing it, based solely on the description of non-entomologists. The question is always this:
“What is that big insect with the really long legs that looks like a giant mosquito?”
The follow up question is always this:
“Does it bite?”
In case an image isn’t jumping instantly to mind the way it does for me, this is the insect that people are asking about with this question:
Crane fly, top view
Crane fly, side view
This insect is a crane fly (Order: Diptera, Family: Tipulidae). That means it is NOT a mosquito (Order: Diptera, Family: Culicidae)! Crane flies are large, slender flies with long wings and very long legs. In the Tucson area, they are often about 3/4 inches long and with legs over an inch long, but they can get even bigger in other locations in Arizona. These are big flies! They also have a V-shaped line on the thorax and large large compound eyes.
I’ll admit that they do look a lot like mosquitoes, but there are several key differences. The size is a big consideration. Crane flies are often really big flies while most mosquitoes are, at best, medium sized flies. Even if you’re looking at one of the smaller crane flies, one that is in the mosquito size range, there are several key differences to look for. The mouthparts are all wrong. Look at this photo of the crane fly, zoomed in to focus on it’s mouthparts:
Crane fly mouthparts
Notice how there’s no long, needle-like mouthpart? Mosquitoes use their proboscis to pierce the skin of their victims to suck their blood. Crane flies, on the other hand, eat nectar or don’t eat at all. As a result, they have thicker, blunt mouthparts with all kinds of crazy looking doodads sticking off them or no mouthparts at all. (In answer to question 2 above, no, they don’t bite!) And if that isn’t enough to convince you they’re not mosquitoes, take a good look at the wings. Crane flies have smooth, membranous wings with no scales while mosquitoes usually have scales along the wing veins.
Crane fly larvae have a special place in my heart because several species have aquatic larvae, though many species live in the soil. They’re really pretty disgusting looking, but that just makes me more fascinated with them. Take a look at the larva in the image below and see if you can figure out why they’ve earned the common name leatherback.
Crane fly larva
Crane fly larvae have distinct heads that are often nestled down into the thorax and are hard to see (case in point: the head is on the left side of this larva). The back ends are particularly interesting. They have a ring of fleshy projections, often looking like tentacles, that surround the pores they use to breathe, their spiracles. These tentacles make these really huge, fleshy larvae look extra awesome! Unfortunately, I have never figured out what the insects use those lobes for beyond their usefulness in species identification.
I wanted to finish by mentioning one other structure that is very visible on crane flies. Like all flies, crane flies have only 2 wings. But did you notice those little knobby things where the hind wings would be? If not, take a look at a zoomed-in image of them here:
Crane fly halteres. Notice also the v shape on the thorax!
Those structures are called halteres. Halteres are the remnants of the hind pair of wings and have been modified into new structures. They are thought to be very important during flight, acting like a gyroscope to tell the fly how it is oriented in the air. Crane fly halteres are very large and often highly visible due to the way the flies hold their wings out at rest – they’re an excellent fly to illustrate these structures. The next time you see a fly, take a close look and see if you can find the halteres! They may be very small, but almost all flies have them. Those tiny little wing nubs are likely why flies are such amazing fliers and responsible for their mid-air acrobatics, so they’re very important structures.
Next up is a series of posts on building a pond to attract aquatic insects, so check back in to learn all about my experiences building my pond. Perhaps you’ll even be inspired to build your own!
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