Smoke and insects

[Patrick Roper]

Reading the thread about smoke and butterflies reminds me of the
mystery of smoke flies (Diptera of the genus Microsania in the family
Platypezidae).  These little creatures often appear here in
considerable numbers in the smoke of summer bonfires in the garden.
The males swarm in the thickest of the smoke where it is quite hot and
difficult to breathe and the females seem to lurk in vegetation
nearby.  If the smoke column shifts in the wind, the flies shift with
it.

The curious thing is these insects have hardly ever been recorded away
from smoke, but they must be about "out there" in some quantity as
they appear very quickly when a fire is lit.  What do they do the rest
of the time?  Adding fuel, as one might say, to the fire of this
mystery is the fact that, as far as I know, no one has discovered
where they breed.  Often they have many mites on them implying that
they prefer dung, compost, rotting wood or similar, but despite many
experiments I don't think anyone has ever caught any in an emergence
trap.

Why do they like smoke?  Well it decidedly keeps the birds off them.
Did they develop in a smokey place, e.g. near volcanoes?  It may be, I
suppose, that the tolerance is widespread in insects (including
butterflies) but that smoke flies have "learnt" to make use of the
attribute to their own advantage.

Views on the origins of smoke flies (which I assume are found outside
Europe) and anything else about them would be welcome.

Patrick Roper