Exorista mella  Exorista mella is a tachinid fly of the genus "Ezorista" within the family Tachinidae of the order Diptera. They are typically found in the United States and Canada. Within the U.S in the state of Arizona they have been found in both mountainous and agricultural regions. "E. mella" is a parasitoid fly, a polyphagous generalist which parasitizes a variety of hosts. Female "E. mella" flies are selective when deciding on what host to parasitize. Once a host is selected a female may oviposit her eggs on the surface of the host. Larvae then burrow into the host for the remainder of their development usually killing the host once they emerge during either prepupae or pupae stage of development. Experiments in these flies have suggested that they can learn from experience that influence certain behaviors as suggest them as candidates for biocontrol agents to control certain pests. Physical characteristics include having a stigmal plate that is not elevated like their protuberance, as well as a sternopleuron pertaining to the thorax on the lateral side with three bristles. Likewise, behavioral characteristics include their parasitoid tendencies. As parasitoids, "E. mella" typically spend most of their life growing in a host. Unlike other fly species born in a host, in "E. mella", neither sex determination nor sex ratio divergence is related to host size. However, the size of adult "E. mella" is directly correlated with the size of the host from which the fly emerged. Thus, flies that were oviposited and burrowed alone into larger hosts were larger than those that emerged from a smaller host or one that was superparasitized. A study shows that the sex of the emerging flies does not correspond to the host size or superparasitism of the host, though the two factors influence the size of adult flies, and the larger adult flies deposit a larger number of eggs than the smaller ones. Additionally, host larvae activity has a larger impact on parasite oviposition than host larvae size. "E. mella" is commonly found in the United States and in Canada. In Arizona, "E. mella" have been found in the mountainous regions as well as agricultural regions of southern Arizona. On average, the larval development of "E. mella" lasts for 10 days. Larvae emerge from their eggs on the surface of their hosts, after which they burrow into the host for the remainder of their development.