|Click on the photo to better see the pollen on the wings.|
As bothersome as flies can be, I am often surprised by both their beauty and their benefits. The tachina fly is no exception. Just from this photo, one can see that the tachina fly is a pollinator. While in search of nectar, it is easy for this hairy fly to become covered in pollen. According to Wikipedia, this can be beneficial in higher elevations where there are significantly fewer bees.
Another benefit to this fly is the fact that the larvae of this fly are internal parasitoids of certain other pest insects. Stink bug and leaffooted bug families are favourite host targets for this fly. Specifically, squash bugs and green stink bugs. The process is a bit gruesome, but not everything in nature is rainbows and butterflies. There are a variety of ways that the tachina fly gets its larvae inside the host victim. Some flies lay their eggs on leaves that are ingested by other insects like caterpillars, butterflies or moths. This tachina fly (the female can lay about 100 eggs) deposits a single egg on its vicitm. The egg is very sticky and cannot usually be removed from the host without killing it. Once the egg hatches, the larva (or maggot) then bores directly into its host, where it will live off the interal juices for a few weeks while it grows. By the time it is ready to emerge from its host, the maggot will have grown to the size of the body cavity of its victim. Once it emerges, the host insect finally dies, and the cream coloured maggot starts a pupation phase about an inch underground. Two weeks later, the adult fly will emerge.
For more information on this fascinating fly, check out the following websites: