Thursday, July 23, 2009

Summer World IV: Crane Flies Dance

Crane fly (mosquito hawk) from June, 2007 in Barton, Vermont

Dancing crane flies in Wilmot, New Hampshire, June 2009

Do you remember the photograph above of two crane flies enjoying each other's company? There have been many crane flies in the house this summer. That is good; they eat many mosquitoes and with the rains all summer this year, we have many mosquitoes. But in Summer World, Bernd Heinrich gives the life of the crane fly poetry. It was the summer solstice in Maine, 2007. Heinrich explains that while June 21 is the beginning of summer for us, it is the middle of summer for many species of animals. And the day was so lovely that it was sufficient cause for dancing to celebrate the season. Heinrich's description of the crane fly dance describes exactly what happened in the beginning of summer with the crane flies in the bathroom:
Our outhouse is open at the front, and it faces deeply shaded sugar maple woods. The dancers — two or three dozen of them — each have six long, spindly legs. They jitterbug up and down and forward and back in a dark corner just under the roof, and they are worked up to a frenetic speed. Undoubtedly they are expert performers. They ought to be. They've probably been doing one or another version of their act for more than 225 million years, since the Triassic period. And indeed, their performance doesn't disappoint.

Most of the dancers are single, but several have partners to whom they are firmly attached — by their genitals. The members of a pair face in opposite directions, and when — more often than the singles — they come to rest, they dangle with one holding on to the ceiling with its front legs while the other dangles below.
Crane flies are relatives of mosquitoes. They are called crane flies because their legs are so long. Heinrich says that their bodies are 1/3 of an inch long yet their legs are three times longer (1 inch). And if you touch a leg, it could fall off. Dropping legs is a defense against predators. The sexes can be differentiated by the ends of their abdomens. A thicker, pointed abdomen is female and a thinner, blunted abdomen is a male.

The summer dance that Heinrich describes is mostly performed by the boys. Once a boy attracks a girl with his dance, they mate (my first photo) and then they stay together for hours. In his sample, Heinrich's male crane flies outnumbered females by 28:2.

I would so enjoy reading other local observations from other Summer World readers. I will have a couple more of my local observations in the days to come. Meanwhile, click on the book below and read it!

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  1. I loved the explanation about the "dance" of the crane flies, and the photo is great. (I stumbled on this while trying to figure out what the bouncing -- I've seen it for years -- is about.)

    However, my other readings about crane flies, which are also called "mosquito hawks," insist that they do not eat mosquitos! In fact, the adults of many species eat nothing at all. They just mate (and dance).

    Also, One source says there are, I think, 14,000 species. They have more species than any other kind of fly!


  2. No I didn't know that, Robert. Thank you. I also didn't know they are the largest group of flies in the world. Try reading Heinrich — somehow his books stay with me long after I read them and I see the world more clearly. Thank you again!


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