Feature Article - for release the week of  June 22, 2008

Roxanne Connelly - Extension Entomologist  & Dan Culbert - Extension Horticulture Agent

 

You don’t See ’em, but you Sure Feel ‘em!

Those that spend time out of doors are fondly remembering the dry weather of a few weeks ago.  Ranchers, gardeners, fishermen and anyone who spends time in the Great Outdoors has probably noticed that those unwelcome seasonal visitors have finally arrived.

When soils become moist and temperatures rise, these small mosquito relatives fly out of the wetlands, looking for a little sip of blood.  They can’t be seen, but they sure can be felt, with sharp biting pain whenever folks are outside, especially at dawn and dusk.  Locals call them no-see-ems, but University of Florida Entomologists are likely to identify these as biting midges.

Biting midges can be a nuisance to anyone who spends time outdoors during early morning and evenings.   Even during the daytime on still, cloudy days they will readily inflict irritating, painful, bites.   For some, their feeding can cause long-lasting painful lesions on exposed skin.

 

The Invisible Life

Biting midges are sometimes incorrectly referred to as sand flies, but true sand flies are a different group on insects.  Besides mosquitos, another group of flies that can appear under current weather conditions are non-biting blind mosquitos that go by the local name of “chizzywinks”. (I wrote about these critters a few years ago – contact us if you want to see that article.)

There are over 4,000 species of biting midges.  One genus, Culicoides, has over a thousand different species world-wide, with 47 species known in Florida.  (Click here to see more photos of biting midges.)   Some are commonly fond of certain habitats; any visit to Florida salt marshes will produce welts from many different kinds of no-see-ems.

The eggs are very small – about 0.25 mm long – and laid on moist soil.  Some species can lay up to 450 eggs per batch and as many as seven batches in a lifespan. Eggs typically hatch within two to 10 days of being laid, depending on the species and temperature.  

Larvae are worm-like, creamy white, and 1/16” to 1/8” [2-5 mm] long.  Some of the larva of tropical species live in rotting fruit, bromeliads, and other water-holding plants. Other larval habitats include mud, sand, and debris at edges of ponds, lakes and springs, treeholes, and slime-covered bark.

Local species typically feed on small organisms close to the water’s surface. The larval stage can last from two weeks to a year, depending on the species, temperatures, and geographic area.

A sixteenth-inch-long female biting midge, Culicoides sonorensis, feeds blood delivered through artificial membrane developed for mass insect rearing. Photo by Scott Bauer, USDA/ARS

 

The resting pupa of these midges is pale yellow to light or dark brown. During this 2-3 day resting period, these insects change into airborne biting midges. As they emerge, the new adult males and females both feed on nectar.  But the females will be looking for blood primarily around dawn and dusk – required for her eggs to mature.  

Adult no-see-ums are gray and less than 1/8 inch long. Their two wings are hairy and have color patterns that help to identify species.  If you are able to see one up close, their large compound eyes more or less cover the entire front of their head above their antennae.  The mouthparts have cutting teeth for blood-sucking in females, but not in males.

Biting midges are primarily a nuisance.  The major medical issue associated with them is allergic reactions to the bites. However, like other blood feeding flies, some Culicoides species carry pathogens that can cause disease in humans and animals.  One species [C. sonorensis] can transmit the bluetongue virus, a serious disease of sheep and cattle. (Request the new UF fact sheet on Bluetongue:  http://edis.ifas.ufl.edu/IN768)

 

Living with these Invisible pests

On a large scale basis, efforts to reduce no-see-ums involve either flooding or draining wetlands and the use of chemical pesticides. Currently, larval habitats of biting midges are not targeted in public control efforts because lots of area would need to be drained or flooded to result in reduced no-see-ems.  Likewise some negative environmental impacts would also be the result.

Using pesticides against adult no-see-ems is not efficient. It would mean daily insecticide applications, and this will be expensive and may harm the environment.

Bite prevention is the preferred way of dealing with these pests. Around the home, if you can’t (or don’t want to) stay indoors at dawn or dusk, try using special screening to exclude these flies from porches and homes.

Most biting midges can pass through 16-mesh insect wire screen and netting, so a smaller mesh size is required (i.e., choose a screen with a larger mesh number to get smaller holes to keep out no-see-ums.) 

Since smaller mesh screens limit air flow, an alternative is to treat screens with a long-lasting insecticide that will be fatal to the no-see-ums that land on the screen.  Another option is to use fans to keep them away.

Jonathan Day, left, and Roxanne Rutledge, entomologists with UF/IFAS , hold vials containing biting midges at UF's Florida Medical Entomology Laboratory in Vero Beach.  Photo: Marisol Amador,UF/IFAS

Removal traps for limited no-see-em relief in isolated areas use CO² as an attractant; they lure the biting midges to an insecticide-treated target.  Research from the UF/IFAS Florida Medical Entomology Laboratory showed no-see-em populations were reduced for short periods of time.  However this method is expensive and best used by where pest control personnel

So if you are going to be out with the bugs, wear protective clothing and use insect repellents.  Choose lighter colored garments and those with long sleeved pants and shirts.  Consider hats with fine meshed netting.

Insect repellents containing DEET typically are also labeled for use against no-see-ums.  There are some new repellents that may be tried – please request the UF bulletin on mosquito repellents http://edis.ifas.ufl.edu/IN419 for the latest research on these products.  Use them before exposure to the biting midges, and apply according to the label.

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on biting midges (a.k.a. no-see-ums), please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 3 PM on Tuesday afternoons. GO GATORS!

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Trade  names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean. Last update: 06/18/2008.  This page is maintained by Dan Culbert