For those hoping that the past winter's snows and polar vortexes might mean fewer mosquitoes this spring, keep hoping.
The colder weather this year has somewhat delayed development of larvae. But it won't much affect the numbers of adult mosquitoes that'll eventually emerge.
Mosquitoes become lethargic at around 60 degrees and can't function when temperatures are less than 50 degrees. Some females hibernate before the first frost, and some do die when the weather is frigid.
But the eggs they've laid aren't killed in the cold. They're in hibernation, waiting for a warm, wet day in the spring to hatch into larvae. Eggs deposited on moist surfaces can even withstand drying, waiting as long as several years to hatch.
And carpenter ants and termites, other pests that homeowners hate, spent the winter snug underground waiting for a warm day to start munching on your woodwork.
Unfortunately for us, insects are really resilient when it comes to surviving the winter. Some will have an antifreeze-like substance in their body. Some dig deeper in the ground. Some go inside homes.
The bad news for humans is that these bugs, and especially mosquitoes, are adaptable: The water in which they develop can be fresh, stagnant, brackish or polluted, even sewer effluent. It might be in a wetland or salt marsh but it also can be in a puddle, creek, tin can, horse trough or abandoned swimming pool.
Much of the eastern half of the United States gets 30 or more inches of precipitation a year. And this year, normal or higher amounts of rain and snow have fallen in most of those areas.
That means more spots for larvae to hatch, more chances for an egg that has been dried out for a couple of years to wake up and get ready to rumble.
The winter cold does not kill many mosquitoes because all the mosquitoes that we have been survivors since the ice ages and before. We've had colder periods in the past. So they are still around, and they are still thriving.
Another reason not to get your hopes up: One strain of mosquito-borne disease is named La Crosse encephalitis after the city in Wisconsin. Encephalitis is an inflammation of the brain.
If there's plenty of water available, standing water around, then the number of breeding sites that are available for mosquitoes increases, and we'll have a bigger crop of mosquitoes.
A mosquito can go from egg to adult in as little as a week and a half, depending upon the species and temperature.
While a mosquito bite is annoying because of the welts caused by an allergic reaction humans have to the females' saliva, public health officials are most concerned with mosquitoes because they can transmit diseases present in blood.
- In fewer than 10 years, West Nile virus has swept across the country with no vaccines to prevent infection and no medicines to treat the disease, which can cause meningitis, an inflammation of the lining of the brain and spinal cord, or encephalitis. Mosquitoes also can transmit the disease to horses, cats, dogs and birds.
- Several variants of encephalitis viruses — including Eastern equine, La Crosse and St. Louis — can be transmitted to humans, and Eastern equine is fatal a third of the time. In horses, Eastern equine encephalitis is almost always fatal.
- In the past five years, Florida had its first reported cases of dengue fever in 75 years from people who had not traveled outside the U.S. One of four related viruses that mosquitoes can carry causes dengue, and dengue's high fever can sometimes develop into dengue hemorrhagic fever, which can kill.
- Heartworm, a type of roundworm that is not a risk to humans, can kill dogs and cats if not treated and has spread to portions of every state except Alaska.
But a bonus from the delay of warm weather — mosquitoes, like people, love it in the 80s — could be a shortened mosquito season and more time for state officials to bring out aerial sprayers and trucks to apply a bacterial insecticide that disrupts larvae growth.
- Change the water in outside pet dishes and birdbaths at least weekly to break a mosquito's development cycle.
- Cover any rain barrels with screens that do not have holes that can allow mosquitoes to come in and lay eggs.
- Check roof gutters once a season to make sure they are not holding water. Look for other items in your yard, too, such as flower pots that may hold water and stow them away from wet weather.
- Place Bt donuts, a floating briquette that releases Bacillus thuringiensis var. israelensis for 30 days, into ornamental ponds or other water sources that can't be drained. The bacteria isn't toxic to people, pets and wildlife but kills mosquito larvae.
- Remove trapped water from tarps placed over wood piles, boats and pools.
For more information on exterminating mosquitoes, contact EHS Pest in Norwood.