Wednesday, 22 May 2013

St Mark's Flies

Many people will have seen the St Mark's Fly, Bibio marci. It is a moderately large, black, clumsy-looking insect, flying sluggishly over meadows around St Mark's Day, 25th April. Its legs, with strong spiny hairs, dangle beneath the body, giving it a rather odd appearance. Even the eyes are densely hairy, giving my photograph a rather fuzzy appearance.

St Mark's Fly, Bibio marci. Byfield Pocket Park
22 May, 2013

It has been on the wing in this area for about a week so, in common with many other organisms, it is later putting in an appearance than usual. Much smaller is Bibio johannis. Logically it ought to be called St John's Fly - but it never is. This is a more common insect but its small size means that it is generally overlooked. Closely related to Bibio is the genus Dilophus. One very common member of the group is Dilophus febrilis, known as the Fever Fly from a mistaken belief in Sweden that these insects would swarm around the homes of fever victims. All the insects mentioned so far are known from Byfield Pocket Park.

Nursery Web Spider, Pisaura mirabilis (female)
Byfield Pocket Park, 22 May, 2013
Having photographed the St Mark's Fly I was about to put my camera away when I saw a female Nursery Web Spider, Pisaura mirabilis, on an adjacent leaf. This is quite a large species with the females reaching 15mm or so in length. The female carries her cocoon of eggs around until they are about to hatch and then builds a tent-like web, placing the cocoon within the tent and then guarding it until the spiderlings hatch.

     The male is significantly smaller than the female so mating is therefore a risky business. He improves his chances by catching a fly, wrapping it up and then presenting it to the female. While she is enjoying her meal he craftily nips round the back to mate. The late Bill Bristowe told of a case when the male, having had his wicked way, stole the fly from the doubtless astonished female and made off with it. Thankfully human males never behave like that...

No comments:

Post a Comment