The Flesh Fly: Sarcophaga crassipalpis


            Like all species in the order Diptera, Sarcophaga crassipalpis undergoes a life cycle called complete metamorphosis, which includes four stages: egg, larva, pupa, and adult (2013. Fly...). Spring marks the typical mating season, and fertilized eggs develop and hatch inside the female (Kgware et al.). Once they reach the larval stage, they are most commonly deposited into vertebrate remains or manure, which they will feed off of for nearly a week. When they are ready to pupate, the larvae wriggle away from the food source.  The pupal stage lasts about ten days, during which the pupal body progressively darkens as development proceeds (Diaz & Kaufman 2011). It is during this stage that diapause occurs (see Form and Function). Adults are able to reproduce about once every ten days, but the average lifespan is only around twenty days (Wessels et al. 2011).

            Because of their short lifespan, effective reproduction is imperative. On average, females mate within the first two to four days of adulthood (Hahn et al. 2008). However, all female flies undergo oogenesis – the process of creating eggs – at approximately the same time regardless of whether they have been exposed to males. The size and mass of eggs is also independent of the mating process. Still, mating is more advantageous as females who mate produce a quantity of ten percent more eggs than those who do not (Hahn et al. 2008). This demonstrates the importance of the mating ritual in the flesh fly life cycle. In fact, almost all of a Sarcophaga’s life is spent preparing for and engaging in reproduction.

            The nature of S. crassipalpis raises several reproductive constraints. For instance, the female’s search for carrion to sustain her larvae is not always an easy one.  The quick decomposition of organic matter combined with interspecific competition make animal remains an unstable, sometimes unavailable environment for the flesh fly (Hahn et al. 2008). Furthermore, most females in the wild (as opposed to in laboratory settings) lay only one clutch of eggs due to their short lifespan (Wessels et al. 2011). This increases the pressure to find an adequate location to drop her larvae as she usually only has one chance. Females also require an external source of dietary protein in order to undergo oogenesis (Wessels et al. 2011). In environments where resources are scarce, reproduction is often impossible. Unlike many other species of flies, S. crassipalpis is unable to reallocate non-reproductive resources; however, they are able to produce eggs for almost two weeks after they reach adulthood, which is longer than the average fly. Luckily, oogenesis proceeds at the same rate regardless of when a female receives a protein source, so even flies with scant resources usually have time to seek out an adequate meal (Wessels et al. 2011).

            Although females carry the bulk of the burden of reproduction, males also face conflict when it comes to passing on their genes. Both the physiology and the behavior of the male S. crassipalpis reflect his struggle to find a mate. As in many animal species, the male is significantly larger than the female. Males also possess strong front legs which allow them to more easily dominate females during the mating process (Diaz & Kaufman 2011). (For more on S. crassipalpis physiology, see Form and Function). The male also exhibits behaviors that indicate the significance of his role in reproduction. Males visually evaluate other insects that come nearby and handle threats quickly by attacking both males of their own species and insects of other species. While it is unclear whether this is an innate or a learned behavior, it demonstrates the response of male flesh flies to reproductive obstacles (Paquette et al. 2008).

            Besides the territoriality that males exhibit toward other species of Insecta, S. crassipalpis interacts with a variety of other species. Follow the link to learn more about flesh fly Interactions. Or click here to return to the home page.