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What to do about biting flies

Mosquitoes are out now, take
steps to protect yourself. 
Photo:Jeff Hahn UMN Extension
Regardless where you live in Minnesota, the odds are very good that you are encountering at least one kind of biting fly right now. The two most common are mosquitoes and black flies. While they are irritating, there are steps you can take to minimize their annoyance.


Mosquitoes are common throughout the summer, but they are particularly abundant  after rainy weather.

Reduce numbers of black flies & mosquitoes!

First, make sure you are not producing any mosquitoes on your own property. Drain potential breeding sites for mosquitoes, such as buckets, tires, cans, children’s’ swimming pools or even clogged gutters.

 Any type of shallow, undisturbed standing water, with a little bit of organic material, is a great place for mosquito larvae.

If possible, avoid being outside when mosquitoes are most common. This is typically during the morning and evening. Of course, they can still bite anytime during the day if we are close enough to their resting sites around grassy and brushy areas.

Personal protection is the best way to protect yourself from mosquitoes. Covering up with long-sleeved shirts, long pants, and socks and shoes is an option. Whether you do that or not (let’s face it, summer its shorts season), the best personal protection against mosquitoes is the use of repellents.

Repellents that really repel the bugs! 

The most effective and long lasting repellent is DEET (N,N diethyl m toluamide). It comes in different concentrations. However, DEET concentrations over 35% does not really increase protection. Do not apply more than 30% DEET on children and infants at least two years old.

There are several alternatives to DEET. The Centers of Disease Control and Prevention (CDC) lists several EPA registered active ingredients:
  • Picaridin
  • IR3535
  • Oil of lemon eucalyptus (OLE)
  • Para-menthane-diol (PMD)
  • 2-undecanone
Use a repellent to protect
yourself against mosquitoes.
 Photo: www.scjohnson.com
Whichever repellent you choose to use, always follow all label directions so the product is used most effectively and while minimizing potential hazard to safety. For more information on mosquito repellents see the CDC – Protect yourself and your family from mosquito bites page.

Do 'bug zappers' work?

And if you are thinking of putting your faith in gadgets such insect electrocuters (aka bug zappers), mosquito traps, or ultrasonic emitting devices, don’t. Research does not show these devices can effectively reduce mosquito bites.

Similarly, don’t rely on purple martins or bats to take care of your mosquito problems. They actually feed on few mosquitoes, preferring larger insects, such as dragonflies, butterflies, crane flies, beetles.

What to do about black flies, gnats, buffalo gnats 

And if mosquitoes are not enough for you, black flies (also called gnats or buffalo gnats) are also active now in many sites in Minnesota.

Black flies are stout, humpbacked, dark-colored flies. The larvae live in rivers and streams. The adults are good fliers and can be found miles from where they emerged. They are most common during early morning and early evening as well as when it is cloudy.
Black flies are small but pack a painful bite.
Photo: Jeff Hahn, UMN Extension

While they will bite anywhere exposed skin, they particularly like flying around the head and biting along the hairline and ears. Even if they are not biting, they are still annoying when they fly around person’s face.

It is challenging to avoid black fly bites.  When possible, avoid the times when black flies are most common. Wear clothes to cover bare skin, like long-sleeved shirts, long pants, socks and shoes, and hats.

Unfortunately, repellents, like DEET, are not consistently effective against black flies. You do not have much to lose by using one but understand that you may not get good results.

Author: Jeffrey Hahn, University of Minnesota Extension



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