Scathophaga stercorari

Appearance

"Scathophaga stercoraria" is sexually dimorphic, with an average lifespan of one to two months. The adult males are bright golden-yellow with orange-yellow fur on the front legs. Females are a little duller in color, with pronounced green-brown tinges, and no brightly colored fur on the front legs. The adults range from 5 to 11 mm in length, and the males are generally larger than the females. The physical features of separate "S. stercoraria" populations can vary greatly, due in part to the range of locations in which the species is found. Generally, they are located in cooler temperate regions, including North America, Asia, and Europe. They may also favor higher altitudes, such as the Pyrenees and Swiss Alps.Females have paired accessory glands, which supply lubricants to the reproductive system and secrete protein-rich egg shells. Sperm is received in a large structure called the bursa copulatrix, and is stored in a structure called the spermatheca. "Scathophaga" species have three spermathecae,, each with its own narrow duct that connects it to the bursa. Sperm can be stored in the spermathecae for days, weeks, or even years, and sperm from several males can be stored simultaneously.
Males have two projections, the paralobes, which are used to hold onto a female during copulation. Between the paralobes is the intromittent organ, the aedeagus, which transfers sperm into the female's bursa copulatrix.

Behavior

During copulation, sperm is not directly deposited into sperm-storing organs. Ejaculation occurs in the bursa copulatrix, and then females actively move sperm into the spermathecae using their muscular spermathecal invagination to pump sperm into transit. This gives females a level of control over which and how much sperm enters her system, an example of cryptic female choice. Although current results are inconclusive regarding whether or not females are cryptically selecting for a better phenotypic match, a female may benefit from having variable sperm fertilizing her offspring. Such adaptations are advantageous because females benefit from being able to control which sperm are successful in fertilizing eggs. The females may not be aware of which sperm are better suited for her offspring, but simply that being able to control the proportion of sperm from multiple mates can maximize the possibility of an optimal phenotypic match. It is to her advantage to have multiple males' sperm reach her eggs, rather than just one.
After copulation, females prefer to lay their eggs on the small hills of the dung surface, avoiding depressions and pointed areas. This survival strategy aims to prevent desiccation and drowning so the eggs are placed where they have the greatest chance of surviving.The eggs that the female lays on the dung hatch into larvae after 1–2 days, depending on temperature. The larvae quickly burrow into the dung for protection and feed on it. At 20 °C, larvae undergo three molts over five days, during which they grow exponentially. After growth, larvae spend another five days emptying their stomachs before pupation, where no additional body mass is gained. After 10–20 days, the larvae burrow into the soil around and beneath the dung and pupate. The time needed for the juvenile flies to emerge can vary from 10 days at 25 °C to 80 days at 10 °C or less. The smaller females typically emerge a few days before the males. The fitness of the resulting juveniles is greatly dependent on the quality of the dung in which they were placed. Factors affecting dung quality include water content, nutritional quality, parasites, and drugs or other chemicals given to the animal.
Yellow dung flies are anautogenous. To become sexually mature and produce viable eggs or sperm, they must feed on prey to acquire sufficient proteins and lipids. Females under nutritional stress will have higher rates of egg mortality and less survival of offspring to adult emergence. "S. stercoraria" females can then produce four to 10 clutches in their lifetimes. The adults are active throughout much of the year in most moderate climates.

Reproduction

"Scathophaga stercoraria" breeds on the dung of many large mammals, but generally prefers fresh cattle dung. The operational sex ratio on these pats is very male-biased and competition is high. Females are small and have limited precopulatory choice. Copulation lasts 20–50 minutes, after which the male attempts to guard the female from other males. Both males and females often mate with multiple partners. Reproductive success depends on a variety of factors, including sperm competition, nutrition, and environmental temperature.

Food

The adults mainly prey on smaller insects, mostly other Diptera. They can also consume nectar and dung as additional sources of energy. In a laboratory setting, adult "S. stercoraria" can live solely on "Drosophila" and water. Females spend most of their time foraging in vegetation and only visit dung pats to mate and oviposit on the dung surface. Both males and females are attracted to dung by scent, and approach dung pats against the wind. Males spend most of their time on the dung, waiting for females and feeding on other insects that visit the dung, such as blow flies. In the absence of other prey, the yellow dung fly may turn to cannibalism. The larvae are coprophagous, relying on dung for nutrition.

Predators

As well as being an easy meal for a great many bird and bat species, these flies are also preyed upon by other insects. Much competition exists between larvae of different species within a dung pat. Other insect species may also use the pats as hunting grounds. These include robber flies and clown beetles.