The Urban Pantheist

A small delicate fly, about the size and shape of a mosquito, drifts in from the porch door into the kitchen. I stifle the impulse to swat it--it's a reflex, an unconscious motion that many of us succumb to, to smash a flying insect. But mosquitoes are so rare in December in Boston that if I saw one it would be better to catch it and identify it for novelty's sake if nothing else.

You can see by the way this fly stands on the wall, all six legs down, that it is not a mosquito. Most mosquitoes land head down, back end up, with the last two legs off the surface--all the better to take a quick drink of you. To that point look at the fly's head: no proboscis.

This harmless visitor is a winter crane fly Trichocera sp. It is active in the warmer parts of the colder months, an adaptation that allows it to avoid predators. Their larvae are little white maggots that chew their way through compost and manure and wet vegetation, benefitting from habitat concentrated around humans such as leaf piles, rodent burrows, and even stored root vegetables.


One of my favorite things about crane flies is how their halteres are big enough and exposed enough to be visible to the naked eye.

Winter Crane Fly, Trichocera sp. (pretty sure, although that urban entomology handbook would be very helpful right about now)

Twice in different workplaces I have been present when this insect caused alarm. First was at Drumlin Farm, on the mosquito netting meant to protect captive birds from West Nile Virus. (I posted about it, but I'll be darned if I can find that post.) It was long past mosquito season, and it made me nervous: just how many months a year did I have to worry about these things? Well, I learned it was a crane fly, a harmless creature that looks mosquitoish. I had previously known crane flies to be quite large insects, much bigger than mosquitoes, but it turns out there are many species of many sizes, and this kind was just the right size to fool me.

Then last week, a coworker called me over to a dumpster on zoo grounds, mostly empty but for some debris and puddles. Here it was early January and it was swarming with flying insects--quite mosquitoish in appearance. I swung my hat through the swarm and snagged one to look at, expecting to see a non-biting midge. Instead I recognized the small crane fly from six or seven winters ago. Today I found one resting on the ice on the roof of a golf cart, and took the picture above.

If you're still having a hard time distinguishing this animal from a mosquito, look first at the posture. Most mosquitoes stand with their heads down and their rears up, with their back legs up like the dainty pinkies of a tea drinker. They also have scales along the veins of their wings--a difficult field marking to notice at a distance, perhaps, but distinctive once you learn to see it. And of course, their mouthparts are very different--mosquitoes bearing cruel and complex probosces to exsanguinate us (or somewhat reduced probosces to draw up nectar if they are males) while winter crane flies, well, you can see their mouthparts are a blunt little affair. I haven't found out what it is that they eat, and they may very well eat nothing at all--a situation not that unusual among insects. Their larvae live in and eat wet rotting organic material.

Some winter crane fly species survive as inactive larvae or pupae from spring to fall, and emerge as adults in winter to breed. This schedule allows them to avoid most of the aerial predators like dragonflies, swifts, and swallows. Their maggots are likewise protected from flesh flies, rove beetles, and other insect predators. Winter crane flies are sometimes called "winter gnats" especially in Britain.