The Common Yellow Dung Fly (Scathophaga stercoraria), is one of the most familiar and abundant of flies in many parts of the northern hemisphere. As its common name suggests, it is often found on mammal faeces, most notably that of horses and cows.
From 5 mm to 11 mm in length. The adult males of Scathophaga stercoraria are bright golden-yellow with orange-yellow fur on the front legs. Females are a little duller in colour, with pronounced green-brown tinges, and lacking the bright coloured fur on the fore legs. It is a very variable species, and part of this may be climate driven.
The adults are mostly predators on smaller insects , they will also feed on pollen, but most specimens seen on flowers will be hunting prey there. Both males and females are found on dung, the males only feeding on other insects that visit dung, such as blow-flies. Females will be there both to feed and oviposit on the dung surface.
Females prefer to lay their eggs on the small hills of the dung surface and avoid depressions and pointed parts of the dung. This ensures survival, as emergence is better by avoiding the drying on small points in the dung. Also by avoiding possible drowning by rain by not laying eggs in depressions of the dung surface. The female yellow dung-fly is capable of making these decisions about her egg placement, and thus increasing possibility of success of her future generations. The eggs hatch into predatory larvae and feed on insect larvae within the dung. After 21 days or more of feeding, dependent on conditions, the larvae burrow into the soil around and beneath the dung and then develop into pupae, before developing into adult flies.
Scathophaga stercoraria can produce four or five generations per season. The adults are active throughout much of the year in most moderate climates. In most cases both males and females will mate multiple times, as is very common in insects. Much has been studied about the competition between genders and what factors determine mating success, and what part that in turn may play on the competitive nature on the larvae.