'Friendly' flies not friendly to caterpillars

I find it amusing how false rumors start and spread, and those that you may hear regarding the outdoors are no different. Take, for example, when coyote populations and range (also called brush wolves and coydogs) first started expanding in the state. Rumors were flying that the NYS Conservation Department, at the request of auto insurance companies, was "stocking" them to help control the abundant deer that were creating too many car-deer accidents.

A few decades later, it was mountain lions that were being stocked by the State, again to help control overabundant deer herds. This year, the rumor making the rounds involves all the oversized houseflies that are so numerous. Again, the credit is being attributed to the State, releasing them via helicopters to help control the bumper crop of forest tent caterpillars that are munching the leaves from our area's trees this year.

Basically, what is occurring is a common phenomena in nature - when a certain species' population or habitat grows or peaks cyclically, there can be an almost equal or opposite effect on certain other species. Case in point is the expansion of coyotes into New York. As abandoned farmlands were naturally replaced by thicker, heavier vegetation, the habitat created was more suitable to the wild canids. That same habitat change was responsible for increased deer densities, which offered the coyotes increased prey opportunities via fawns and winter-yarded deer. Conversely, this habitat change negatively affected the once numerous pheasant population. The appearance and continuing increase in black bears in our region is, again, the result of habitat changes favorable to the bruins.

The increased presence of the large flies we're seeing this year is directly tied to the cyclic peak in forest tent caterpillars since these oversized "house flies" – often called "friendly flies" – feed on the caterpillars. More available prey supports more predators. It's as simple as that. Ironically, these flies are also sometimes called "government flies" due to the rumors that the government releases them to feed on the caterpillars, which is undoubtedly the basis for the local stories being spread this year.

Scientifically, these flies are "Sarcophaga aldrichi," and resemble houseflies but are larger, slower and distinctly more bristly. Adult flies are gray in color and are 6 to l2 mm long. The sides of their "faces" are hairy, each end of their two antennae has a single and branched bristle, their thoraxes have three black stripes, and their abdomens are checkered.