4 Types of Flies in Delaware: From Garden Pests to Backyard Pollinators
September 28, 2026
Not every fly buzzing around a Delaware backyard is the same insect wearing a different disguise. Some sip nectar and pollinate garden flowers, some raid onion beds, and at least one variety has earned a reputation for ruining beach days along the coast. Understanding the different types of flies in Delaware helps homeowners, gardeners, and beachgoers know which species to tolerate, which to manage, and which to simply admire from a distance.
This look at four common Delaware flies covers a picture-winged garden visitor, the fly most people picture when they hear the word “fly,” a biting marsh dweller with a fierce summer reputation, and a gentle pollinator that mimics bees without any of the risk. Each species has its own habits, habitat preferences, and role in the local ecosystem.
| Fly Type | Size | Bite Risk | Typical Habitat |
|---|---|---|---|
| Black Onion Fly | 1/4 to 3/8 inch | None | Gardens, fields, meadows |
| Common Housefly | About 1/4 inch | None | Homes, trash areas, livestock zones |
| Greenhead Fly | About 3/4 inch | High (females only) | Coastal marshes, beaches |
| Hoverfly | Varies by species | None | Flower beds, gardens, meadows |
1. Black Onion Fly
The black onion fly (Tritoxa flexa) belongs to the picture-winged fly family, a group known for the striking markings on their wings. The black onion fly is a medium-sized, black, picture-winged fly measuring about 1/4 to 3/8 inch. Three white bands cross each black wing, with two of the three stripes prominent while the third sits closer to the body and can be harder to spot when the wings are closed.
Black onion flies are found in landscapes, fields, and meadows. Historical entomology records note that this native species has been recorded in New Jersey, though it has mainly drawn attention as a pest in the Ohio Valley and Midwest states rather than farther east or south. That history means Delaware gardeners along the mid-Atlantic coast may spot the species in smaller numbers than growers in states like Ohio or Indiana, but it remains a fixture of onion and garlic beds throughout the region.
Onions, garlic, and other members of the Allium family are the only host plants listed for the black onion fly, and adults probably sip flower nectar. The adults drink flower nectar, but the larvae, or maggots, are plant eaters that feed on onion and garlic bulbs and use them as shelter during winter. Gardeners growing ornamental Allium alongside edible onions should watch both, since edible onions and ornamental onions are both susceptible to maggot damage.
The larvae are easy to misidentify. The maggots of the black onion fly resemble house fly maggots and can be separated from other species only by host data and microscopic characters. Anyone dealing with fly larvae in a vegetable patch or comparing notes with growers researching different types of flies used for fishing bait will notice how many maggot-stage insects share this generic look.
By the time black onion fly maggots are found damaging an ornamental Allium, it is too late to save that plant, so protecting the rest of the bed usually means spraying foliage with a pyrethroid insecticide before adults lay eggs. Rotating onion and garlic crops each season also reduces the odds of a repeat infestation the following year.
2. Common Housefly
Few insects are as universally recognized as the housefly (Musca domestica). It possibly originated in the Middle East and spread around the world as a commensal of humans. That long partnership with human settlements explains why it turns up in nearly every Delaware neighborhood, farm, and food-service kitchen.
The type of fly which Delaware residents and business owners notice during the spring, summer, or fall is typically the common housefly. Physically, adults are gray to black with four dark, longitudinal lines on the thorax, slightly hairy bodies, a single pair of membranous wings, and red compound eyes set farther apart in the slightly larger female. Pest control specialists in the region echo those details: a certified entomologist at Viking Pest describes this type of fly as a quarter of an inch long with a gray body, six legs, and two wings.
Houseflies rarely limit themselves to polite feeding habits. These pests will eat out of trashcans, off of animal carcasses, and will also land on food for a snack. That indiscriminate diet is exactly why they’re considered a hygiene concern rather than just a nuisance. Their small size makes it possible for them to get into a home or business through a crack in the door or a hole in a screen.
Pro Tip: Repairing torn window screens and keeping trash bins sealed does more to reduce housefly numbers indoors than any spray, since these flies rely on easy entry points and exposed food waste to thrive.
Pet owners dealing with flies that bother animals rather than food should note that houseflies are only one piece of the picture; a closer look at the types of flies that bother dogs reveals several biting species that behave very differently from this common household visitor.
3. Greenhead Fly (Biting Horse-Fly)
Few insects generate as much summer complaint along the Atlantic coast as the greenhead. Tabanus nigrovittatus, also known as the greenhead fly, is a species of biting horse-fly commonly found around coastal marshes and wetlands on the east coast of the United States. The scientific name Tabanus nigrovittatus refers specifically to this salt-marsh species, distinct from other horse flies found farther inland.
Timing matters if you’re planning a Delaware beach trip. The adult flies are most active in July but they can be found all the way up to September, according to Rutgers University’s Department of Entomology and Economic Zoology. Only one sex causes the trouble people remember: the adults feed on sugary substances for energy, while female flies feed on blood during the time they lay their eggs, similar to how female mosquitoes require blood. The female flies will attack any source near them, whether it’s humans, livestock, or other insects.
Weather plays a bigger role in greenhead activity than most beachgoers realize. Wind direction plays a huge part in the reason why greenhead flies are seen at beaches in New Jersey and Delaware. A steady onshore breeze tends to keep the insects pinned closer to the marsh grass, while calm or offshore conditions let them drift toward the sand.
Delaware has actually pioneered a low-tech solution to the problem. In Delaware, the use of three to five traps near isolated human dwellings has resulted in almost complete reduction in greenhead attacks. The design is simple but precise: the traps use separate legs 40 inches long, with the box fastened so its lower edge sits 24 inches above the ground, because the greenhead fly usually flies at about this altitude. The trap is painted a glossy black to contrast with its surroundings and absorb heat from the sun, with a top made of metal insect screen.
Pro Tip: Since greenhead traps rely on glossy black surfaces and precise height, a homemade box trap 24 inches off the ground near a marsh edge can noticeably cut down bites without any chemical spray.
Anyone comparing coastal biting insects to inland species researching the types of flies found in North Dakota will notice how differently regional fly populations behave depending on whether they breed in salt marsh mud or freshwater habitats.
4. Hoverfly (Flower Fly)
Not every fly in a Delaware garden deserves a swat. Hoverflies, members of the family Syrphidae, are frequently mistaken for bees or wasps despite being completely harmless. Hover flies, with their yellow markings, resemble wasps or bees but do not bite or sting. One common eastern species, the margined calligrapher (Toxomerus geminatus), shows the classic black-and-yellow banding that fools so many observers into backing away.
Hoverflies, sometimes called flower flies or syrphid flies, make up the insect family Syrphidae, and as their common name suggests, they are often seen hovering or nectaring at flowers, with adults of many species feeding mainly on nectar and pollen while the larvae eat a wide range of foods. That larval diet varies by species, and in some species the larvae are saprotrophs, eating decaying plant and animal matter in the soil or in ponds and streams. Other hoverfly larvae feed on aphids, making them useful allies for gardeners battling infestations without pesticides.
Their ecological value goes beyond a single garden bed. Hoverflies are important pollinators of many wild plants, in some cases as important as bees, and bring some of the highest pollen loads per visit to flowers of certain plant species. Some researchers rank them even higher in the pollinator hierarchy: syrphid flies are frequent flower visitors to a wide range of wild plants and agricultural crops and are often considered the second-most important group of pollinators after wild bees.
Delaware gardeners hoping to attract more hoverflies alongside butterflies can plant flat, open blooms that make nectar easy to reach. Those interested in the broader pollinator picture in the state may enjoy a companion look at the butterflies found throughout Delaware, many of which share the same flower beds as hoverflies without competing for resources.
- Look for a wasp-like yellow and black pattern combined with only one pair of wings — true wasps have two pairs.
- Watch for hovering flight, where the insect holds a fixed position in midair before darting sideways.
- Check for large, rounded eyes that nearly meet at the top of the head, a trait true wasps and bees lack.
Telling these four species apart takes practice, but the payoff is worth it. A gardener who can distinguish a black onion fly from a hoverfly knows exactly which one needs foliage protection and which one deserves a spot near the tomatoes. Beachgoers who recognize a greenhead by its size and marsh-edge timing can plan trips around calmer wind days, while anyone dealing with a housefly problem indoors knows the fix usually starts with a sealed screen door rather than a bottle of spray.