Sunday, 7th July 2002, West Yorkshire
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There's a stir as I walk past the pond. A wisp of small flies swishes
up for a moment then settles again on the carpet of duckweed. I crouch
down to take a closer look; there are 30 or 40 of them, bronzy in colour,
up to 8mm long.
The flies are using the pond as a lek; a display ground where the males
vie with each other to attract the females. The males, which are larger
than the females, have brown patches, edged with a crescent of a lighter
shade, at the end of each wing.
aim is to entice a female to land close by or, failing that, to land in
front of a female and attract her attention by performing a wing-waving
display; wings out, wings forward, wings back - a motion like rowing a
boat or waving semaphore signals. Sometimes they'll repeat this a few
times at about the interval that it would take you to say, in a leisurely
way, 'one, two - one, two.'
The female often plays hard to get. She'll turn away on the spot. The
male (left) flies up and settles to face her again, an inch or
so from her, and performs his routine again. The female might turn again
- in which case he'll fly around again to face her - or she might get
bored of the whole thing and fly off. Occasionally the dance will result
in a mating. Sometimes a male will display to another male who will wave
his wings as if to show he's not a female and the dance will end there.
There's a lot of activity and the whole thing looks like a disco in full
swing, except the females aren't dancing in a circle around a pile of
I'm calling them picture-wing flies, but I'm just going by the wing-waving
behaviour. True picture-wings seem to be smaller than these, and with
motlier wing patterns.
I've also seen the same flies, in smaller numbers, gathered around an
almost dried-up puddle.
A local naturalist, John Coldwell, e-mailed me with
You may (or may not!) like to know that your 'picture winged' flies
were almost certainly the dolichopodid Poecilobothrus nobilitatus.
Here's another small fly but this one is tiny, only 3.5 mm long, 5 mm if
you include the wings. It's the time of year when one or two dead insects
start appearing on the desk below the studio window. With the aid of my
30x pocket microscope I
sketch the details of the red multi-lensed eyes, the whiskers on its head
and thorax (which I guess help it judge its movement through the air), the
hairy legs, the veined wings and the stumpy thorax. The little microscope
is handy to carry about but it's got such a small depth of field that I
have to change the focus five or six times to sketch the whole fly. I know
I don't have a chance of identifying it.
The little mushroom shaped organ that I've drawn in more detail is one of
a pair of halteres. You can see in the sketch that it sits just behind the
wing. In two-winged flies, also known as true flies or Diptera, what would
be the rear pair of wings in a dragonfly, bee or butterfly are modified
into these organs which are probably an aid to balance in flight.
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