Types Of Flies In Idaho

Idaho’s mountain streams and high desert create unique habitats for horse flies and deer flies, but the full picture of the Types Of Flies In Idaho is much broader. You might be surprised to learn that over 1,200 fly species call this state home, from the annoying black flies along the Salmon River to the tiny fruit flies buzzing around your kitchen. This guide breaks down the most common flies you’ll encounter, how to identify them, and what you can do about them.

Whether you’re fishing the Clearwater, hiking near Boise, or just trying to enjoy a summer barbecue, knowing your flies helps you stay ahead. Let’s get into the details.

Idaho’s diverse geography—from alpine lakes to sagebrush plains—supports a wide range of fly species. Some are just nuisances, while others bite or spread disease. Here’s what you need to know about the main groups.

Biting Flies You Need To Watch For

These are the flies that make outdoor activities miserable. They bite to feed on blood, and some can transmit pathogens.

Horse Flies (Tabanus spp.): Large, fast, and aggressive. They have patterned wings and big eyes. Their bite is painful and can cause swelling. Found near livestock and water sources.
Deer Flies (Chrysops spp.): Smaller than horse flies, with dark bands on their wings. They buzz around your head and bite exposed skin. Common in wooded areas and near streams.
Black Flies (Simuliidae): Tiny, humpbacked flies that swarm in spring and early summer. They bite relentlessly, especially around the face and neck. Can cause severe itching and allergic reactions.
Stable Flies (Stomoxys calcitrans): Look like house flies but have a pointed mouthpart for biting. They attack ankles and legs. Common around barns and animal pens.
Mosquitoes (Culicidae): Technically flies, these are well-known biters. Idaho has several species, including those that can carry West Nile virus. They breed in standing water.

Non-Biting Flies That Are Still A Problem

These flies don’t bite, but they can contaminate food, spread germs, and be a major annoyance.

House Flies (Musca domestica): The classic gray fly with four dark stripes on the thorax. They breed in garbage, manure, and decaying matter. They carry bacteria and can trigger allergies.
Blow Flies (Calliphoridae): Metallic green or blue flies. They are attracted to dead animals and rotting meat. They can infest homes if a rodent dies in the walls.
Flesh Flies (Sarcophagidae): Gray with three dark stripes on the thorax. They are larger than house flies and often have a checkerboard pattern on the abdomen. They breed in carrion and garbage.
Fruit Flies (Drosophila melanogaster): Tiny, red-eyed flies that appear around overripe fruit, vegetables, and drains. They breed quickly and are hard to eliminate.
Drain Flies (Psychodidae): Small, moth-like flies with fuzzy wings. They breed in the slime inside drains, sewers, and septic tanks. They are weak fliers and often found near sinks.

Flies That Matter For Anglers

If you fish in Idaho, you already know that matching the hatch is critical. Here are the key aquatic flies that trout feed on.

Mayflies (Ephemeroptera): Delicate insects with upright wings. They hatch in large numbers from spring through fall. Key species include the Green Drake, Pale Morning Dun, and Blue-Winged Olive.
Caddisflies (Trichoptera): Moth-like insects that fold their wings over their backs. They are abundant in most Idaho streams. Important hatches include the October Caddis and Spotted Sedge.
Stoneflies (Plecoptera): Large, robust insects with two pairs of wings. They crawl on rocks and are a favorite food for big trout. The Salmonfly hatch in June is legendary.
Midges (Chironomidae): Tiny, mosquito-like flies that hatch year-round. They are crucial in still waters like lakes and ponds. Imitating midge pupae and adults is essential for winter fishing.
Damselflies and Dragonflies (Odonata): Large, predatory insects that live near water. Their nymphs are important food for bass and trout in still waters.

How To Identify Common Idaho Flies

Knowing what you’re dealing with helps you choose the right control method. Here’s a quick identification guide.

Size And Shape

Large (over 1 inch): Horse flies, robber flies, crane flies.
Medium (1/4 to 1/2 inch): House flies, stable flies, flesh flies, blow flies.
Small (under 1/4 inch): Deer flies, black flies, fruit flies, drain flies, midges.

Color And Markings

Gray with stripes: House fly, stable fly, flesh fly.
Metallic green or blue: Blow fly.
Black with clear wings: Black fly, midge.
Brown or tan with patterned wings: Deer fly, horse fly.
Red eyes: Fruit fly.
Fuzzy, moth-like: Drain fly.

Behavior

Bites: Horse fly, deer fly, black fly, stable fly, mosquito.
Swarms around face: Deer fly, black fly.
Buzzing around garbage: House fly, blow fly.
Near fruit or drains: Fruit fly, drain fly.
On livestock: Horse fly, stable fly, horn fly.
Near water: Mayfly, caddisfly, stonefly, midge.

Where You’ll Find Different Flies In Idaho

Different habitats attract different flies. Knowing where to expect them helps you prepare.

Mountain Streams And Rivers

This is prime territory for biting flies like black flies and deer flies, especially in spring and early summer. You’ll also see massive hatches of mayflies, caddisflies, and stoneflies. The Salmon River, Lochsa River, and Payette River are hotspots.

High Desert And Sagebrush

Horse flies are common here, especially near livestock and water tanks. Stable flies can be a problem around ranches. You’ll also encounter robber flies, which are large predatory flies that hunt other insects.

Urban And Suburban Areas

House flies, blow flies, fruit flies, and drain flies thrive in cities like Boise, Meridian, and Idaho Falls. They breed in garbage, pet waste, compost, and drains. Mosquitoes are also a problem in areas with standing water.

Lakes And Ponds

Mosquitoes breed in the shallow edges of lakes and ponds. Midges are abundant in still waters, especially in spring and fall. You’ll also see damselflies and dragonflies near the shore.

How To Control And Prevent Fly Problems

You don’t have to live with flies. Here are practical steps you can take.

For Biting Flies

Use EPA-approved insect repellent containing DEET, picaridin, or oil of lemon eucalyptus. Apply to exposed skin and clothing.
Wear protective clothing: Long sleeves, long pants, light colors, and a hat with a net. Tuck pants into socks in heavy infestations.
Avoid peak activity times: Black flies are worst in early morning and late afternoon. Deer flies are active during the day.
Use fans: Biting flies are weak fliers. A strong fan on a porch or patio keeps them away.
Treat livestock: Use approved fly sprays, ear tags, or pour-ons for horses and cattle. Keep barns clean and dry.
Remove breeding sites: Fill in puddles, clean gutters, and empty containers that hold water. This reduces mosquito and black fly breeding.

For Non-Biting Flies

Sanitation is key: Take out trash regularly. Clean up pet waste. Keep compost bins covered. Wash recycling containers.
Seal entry points: Caulk cracks around windows and doors. Install tight-fitting screens. Use door sweeps.
Use traps: Sticky traps, UV light traps, and bait traps can reduce indoor populations. Place them away from doors and windows.
Clean drains: Pour boiling water or a drain cleaner down sinks to remove the slime that drain flies breed in. Do this weekly.
Store food properly: Keep fruit in the refrigerator. Clean up spills immediately. Store pet food in sealed containers.
Use fly swatters or vacuums: For a few flies, a quick swat or vacuum works. Empty the vacuum bag outside.

For Aquatic Flies (Anglers)

Match the hatch: Observe what flies are on the water. Check local fly shops for hatch reports.
Carry a variety of patterns: Have dry flies, nymphs, and emergers for mayflies, caddisflies, stoneflies, and midges.
Use the right size: Flies range from size 22 (tiny midges) to size 4 (large stoneflies). Carry a range.
Fish during hatches: Trout feed actively when flies are hatching. Early morning and evening are often best.
Learn to read the water: Look for rising fish, splashy takes, and insects on the surface. Focus your casts there.

When To Call A Professional

Sometimes fly problems are too big to handle on your own. Here are signs you need help.

You see large numbers of flies inside your home for more than a week.
You find maggots in your home or near your foundation.
You have a persistent problem with biting flies on your property.
You suspect a dead animal in your walls, attic, or crawlspace.
You have a septic system or manure pile that is attracting flies.

A pest control professional can identify the source, recommend treatments, and apply insecticides if needed. They can also help with exclusion and sanitation.

Frequently Asked Questions

What Are The Most Common Biting Flies In Idaho?

The most common biting flies are horse flies, deer flies, black flies, stable flies, and mosquitoes. Black flies are especially bad in spring near rivers. Horse flies are common in rural areas with livestock.

How Can I Tell A House Fly From A Stable Fly?

House flies have a blunt mouthpart and do not bite. Stable flies have a pointed, bayonet-like mouthpart and bite, usually on the ankles and legs. Stable flies also have a checkerboard pattern on their abdomen.

What Flies Do Trout Eat In Idaho?

Trout eat mayflies, caddisflies, stoneflies, midges, and terrestrial insects like ants and grasshoppers. The specific hatch depends on the river and the time of year. The Salmonfly hatch in June is a major event.

Why Are There So Many Flies Around My House In Idaho?

Flies are attracted to food, moisture, and breeding sites. Common causes include garbage, pet waste, compost, overripe fruit, dirty drains, and standing water. Sealing entry points and improving sanitation usually solves the problem.

Are There Any Dangerous Flies In Idaho?

No flies in Idaho are venomous or deadly. However, biting flies can cause allergic reactions, secondary infections from scratching, and transmit diseases like West Nile virus (mosquitoes). Black fly bites can cause severe swelling and itching in sensitive people.

Understanding the Types Of Flies In Idaho helps you enjoy the outdoors more and keep your home comfortable. Whether you’re dealing with biting flies on a hike or house flies in the kitchen, the key is identification, prevention, and targeted control. Idaho’s fly diversity is just part of living in a state with such varied landscapes. With the right knowledge, you can minimize the annoyance and focus on what matters—enjoying your time in the Gem State.