Understanding What Attracts Black Flies

← Pest & Insect Control | Insect Repellents & Prevention

Quick answer

• Black flies love damp, cool conditions.
• They’re drawn to carbon dioxide and lactic acid from breath and sweat.
• Moving water is a major attractant; they lay eggs there.
• Dark colors on clothing can make you a bigger target.
• They’re most active at dawn and dusk.
• Avoid areas with lots of vegetation near water during peak season.

What to check first (do this before you drive out)

Before you even think about packing the car, get a lay of the land regarding these tiny terrors.

• Land manager / legality: Who’s in charge? Is this US Forest Service land, BLM, a state park, or private? Knowing this tells you where to find the official rules and advisories. Some areas might have specific recommendations or even temporary closures due to insect activity. Always check the managing agency’s website.

• Access/road conditions: Can your rig even get there? Black flies often hang out near water, and those access roads can get gnarly. A two-wheel-drive sedan might be fine for a paved park road, but a forest service road could demand something with higher clearance and all-wheel drive, especially after rain. Don’t get stuck miles from nowhere with a swarm on your tail.

• Fire restrictions + weather + wind: This is camping 101, but crucial with bugs. Hot, dry weather can sometimes suppress black fly activity, but don’t count on it. High winds can actually be your friend, blowing the flies away. Check the forecast for rain, humidity, and wind speed. And always, always know the current fire restrictions.

• Water plan + waste plan (Leave No Trace): Black flies breed in moving water. This means your campsite might be near their nursery. Think about where you’ll get water and how you’ll dispose of your waste. Pack out everything you pack in. The less impact you leave, the better for everyone, including yourself.

• Safety (wildlife, distance to help, comms): Black flies aren’t dangerous in the way a bear is, but a severe swarm can be debilitating, making it hard to breathe or see. Know your surroundings. How far is the nearest town or ranger station? Do you have cell service? A satellite communicator is a smart move for remote trips.

Step-by-step (field workflow)

Alright, you’ve done your homework. Now, how do you actually deal with them once you’re out there?

1. Scout your campsite:

• What to do: Arrive during daylight. Look for a spot that’s relatively open, not directly in dense woods or right on the edge of fast-moving water.
• What “good” looks like: A clearing with some breeze, a good distance from obvious breeding grounds like streams or marshy areas.
• Common mistake: Picking the first “pretty” spot you see without considering bug habitat. Avoid this by doing a quick scan for standing water or thick, damp vegetation.

2. Set up camp quickly:

• What to do: Get your tent and cooking area established as efficiently as possible.
• What “good” looks like: Tent zipped up, gear stowed, minimal time spent standing exposed.
• Common mistake: Dawdling during setup. The longer you’re out in the open, the more time they have to find you.

3. Apply repellent:

• What to do: Use a repellent with DEET, picaridin, or oil of lemon eucalyptus. Cover exposed skin and clothing.
• What “good” looks like: A consistent, even layer of protection. Don’t forget behind the ears or the back of your neck.
• Common mistake: Skimping on application or missing spots. They will find those gaps.

4. Choose appropriate clothing:

• What to do: Wear light-colored, loose-fitting clothing. Long sleeves and pants are your best friends.
• What “good” looks like: No gaps between your cuffs and gloves, or your pants and boots. A head net can be a lifesaver.
• Common mistake: Wearing dark colors or tight clothing. Black flies are attracted to dark hues and can bite through thin, tight fabric.

5. Manage your breath and sweat:

• What to do: Try to stay cool. If you’re working hard, take breaks in a shaded, breezy spot.
• What “good” looks like: Minimizing heavy exertion during peak fly activity.
• Common mistake: Pushing too hard during dawn or dusk. This creates more CO2 and lactic acid, essentially turning you into a buffet.

6. Cook downwind:

• What to do: Set up your stove so the smoke is blown away from your seating area and tent.
• What “good” looks like: A comfortable cooking experience without a cloud of flies descending.
• Common mistake: Cooking in a spot that traps smoke and bugs. The heat and activity can actually draw them in.

7. Use a fan (optional but effective):

• What to do: A small battery-powered fan can create a breeze around your seating area or tent entrance.
• What “good” looks like: A personal bubble of relative peace.
• Common mistake: Not having one when you really need it. If you’re particularly sensitive, this is worth the weight.

8. Plan activities for midday:

• What to do: Schedule hikes or strenuous activities for the hottest part of the day when flies are less active.
• What “good” looks like: Enjoying your time outdoors without constant irritation.
• Common mistake: Trying to do everything at dawn and dusk. That’s prime fly time.

9. Seal up your tent:

• What to do: Keep your tent zipped at all times. Open it only when necessary and do it quickly.
• What “good” looks like: A fly-free sanctuary for sleeping.
• Common mistake: Leaving the tent flap open while you’re inside. They’re sneaky and will get in.

10. Check your gear before packing out:

• What to do: Do a quick sweep of your tent, sleeping bag, and pack for any hitchhikers.
• What “good” looks like: A clean departure.
• Common mistake: Unknowingly bringing a dozen flies home with you. They can bite inside your car too.

Common mistakes (and what happens if you ignore them)

Mistake	What it causes	Fix
Camping right next to fast-flowing water	Constant swarm, bites, inability to relax or enjoy the outdoors.	Camp at least 50–100 yards away from streams and rivers, preferably in an open area with some breeze.
Wearing dark-colored clothing	Attracts more flies, making you a bigger target for bites.	Stick to light-colored, loose-fitting fabrics. Think tan, beige, or light grey.
Forgetting to apply repellent thoroughly	Bites on exposed skin, leading to itching and swelling.	Use a high-quality repellent and cover all exposed areas, including behind ears and neck. Reapply as needed.
Overexerting during dawn/dusk	Increased CO2 and sweat production, making you irresistible to biting flies.	Pace yourself, especially during peak activity times. Take breaks in shaded, breezy spots.
Not sealing tent zippers properly	Flies getting into your tent, making it unusable as a refuge.	Always ensure zippers are fully closed. Open and close them quickly when entering or exiting.
Ignoring wind direction when cooking	Smoke and heat draw flies to your cooking area, making mealtime miserable.	Position your stove so that smoke is blown away from your campsite and activity areas.
Underestimating the sheer number of flies	Frustration, inability to sleep, potential for allergic reactions in sensitive individuals.	Be prepared. Bring plenty of repellent, head nets, and consider a small fan. Know when to cut your losses and head home.
Assuming flies are gone after sunset	Bites can still occur if conditions are right, especially in humid areas.	Stay vigilant. While activity usually drops, a cool, humid evening can still bring them out.
Not having a plan for heavy infestations	Ruined trip, stress, and potential for bites even through light clothing.	Have backup plans. Know alternative campsites or be willing to postpone the trip if conditions are truly unbearable.
Relying solely on bug spray	Can wear off, and some areas might be too dense for it to be fully effective.	Combine repellent with other strategies: clothing, fans, campsite selection, and timing of activities.

Decision rules (simple if/then)

• If the forecast calls for high humidity and little wind, then postpone your trip because black flies thrive in these conditions and will be miserable.
• If your campsite is directly adjacent to a fast-flowing creek, then move your camp at least 50 yards away because that’s prime breeding territory.
• If you see swarms of flies already around, then apply repellent immediately and consider wearing a head net because you’re already in their zone.
• If you’re planning to hike during dawn or dusk, then wear long sleeves, long pants, and apply repellent because these are peak biting times.
• If you notice flies are particularly drawn to your breath, then slow down your activity level and try to stay in a breezy spot because you’re emitting attractants.
• If your vehicle has low ground clearance, then double-check the road conditions before heading out because muddy or rutted access roads can be impassable.
• If you’re sensitive to insect bites, then bring extra antihistamines and consider a stronger repellent because reactions can be more severe.
• If you’re camping in an area known for black flies, then pack a small battery-powered fan because the airflow can create a personal bug-free zone.
• If you’re cooking a meal, then set up your stove downwind from your seating area because smoke and activity can attract them.
• If the flies are really bad, and you can’t find relief, then it’s okay to cut your trip short because a miserable camping trip isn’t worth it.
• If you are using a tent with mesh windows, then ensure the zippers are fully closed before you enter because they will find any opening.
• If you plan to swim, then be aware that flies can be attracted to you when you get out of the water and are wet and warm.

FAQ

What time of year are black flies the worst?

Black fly season typically runs from late spring through early summer, often peaking in May and June, depending on your region and the weather. They need specific conditions to hatch and mature.

Are black flies dangerous?

While their bites can be itchy and painful, black flies are not generally considered dangerous in terms of transmitting serious diseases to humans in the US. However, severe infestations can be extremely irritating and debilitating.

Do black flies bite through clothing?

They can bite through thin, tight-fitting clothing. Loose-fitting, thicker fabrics offer better protection. Always apply repellent to exposed skin, even if you’re wearing long sleeves.

What does a black fly bite look like?

A black fly bite is usually a small, red, raised bump that can bleed slightly. They tend to be intensely itchy and can sometimes swell significantly.

Can I use natural repellents against black flies?

Some natural oils, like citronella or eucalyptus, may offer some limited protection, but they are generally less effective and require more frequent reapplication than DEET or picaridin-based repellents.

Why are they so attracted to me when I breathe?

Black flies are attracted to carbon dioxide (CO2) that you exhale and lactic acid produced during physical exertion. This is a primary way they locate potential hosts.

Are black flies active at night?

Generally, no. Black flies are primarily diurnal, meaning they are most active during daylight hours, especially during the cooler parts of the day like dawn and dusk.

What’s the best way to deal with them if I’m camping in an area with a known infestation?

Preparation is key. Bring plenty of repellent, wear protective clothing, select your campsite wisely (away from water, in a breezy spot), and consider a head net for added protection.

Will smoke keep black flies away?

Campfire smoke can offer some temporary relief by creating a barrier and potentially deterring them, but it’s not a foolproof solution and doesn’t protect you when you’re away from the smoke.

What this page does NOT cover (and where to go next)

• Specific peak seasons for every state or region (check local wildlife agencies).
• Detailed information on chemical compositions of repellents (consult product labels).
• Medical advice for severe reactions to bites (see a healthcare professional).
• Identification guides for every species of black fly (these vary widely).
• Advanced camping techniques for extreme weather (look for specialized guides).