Monday, November 7, 2011

Insect Swarm

During the summer, a sunset view above the Indian Grass fields will reveal myriad insect species illuminated by the slanted rays of the sun. After a few nights of below freezing temperatures, the insects drop off to practically none. Except for a few birds diving into the tall grass to roost for the night, all is calm and quiet.

All’s calm that is, until you notice swarms of tiny flies rising out of the grass. Some rise up as part of a swirling cloud, while others come up singly. The singletons drop quickly back into the grass, but the clouds may remain in view for up to half a minute before falling down out of sight.

The insects are only visible while backlit by the sun. This makes it hard to see anything more than a bright glow. Details of the insects are pretty much lost to the casual observer.

The swarm becomes nearly invisible when it moves down into the grass stalks. I tried many times to get close to an aerial swarm, but each time I tried, they would drop into the grass at my approach. I see these swarms every year, but I’ve never gotten a good picture. I was determined to continue stalking the swarms until I got a picture of one of the insects.

My pursuit drove a swarm into a nice orb web and one of the flies became entangled. This isn’t exactly how I had planned the encounter, but it did result in a member of the swarm holding still for a few seconds.

It appears to be a small species of Crane Fly. The swarms appear on warmer evenings right through to early spring. It’s not unusual to see large swarms during warm spells in the middle of winter. If they’re going to present such obvious and abundant display each year, I’d better get busy and learn a little bit about them.


  1. There are a variety of two-winged flies (Diptera) that fly in little swarms (mating aggregations) on the warmer days of the cool season. The most common are the "winter crane flies", as in your picture. There are a few more pictures at

    At warmer times of year, the diversity of insects gathering in such mating aggregations is much greater, and includes different species of flying ants that fly seasonally from April through early October.(Had to work that in!).

    Also, many flying insects are just trying to get from here to there, rather than gathering in tight, swirling swarms. Where would all the bats, and birds that feed on the wing, and dragonflies, and web-building spiders, etc., be without all this flying fodder?

  2. Hi James. Thanks for the information on the winter crane flies. I'll do a little research into their life histories and try to figure out what they're doing when they're out of sight in the grass.