Sunday, 17 May 2009

Show us your legs

The brain of a fly isn't much but there must be something going on in there. Yet even in these internet days its really difficult to find out much about the behaviour of St Mark's Fly. Bamburgh dunes were full of these black dangley-legged things today. Facts established: so called as they tend to emerge on St Marks day (April 25th); males have larger eyes than females (so that's a male in the top photo); males do an up and down flight to attract females.
Unaswered questions:-
  1. Is it just the males that dangle their legs in flight?
  2. If so, does the length of their dangling bits determine their mating success?
  3. If one emerged 2 days early would it be St George's Fly?


  1. Hi Nyctalus,don't really know the answer to any of your questions but have discovered two random facts. 1. St. Mark's flies belong to a group of flies whose antennae are carried underneath the eyes - the reverse of the situation in most insects.2. The males have different-sized facets (ommatidia) on their eyes, with larger ones in a distinct zone at the top of the eye (all-the-better-to-see-you-with) - I'll catch one and have a look at their eyes under the microscope. I really like the in-flight picture - images of animals in their habitat, rather than just portraits, are far more interesting. There are a couple of good web sites for dipterists, at

  2. Thanks for breaking my comments duck and for the 2 interesting nuggets.
    I agree with you about habitat shots but I have to say that flies are terrible things to photograph in flight - that one was sheer luck and I dumped the other 20 tries...
    Thanks also for the web site tips- and I'll watch out for your eye close-ups.

  3. Hi Nyctalus, there's a small contribution to the literature on St.mark's flies at

  4. Delighted to see that you remembered to follow up on the eye close-ups with a great post. I've left a comment on your blog. More questions I'm afraid!