Springtime flies are parasites of earthworms
The housefly is one type of insect that is almost universally hated. And probably for good reason! Houseflies are called maggots when in the immature stage, and these maggots live in and feed on decaying plant and animal material, including sewage and almost any other yucky stuff that you can think of.
Insects such as the housefly play important ecological roles as recyclers. But we humans generally ignore this positive side to the housefly and leap straight to the conclusion that it is a disgusting insect.
Certainly the food habits of the housefly don't endear the insect to most of us, but the real reason that we should loathe the housefly is because of its ability to transmit disease organisms on its feet. Because of this, the old housefly has been responsible for untold amounts of human sickness, suffering and death through diseases such as typhoid, cholera and dysentery.
Because of our understanding of the relationship of the housefly to the transmission of human disease organisms, we try to keep these insects away from our food. That is why we use window screens to cover open windows and doors. That is why we use fly swatters to kill flies when we can. And that is why we hang sticky flypaper to trap the little six-legged aerial acrobats when they land.
So it is not surprising that flies crawling on windowpanes are not a welcome sight to most people. For sure, that is the case if the flies happen to be on the inside of the window. However, the old fireside poet Oliver Wendell Holmes had a more positive view of seeing a fly crawling on a window. At least, that is the case as recorded in his poem "Spring."
The poem begins "Winter is past; the heart of nature warms." The poem chronicles events in nature that announce that spring has sprung. Such things as leaves emerging on plants and early season flowers. Snakes, frogs and turtles emerging from hibernating sites. Songs of birds returning for the summer.
In Holmes' list of harbingers of spring, he also mentions an insect, the housefly. He writes:
"The house-fly, stealing from his narrow grave,
In the poem, Holmes is describing accurately an early spring encounter many of us have with a fly -- one that somehow is in our homes and finds its way to our windows. Holmes is very accurate in his description of the behavior of the fly, except he is not describing the housefly but a fly that resembles the housefly, one called the cluster fly.
The cluster fly is not only found in our homes but almost any building including hospitals and churches. This fly does resemble the housefly but is somewhat larger, does not have white stripes on the thorax, and when at rest the cluster fly overlaps the tips of its wings, something the housefly does not do. This fly also moves sluggishly and has the habit of making a buzzing noise while it spins around on the floor or windowsill in a fly's version of a break dance.
So what is the cluster fly anyway? This fly spends the winter in sheltered places such as wall voids or attics of homes. Sometimes it is found in very large number in clusters, and that is the basis for the name cluster fly. It is sometimes called an attic fly because that is where it is commonly found.
The cluster fly seeks protected sites for the winter where it hibernates for the cold period -- as Holmes stated, "Drugged with the opiate that November gave." Come the warmer temperatures of spring, the fly comes out of hibernation and seeks the wide-open spaces of the great outdoors. It is at this point that we see cluster flies crawling across windowpanes.
Once outside, the insect will lay eggs in earthworm burrows where newly hatched maggots will find and feed as parasites on earthworms. Cluster flies will complete three to four generations per year with the last generation of adult flies seeking a protected place to spend the winter. This is when they show up at our homes.
So what can be done to keep cluster flies out of our homes? Caulking cracks and openings on the south side of houses will reduce the numbers that get in. For those that do get in, how about smacking them with a fly swatter or a folded newspaper? But finish reading the newspaper before using it to dispatch a fly -- the squashed insect will leave a spot on the daily news.