Biting Insects: What Works and What Doesn’t?

There’s a lot of conflicting advice about warding off biting insects. We’ll try almost anything to avoid becoming a meal, but what actually works? And, what can we learn about biting insects that helps us avoid them?

In North America, mosquitoes, black flies, deer flies, horse flies, and stable flies are our common attackers. Each one responds differently to repellents and our attempts to cover up.


In Eastern Canada, mosquitoes are most active in the month of June. But, you’ll find them in diminished numbers throughout the summer months. Peak hours are dawn and dusk, but expect to see them throughout the day.

Mosquitoes enjoy cool and shady areas like forests. They depend on stagnant calm waters like ponds and puddles to lay their eggs. If you have problems with mosquitoes near your home or cabin, try emptying any standing water on your property. Bird baths, buckets, and tires provide breeding grounds for them.

Mosquitoes are attracted to the carbon dioxide that we exhale, heat from our bodies, dark clothing, and scents from deodorants, perfumes, and other cosmetics. This is also true for all the biting insects on this list.

Mosquitoes use their proboscis to draw blood. The proboscis looks like an elongated needle. It can penetrate your skin and through your clothing. However, covering up with pants and long-sleeved shirts will offer some protection.

Lucky for us, mosquitoes are vulnerable to many types of bug repellents. DEET, picaridin, and oil of lemon eucalyptus works especially well on them.

A woman walks away from the camera with hundreds of mosquitoes following her.
That’s me getting attacked by mosquitoes on a June camping trip in Gatineau Park. Mosquitoes, unlike many biting insects, can penetrate through clothing. Covering up will help prevent some bites, but dark colours (like the ones I’m wearing here) can attract them.

Black flies

Peak black fly season is May and June. If you are hitting the trails at this time, expect to be dealing with both black flies and mosquitoes. Black flies love hot and humid weather and are most active in the daytime hours.

They rely on moving water from rivers and streams to lay there eggs. The drying up of seasonal creeks and rivers contributes to their decline in mid to late summer.

Unlike mosquitoes, who use a proboscis to penetrate the skin, black flies cut your skin with their mouth-parts and lap up the blood. This makes their bites more painful, but they cannot bite through clothing. Anecdotally, I’ve never been bitten by them in confined areas, like a tent, either.

Steady breezes deter these weak flyers. Bug repellents containing DEET also work, but with less success than against mosquitoes.

Deer and Horse Flies

There are several similarities between deer and horse flies, so I’ve lumped them together in one category. Both are active in the warmer summer months and die down towards the end of August.

Deer and horseflies are active during daytime hours. You’ll find them near swamps, marshes, and the edges of forested areas. They do not like dark and shady places, so you might be able to avoid them by seeking shelter in the shade. Though, that hasn’t always been effective for me.

Both deer and horse flies have a powerful bite – the worst of the biting insects on this list. However, they cannot bite through tightly woven clothing. According to Orkin, “deer flies prefer to attack a moving host, while horse flies prefer to attack a stationary host.”

Deer and horse flies are persistent hunters. They will circle their prey until they find a safe place to land. If you’ve ever been followed by them, you know how annoying this can be! Trying to swat or run away from them only makes the problem worse by attracting more of them.

In addition to dark colours, carbon dioxide, warmth, and scent, these flies are attracted to shiny surfaces. For example, the shiny quality of water draws them in and makes them a nuisance to swimmers.

Unfortunately for us, repellents do not work well against them. So, it’s best to cover up. You can also take advantage of their attraction to shiny things by using duct tape and deer fly patches to trap them. Put the tape on the top of your hat and circling flies will be drawn to it and become stuck.

Stable flies

Stable flies are active in July and August. They love bright light and warm weather and are most active in the daytime hours.

If you’ve been around stables, you’ve probably seen them targeting the ankles and legs of cows and horses. Provided the opportunity, they’ll feast on us too. They breed in moist grasses, seaweeds, and wet straw.

Stable flies can fly many miles without exhausting themselves even in windy conditions. This annoys paddlers who can’t escape them, even when they are far from shore.

Once again, insect repellents aren’t very effective. The best thing you can do is to cover up, especially your ankles and lower legs. Some paddlers bring a bug swatter along with them to kill stable flies. They are much too fast to kill by hand.

What Works


When dealing with biting insects, one of the best things we can do is cover up. Lightweight and breathable long sleeved shirts and pants will help keep you safe. Hats work well to prevent insects from biting the top of your head.

When insects are really bad, you’ll want bug netting to cover your head and neck. Some fishing outfitters even sell gloves to protect your hands from being bitten.

You can treat clothing with permethrin to ward away mosquitoes (and ticks). It will offer minimal protection against black flies, deer flies, horse flies, and stable flies. You can also buy clothing already treated with it. It will last several washes.

Insect Repellents: Effectiveness and Toxicity


Research shows that common bug repellents like DEET (N,N-Diethyl-meta-toluamide), picaridin (icaridin), and oil of lemon eucalyptus are effective in the right concentrations on skin and clothing. Permethrin is also effective, but it cannot be used directly on the skin.

Concerns About Toxicity

There are valid concerns about the toxicity of insect repellents and the harm they do to us and the environment. I try to use these products sparingly and I don’t enter the water after applying them.

DEET is slightly toxic to fish, birds and aquatic invertebrates. Picaridin is toxic to salamanders and permethrin can harm bees and fish. Further studies are needed to understand how repellents affect the air, soil, and water. In the meantime, it’s clear that these products should be used sparingly and we should be careful not to pollute waterways with them.

As for their effect on us, check out this Canadian Government website for a list of bug repellents and their safe concentrations. Safe concentrations often vary by age, so check before using them on children.

A recent study shows that sunscreen increases the permeation of some insect repellents, so avoid mixing them. Check out Made Safe for more details about the safety and environmental concerns of insect repellents.

What Not to Do

It’s hard not to, but scratching insect bites will worsen the itch by increasing inflammation. Itching can also lead to secondary infections by introducing bacteria. The best thing to do is keep the skin disinfected and avoid scratching.

A woman's leg is covered in many swollen mosquito bites.
Yikes! I swell up like a balloon from mosquito bites. Swelling is caused by your body’s reaction to the saliva of biting insects. Some people react more than others. For some, bug bites can cause serious allergic reactions.

Ultrasonic repellents do NOT work against biting insects despite manufacturers’ claims. In fact, one study showed that electronic mosquito technologies actually increased the biting rates of mosquitoes. Another study showed no difference at all, so don’t waste your money.

Patches and wristbands, often marketed towards parents who are fearful of using chemical sprays, do not work. Even when these products use effective active ingredients, they are not in high enough concentrations to protect you.

Other Useful Resources

For a more detailed analysis of different bug sprays and their effectiveness, check out Consumer Reports.

The Weather Network has a bug report for many provincial and national parks. You’ll find it below the forecast section.

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4 comments on “Biting Insects: What Works and What Doesn’t?

  1. “…but they cannot bite through clothing and they won’t bite in confined areas like a tent.”

    Absurd! I’ve had plenty of black flies bite through clothing, socks, shirts, an inside a car.

    • Hi! Are we talking about the same black fly? All the research I’ve read suggests they cannot bite you through clothing – that’s because of how female black flies mouths’ are designed to lacerate the skin. That said, they are very adept at getting under clothes by crawling through openings. Writing about it makes me itch – I hate the feeling of them crawling around the neckband of my shirts. This is why folks recommend tucking in clothing and avoiding button-up shirts.

      As for confinement, I’ve never been bitten by a black fly in a tent, enclosed hammock, or vehicle. But, there’s not much research that I can find on that, so perhaps that is anecdotal. I’ve updated the article to reflect that. That said, researchers in Algonquin Park had a lot of trouble getting female black flies to bite in a lab. They would bite a few minutes after being captured, but quickly seemed to turn off from that behaviour. Suggesting that black flies change their “behavioural mode” away from host seeking after confinement. That doesn’t necessarily translate to the real world experience you are describing though. I wonder if it’s more likely that someone is bitten by a black fly in a tent or car immediately after being enclosed.

  2. If deer flies can’t bite through clothing then how did I get 7 bites within 3 weeks in areas that are covered?

    • Yikes! I should have said tightly woven clothing because it seems that deer flies can get through some materials. Bug jackets are always a safe bet, but not always desirable. I find they get quite sticky and warm in hot weather. I hope you don’t have to endure any more bites this season.


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