Sunday, September 18, 2016

Time flies like an arrow, crane flies like a wall

It's September, and no matter what your age, it's a time of change.  The nights have gotten chillier, morning breaths condense, and giant mosquitoes are now flying in open windows at night.  But no, they're actually not mosquitoes, but a species of non-biting species of fly called the crane fly.

Started noticing them hanging out on the wall by the school.  A mysterious ratio of 20 males to one female.

The way they perch on the wall is a bit unique.  Their heads are flush against the wall, the rest of the body hanging by the front four legs, and the rear legs keeping their abdomen pointed up.

The crane fly has only one pair of flying wings.  Most other flying insects would have two pairs.  If you look closely, you'll see a pair of club-like appendages that evolutionarily were the second pair of wings.  These halteres act as counterbalances for the crane fly, a feature that most other types of flies have.

What we see as the crane fly is actually a short-lived part of its life cycle.  The adult form lives for only a few weeks, doesn't eat, and it's sole purpose at that stage is to mate.  They mature around the same time of year to maximize their opportunity to mate.  Spiders take advantage of the bonanza of crane flies, whose gangly legs snag easily on webs.

Eggs are laid in damp soil, and the grubs feed on grass roots.  In large enough populations, they can devastate lawns.  Those of you who garden may have come across them as fat, grey caterpillar-like grubs.

Female insects that lay their eggs beneath the ground will have an ovipositor, or a tapered end of the abdomen.  Grasshoppers are another insect with this feature.

Males are typically smaller, and have a blunt end of their abdomen.

They seem to manage to be able to fly while copulated, though I have yet to get a good look at who steers.  I can't imagine it to be a romantic experience.


Susannah Anderson said...

Good post! My cat is having a field day with these flies; I haven't been able to catch one that doesn't have parts missing. They all seem to escape Chia's clutches eventually, so I think there will probably be a good crop of grubs chewing up my lawn, in spite of her efforts.

Tim said...

When I was more obsessed with spiders, crane flies were my go-to insect for luring them out of their retreats. The flies tended to hide in our long uncut lawn, and all I'd need to do is sweep the grass with my foot to get them to reveal themselves. They'd be slow enough to catch, even out of the air with a single hand. I felt even less guilty about using them as bait after I discovered their destructive nature with lawns.

Steve Daniels said...

Nice post Tim and great descriptive pictures of halteres and ovipostor (thanks for putting me on to this Susannah). Like the tip about spider bait too.

Tim said...

Thanks for visiting, Steve. Crane flies are probably one of the easiest insects to observe in our part of Canada at this time of year. They don't make too much of an effort to stay inconspicuous.

Bella Sinclair said...

I remember freaking out when I thought crane flies were giant mosquitoes. :) I don't think I've even seen one THIS close up. They are fascinating. Hope the start of your year is going wonderfully!