The only thing that you are sure to find if you walk through the countryside with your eyes shut is dung. And every heap of dung has its residents; on it, in it and under it. On it we will find adult flies, in it, larval flies and quite often beneath it fly pupae. The flies that inhabit dung are many and varied and in these brief notes I hope to take the reader on a short visit to the enchanting world of the dung flies.
Dung flies are far more important than you would think. Without them we wouldn’t just step in it occasionally, we would be up to our necks in it, and probably beyond. For the dung files do not accumulate on the dung merely for sunbathing, the purpose is far more serious than that. They assemble in pursuit of romance, the aroma calling them in to a lover’s tryst. After brief preliminaries, mating takes place. Then the female will lay her eggs in the dung and the early stages (the larva or maggot) will feed, consuming the dung with apparent relish. And so the cowpat has been the dance floor, the bedroom, the maternity ward, the restaurant and the kindergarten.
You may well feel that dung is dung and, if you should step in it, well, of course, it is all much of a muchness, but if you were to eat it you would soon discern the subtle differences; from the smooth cowpat to the coarse horse dung, through to the rather strongly flavoured badger, dog and fox, right down to the rabbit, and for delicate palates there are bird droppings.
The big furry golden dung fly Scathgphaga stercoraria will be found chiefly on cow dung, but occasionally on deposits of other mammals. Amongst these flies on cow pats you will also find the much smaller black flies that are loathe to take flight, preferring to run into the surrounding grasses. These are called Sphaerocerids, a large family of some one hundred British species. Many Muscid type flies will also be found, including the very distinctive Mesembrina meridiana, a large shining black fly with orange bases to the wings. All three British biting muscids, including the stable fly, breed in dung. Some small acalypterate flies like the tiny yellow Chryomyid with green eyes, Chryomyia flava, live on bird droppings. Obviously these are the connoisseurs of the excreta eaters.
Now apart from those flies whose larvae actually consume the dung, there are, of course, those that consume the consumers. Many of the adult flies seen on the dung will actually have predatory larvae that will spend their larval stage seeking out the dung feeders for their own sustenance.
Mention should be made here of a dung frequenting pupa that finds itself amongst the dung almost by accident. This is the pupa of the internal parasite Gasterophilus which lives in the stomachs of horses as a larva and is excreted at the end of its larval development, and so finds itself deposited unceremoniously from a height of about three feet amongst a small heap of manure. On emergence the adult Gasterophilus leaves the dung never to return.
One could get the wrong idea about flies and dung. In fact only about 5% of our flies are associated with dung. So when you are eating lunch and a fly arrives for it’s share remember only one in twenty has dirty feet. Deciding which one is the problem.