Those wretched flies!

Heleomyzid fly species

– from Richard Knight at The Cwm

Two years ago I was asked by a well known local naturalist “when did you last see a house fly ?”.  I thought for awhile and came to the realisation that I hadn’t seen one for several years.  Then came the summer of 2010 ! ……..

Throughout July we, and from my enquiries lots of other folk, were plagued (and plagued) by flies in the house.  While local sales of sticky fly papers and fly-sprays soared I was contacting local entomologist Mike Paskin. My description via telephone led him to believe they may be Lesser House-flies.  I sent him a sample of the ones flying around our kitchen with some of those found dead on the window sill  –  are they the missing house-flies I asked and if not who are they.

Soon I had a reply  :-

Dear Richard,

Some notes on the flies from The Cwm :-

There were no Lesser House Flies (Fannia) in your sample, I discarded 3 badly damaged flies but none were Fannia.  However there were 2 male ordinary house flies – Musca domestica.  

There was one other Muscid probably Mydaea affinis.  I am not familiar with this group so the identification must be tentative, if correct it is a widespread but uncommon species, it has been bred from Boletus fungae –  the larvae would have been preying on other insect larvae feeding on the Boletus.

There was one female Rhagio scolopaceus (Rhagionidae) – larvae found in dry soil.

The remaining flies were all Dolichopus :-

Dolichopus discifer 1 male and 2 females, Dolichopus pennatus 1 female, Dolichopus popularis 1 male and 1 female.

Dolichopus are somewhat elongate flies c.5mm long, dark metallic green with long yellow or black (or mixed) legs.  The male has a pair of large claspers bent forward below the tip of the abdomen.  In several species the male has either the front or middle legs feathered or silvered towards the tip and these are waved at the female whilst courting.  Dolichopus often enter houses in large numbers, particularly in dry weather their larvae live in damp soil at the edge of ponds, streams etc. and they are presumably looking for a shaded damp place.

Some notes on other ‘Houseflies’  :-

Meatflies – Sarcophaga species are large grey flies with tessellated abdomens, true meatflies are now quite rare, if you see a similar fly now either in or outdoors it is more likely to be one of the closely related species whose larvae are parasites of earthworms. There are several other flies with grey tessellated abdomens, of very varied larval habitats, but most are a little smaller.

Lesser Fruit Flies – Drosophila species may be attracted to over ripe fruit they are very small yellowish brown flies often with the abdomen banded darker brown.

In the autumn several species of fly may enter houses to hibernate; the most conspicuous are Pollenia species  –  cluster flies, like rather large house flies but with wavy golden hairs on the thorax, these may have worn off the top of the thorax but are usually present on the sides. Their larvae are also parasites of earthworms.

A variety of flies are attracted to light, the largest are Tipula species  –  craneflies (daddy long-legs).  Many other insects apart from flies and moths are attracted to light, the ones most likely to be confused with flies are the large yellowish brown ichneumons  – they look rather like craneflies but have two pairs of wings  –  craneflies and all true flies have the hind pair of wings reduced to knobs.

Many other flies enter houses ‘accidentally’ but many of these like the Dolichopids are probably searching for suitably habitat or just sheltering from the sun; in very hot weather you often find very large numbers of flies just inside a woodland, presumably they have moved from the adjoining field to escape the sun and I imagine an open door is just as inviting.

True accidentals are most likely if there is a strong air flow through the house.

Last but not least, as you are probably only too aware, if you have your bedroom window open at night you will attract biting midges and mosquitoes. (Mike Paskin)

  Following further discussion with Mike it seems that yes the hundreds of flies flying round and around our kitchen seemingly quite at home were the ‘missing’ house flies Musca domestica but the ones at the windows trying to get out and perishing on the window sills were a miscellaneous selection looking for shade but finding themselves trapped.

 In Colyer and Hammond’s ‘Flies of the British Isles’ 1951 reprinted 1968 (The Wayside and Woodland Series published by Warne now out of print) there is a very readable account of houseflies (page 296) that begins   “If more than casual attention be given to the flies which occur in dwellings, it will be noticed that some of them appear to be perfectly at home and quite content to stay indoors, while others display a desire to depart which frequently leads them to a window, upon which they wander, in varying degree of agitation, seeking egress.  Examination of the latter kind, over a period, will reveal that they are accidental visitors; whereas the domesticated kind will be seen mainly to comprise two principal groups, whose occurrence indoors, by virtue of its frequency and regularity, is obviously not fortuitous …………  One of the two groups consists of both larger and smaller flies, which, if allowed, will wander over food, especially sweet substances, investigating it with the proboscis, or will rest upon walls, lamp-pendants and other places in the room where they leave traces of their stay in the form of ‘fly-spots’.  The other group comprises smaller flies, which fly in a characteristic manner for long continuous periods beneath lamp-pendants, in shafts of sunlight from windows and similar places.”

 Thank you Mike, and Colyer and Hammond.

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One Response to Those wretched flies!

  1. Janice says:

    Thankyou for that information – fascinating.

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