Some flys are nuisances, some pests and some are like bees. Photo from Purdue University.

By John Woodmansee
Agriculture/Natural Resources Extension Educator, Purdue Extension Whitley County 

WHITLEY COUNTY — The 1860s song of this title has retained some popularity through the years. Who has not been annoyed by a fly sometime in their life? Maybe you’ve tasted “Shoofly Pie,” known for its molasses and sweet, sticky filling.

John Woodmansee

Some flies are nuisances, some are pests, and some mimic bee behavior. Today, I’ll cover a few of the common flies we encounter in Indiana, as explained by Purdue University experts.

Small flies and gnats are small nuisances. The types of small flies that pose a concern for food include fruit flies, phorid flies, moth flies, sphaerocerid flies, and cheese skippers. Measuring about 1/8 inch or so, these flies can be found in moist organic matter, such as decaying fruit and vegetables, garbage, drains, or soil contaminated with sewage.

Cheese skippers are attracted to meat and cheese. If you have houseplants, moist potting soil may provide a suitable environment for fungus gnats. Fungus gnats can resemble tiny mosquitoes. Their larvae can damage plant roots and can transmit fungal pathogens to plants. Inspect any newly purchased plants for small gnats flying around before bringing them into your home.

When repotting, avoid reusing old potting soil. Both fungus gnats and shore flies can cause problems for commercial greenhouse operators.

Nuisance flies include cluster flies and face flies. Both are medium-sized, measuring about ¼ inch or larger. Cluster flies are parasites of earthworms and are strongly attracted to light. Face flies are typically found around cattle farms and breed in fresh cow manure. Neither of these flies poses a problem in structures for most of the year, but they can find their way into houses in late fall. Some of the flies you remove from light fixtures may belong to one of these species.

Filth flies include house flies, blow flies, bottle flies, soldier flies, and flesh flies. All these are medium-sized flies, measuring about ¼ inch in length. They are commonly associated with garbage and filth. These flies play a crucial role in decomposing animal carcasses and serve as a food source for many other animals.

All except the flesh fly breed in decaying organic matter. House flies are strongly believed to spread disease-causing organisms. Typically, these flies enter buildings from the outdoors, originating from places such as dumpsters, trash cans, rodent traps, attics, crawl spaces, or dead animals.

Black flies and biting midges are annoying little pests that can bite humans. Neither are known to transmit disease agents to humans in the U.S. They can be bothersome for livestock, poultry, and wildlife.

Biting midges will also bite pets and are known by names such as “no-see-ums” or “punkies.” Black flies lay eggs in flowing water, while biting midges lay eggs in moist environments and require aquatic or semi-aquatic habitats to develop. Only the females bite; males have mouthparts that cannot bite.

Deer flies and horse flies are annoying flies. I cannot use enough angry adjectives or invectives to express my personal disdain for deer flies. They can be relentless. The bites of female deer and horse flies (males have weaker mouthparts incapable of biting, and do not feed on blood) are painful. To date, there is no conclusive evidence that they are capable of transmitting disease agents to humans, with one exception.

In the western U.S., there is evidence that suggests a deer fly was involved in the transmission of a bacterium that causes tularemia, also known as “deer fly fever” and “rabbit fever.” Deer flies and horse flies are large flies, ¼ to .33 inches and ½ to 1¼ inches long, respectively. They have mouthparts that include two pairs of cutting “blades” that lacerate skin, causing bleeding that the females lap up.

Only females take a blood meal. Female horse flies feed primarily on large mammals, including their namesake, horses. Female deer flies typically feed on moving hosts, and usually bite on the shoulders and head. Deer flies can also feed on birds and reptiles. Species of both flies tend to develop in natural habitats, and some species may develop in low areas of pastures, standing water in fields, or heavily saturated soils.

Unfortunately, there is very little you can do to control or repel deer flies and horse flies. Mosquito repellent doesn’t even work very well. Use clothing and hats to cover exposed skin.

One “actor” in the world of flies is the hover fly. These flies tend to be most numerous in late August and early September. This beneficial yellow and black fly acts like a hovering bee, and some incorrectly identify it as a “sweat bee.” The typical fear of being stung is completely unwarranted, as these flies do not have stingers, nor do they bite. They also wiggle their abdomens up and down after they land, intimidating the novice observer into thinking they are preparing to sting. Hover flies are beneficial because they help pollinate plants, and in their immature stage (larvae), they eat aphids that can be pests on many types of plants.

For more information, access multiple Purdue Extension publications on flies at edustore.purdue.edu. The above material was sourced from these publications, written by various Purdue University experts.