This post is possibly not one for the squeamish, but lately I’ve become more aware of these bright little flies and given thought to the vital role they and their kind play in maintaining balance in our environment, so decided it was time to learn more about them. Yellow dung-flies are one of the most familiar and abundant flies here in the United Kingdom and indeed throughout much of the Northern Hemisphere. They are out and about from March to November and at their peak in the summer. Anyone that walks in the countryside, particularly in areas where there are large mammals will undoubtedly have seen them. They may look a little fearsome close up, but are harmless to us, they do not sting or bite people or other animals!
Common Yellow dung-fly or Golden dung-fly – Scathophaga stercoraria
As its common name suggests, the life of a Yellow dung-fly, particularly that of the males is centred on, yes you’ve guessed it … dung! They spend most of their lives either upon it, or looking for it. They favour cow pats, but are adaptable and will settle for the dung of other large mammals such as horses, deer or wild boar if that’s what’s available. Unsurprisingly here in Wales they mostly have to settle for that of sheep.
Dung-flies belong to the Scathophagidae family of flies which are integral within the animal kingdom in the role of assisting in the process of the natural decomposition of dung in fields and grasslands.
Description: 5-11mm long. Average lifespan is 1-2 months. Sexually dimorphic, males are golden-yellow with orange-yellow fur on their front legs and are larger than the females. Females are generally duller in appearance, more of a green-brown colour and have no brightly coloured fur on their front legs.
Males and females are attracted to fresh dung by its scent and actually approach deposits flying into the wind. Males spend most of their time on the dung waiting for females to mate with and being predatory insects, sometimes feeding on other insects that visit the dung, such as blow flies. Females on the other hand spend most of their time foraging in vegetation and only visit dung to mate and subsequently deposit her eggs.
The male-female ratio of flies on a dung pat is typically heavily biased towards males. Often several males can be seen waiting for a female to arrive, so if and when one does, competition to mate is high: the smaller, outnumbered females don’t have much say in choosing their mate.
The act of copulation lasts 20 to 50 minutes during which the couple may be subject to aerial attacks from rival males attempting to dislodge the male. When the act is completed, the male attempts to guard the female from the attentions of other males, although both males and females often mate with several individuals.
The adult dung-fly is mainly carnivorous, catching and eating smaller insects, but they also eat nectar. After mating females lay their eggs on the dung, where she selects small ‘hills’ on its surface, deliberately avoiding depressions and sharper pointed areas. This strategy is aimed at preventing desiccation and drowning thus giving eggs and offspring the greatest chance of survival. Depending on ambient temperature eggs hatch into larvae after 1-2 days. Larvae burrow quickly into the dung for their protection and proceed to feed on it; they also predate on other insect larvae also living in the dung. They grow rapidly and after 10-20 days the larvae burrow into the soil around and beneath the dung where they pupate.
The Yellow dung-fly has a short life cycle, a factors that has made them of interest to scientists, who have been able to study not only the insects themselves but also the effects various environmental factors has on them. For example:
The viability of a clutch of eggs depends strongly on the environment. In warmer climates a sharp drop in population occurs during the summer when temperatures increase to 28° or above. This does not happen in places with a colder climate such as Iceland, Finland and the north of Britain, nor at higher elevations.
The health of juvenile dung flies is in turn affected by the quality of the dung they inhabit, factors such as water content, nutritional quality, the presence of parasites & drugs and chemicals given to the animal that excreted it may all contribute.