By Mayda Nathan, insect ecologist
DC’s mosquitoes are enough to drive a person crazy. Abundant and stealthy, they make enjoying the DC summertime a real challenge, and they can transmit some nasty diseases, to boot. But they’re a natural part of this swampy environment, probably playing some underappreciated but pivotal ecological role, so we should accept their annoying presence at our barbeques and in our gardens…right? Wrong.
As an insect ecologist, I have a dark fascination with these maddening fellow residents of our city. Over the years that I’ve lived here, I’ve read about our mosquitoes, talked to experts, and participated in a local monitoring program. I’ve run into many misconceptions about who these critters are, what they’re doing here, and the ways we can protect ourselves and stay sane during the summer months.
Misconception #1: There’s just one kind of mosquito in this region.
In North America, we have about 200 species of mosquito. A very small fraction of those bite humans (and, of those that do, it’s only the females who do the biting). There are 30+ different species of “DC mosquitoes.” They all depend on standing water to reproduce, but the type of water they want varies – for some species, only saltmarshes will do, while others insist on ephemeral pools in woodsy settings. Some species prefer the sorts of little pools of water that us humans are great at (unintentionally) providing, like in the form of abandoned tires and clogged gutters. Those are the species we tend to encounter most often in our neighborhoods.
Misconception #2: Mosquitoes are a natural part of this region’s ecosystems.
Yes, there are native mosquitoes here, but most mosquitoes in your DC yard are relative newcomers to the regional ecosystem. The most abundant, irritating mosquitoes in DC neighborhoods are of one species: Aedes albopictus, AKA the Asian tiger mosquito. As its name implies, this species is not from around here. Accidentally imported to North America sometime in the 1980s, the Asian tiger mosquito has taken a liking to its new digs and is now found throughout eastern North America, even becoming the most abundant mosquito in some cities.
We also have several non-native Culex mosquitoes in our midst (though they don’t seem to reach the same aggravating densities as the Asian tiger). Additionally, we have a new arrival. In 2011, Aedes aegypti, the yellow fever mosquito, was discovered in Capitol Hill.
Misconception #3: Bats and other predators in DC depend on mosquitoes for food.
Wouldn’t it be great if we could conscript our bat, bird, and spider friends to wage war on mosquitoes, on our behalf? Alas, while this may be true in wetlands and boreal zones, there is very little support for this idea in urban settings.
Bats in the DC area, for example, are almost certainly not mosquito-eating machines, hoovering up thousands of mosquitoes every night. For one, the Asian tiger mosquito is a day-flier, so its odds of encountering bats are low. Secondly, our bats probably focus their efforts on more rewarding insect prey; mosquitoes are like flying celery sticks, compared to the winged cheesesteaks that are moths and katydids. This is likely the case for many predators in our region; they will eat a mosquito but would probably rather eat something else.
Misconception #4: There’s no environmentally friendly way to control mosquitoes.
I get it – some of our past efforts to control mosquitoes, in the form of large-scale wetland drainage and DDT spraying, had environmental repercussions that are haunting us still. But there are quite a few things you and your neighbors can do to keep from getting bitten, and even to reduce the number of mosquitoes around your house, that have minimal impact on other species.
Defense tip 1: Protect your skin.
There’s an endless array of products that claim to repel mosquitoes, but only a very small number have repeatedly been shown to be effective. I’m only advocating for products that have stood up to rigorous scientific scrutiny. The consistent winner is DEET, followed closely by picaridin (a synthetic version of a molecule found in pepper plants). Oil of lemon eucalyptus has been shown to be effective, but it must be re-applied more frequently than DEET (every 6 hrs v. every 10 for DEET). Also, throw out your citronella sprays and candles. That stuff’s useless.
Defense tip 2: Stagnant water is the enemy.
Start by removing ALL standing water around your house – what the pros refer to as “tip-‘n-toss.” Asian tiger mosquitoes can breed in amazingly small quantities of water, so no potential container should go overlooked. In my neighborhood, some common sources are:
Trash and recycling cans with broken or missing lids; submit a request through DC 311 to have yours fixed/replaced, and in the meantime, drill a small hole in the bottom.
Those accordion-style gutter extenders that direct water away from a house; pop a nylon knee-high over the end to keep the mosquitoes from going inside.
In-ground drain lines; secure a piece of window screening over the opening to keep mosquitoes out.
If your yard has a fountain or something similar that you can’t empty, pick up some mosquitofish (Amazon will ship you live ones!) or Bti dunks or Bti bits. These latter products contain a strain of bacteria that are toxic to mosquitoes and a few close fly relatives, but are harmless to everyone else – you, your dog, birds, bees, butterflies, etc.
Defense tip 3: Go on the offensive – but spray only if you must.
If removing standing water and using an effective repellent don’t keep the mosquitoes at bay, you still have a few options – from the passive to the nuclear.
Gravid Aedes Traps, or GATs. These nifty contraptions use water to lure in female mosquitoes who are looking for a spot to lay their eggs. There’s a big caveat: the traps are only effective if most contiguous neighbors deploy them. It won’t hurt if you’re the only one on your block who has GATs in your yard, but it won’t help much, either. On the plus side, areas with more than 80 percent of households using GATs have seen remarkable declines in mosquito numbers.
Some commercial spraying companies offer “natural,” “garlic-based” alternative to insecticides. This product doesn’t kill mosquitoes; it merely repels them. Online reviews are positive. But it is pricey and needs to be applied frequently.
Commercial spraying operations – the nuclear option. If you’re pregnant or expect to become pregnant, or have an infant or someone else in your household who’s immunocompromised – that is, if someone in your home is particularly at risk from mosquito-borne diseases like West Nile virus or Zika – then you might want to consider this option. It works, but it works because it’s a serious pesticide being applied to the vegetation and foundation around your house.
* In order to preserve insect biodiversity, consider making commercial insecticide treatment of your property a last-choice option. The treatment often involves pyrethroids – a group of compounds that are generally safe for mammals and birds (yay), and that don’t stick around long in the environment (yay), but that are highly toxic to a broad swath of insects (boo). For effective mosquito-killing power, pyrethroids are sort of the least-bad option, but using them will wipe out a lot of the wonderful, harmless insect biodiversity you might otherwise get to experience in your yard.
Go forth, armed with mosquito knowledge, to enjoy your porch beers, barbecues, and backyard play dates. Hopefully this information will help keep you sane and healthy all summer long.
Mayda Nathan is completing her PhD at the University of Maryland, where she studies insect ecology. She has lived in Washington, DC for ten years, and loves the city – mosquitoes and all.