In East of Eden, John Steinbeck describes flies as a “final and malicious burden” on the body of a character who had just died. While this is among the important ecological functions that flies perform, it is not easy for most of us to find them anything but burdensome.

Consider cluster flies. These are the sluggish, clumsy groups of flies that suddenly appear in numbers, seemingly out of nowhere, in the sunlit corners of our windows or attics during the winter months. One wonders where these insects might have suddenly come from, making us rethink the possibility of spontaneous generation.

It is the mild weather and their life cycle that allows them to emerge from dormancy on warm, sunny winter days like we had last weekend. Cluster flies, also called attic flies, spend their off-season overwintering in protected areas such as vegetation, stone and rock structures, and in the cracks, crevices and voids of our homes. While hidden for much of the winter season, temperatures of 50 degrees will allow them to emerge from their hiding places.

David Sedaris described flies as “disease carriers who feasted upon the dead and then came indoors to dance upon our silverware.” This cannot be said of cluster flies which do not transmit

diseases of concern to humans and, in fact, want little to do with us or our silverware. It is earthworms that should be worried about cluster flies. Cluster flies deposit their eggs in soil near the burrows of earthworms. After a few days, the eggs hatch and larval cream-colored maggots crawl forth looking for live earthworms to parasitize by burrowing into and then consuming the worms for nourishment. The next stage for those fully fed larvae is to pupate and then emerge as adult flies. Don’t ask what happens to the earthworms.

Adult cluster flies are larger than houseflies and have unique markings and features that will help you to identity them. Look for golden hairs on the thorax of cluster flies that make them appear to have a golden sheen. Checkerboard black and silver markings on their abdomen are observable, and their wings will overlap when they are at rest. Contrast that to houseflies whose wings don’t cover each other.

Behavior is also an indicator. These clustering flies move slowly and can be found on their backs spinning aimlessly while trying to right themselves. Their lack of speed makes catching or killing them a breeze. Swatting them is easy, but can result in a strongly scented and oily stain, whose smell has been compared to buckwheat honey, thus another alias, buckwheat flies. For those that prefer not to kill them, vacuuming and releasing them outside is also an acceptable solution to remove them from your domicile. Be sure not to leave any dead fly bodies around your house as they will attract carpet beetles leading to another pest problem.

With the return of cold weather, those flies will head back to their seasonal sanctum and give us a bit of a reprieve. They will, however be back to disgust and disturb us. As poet Suzy Kassem tells us, “Birds are the eyes of heaven, flies are the spies of hell.”

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.