Where they hang out: These chronic outdoor-party crashers can be found near lakes, marshes, lagoons, pools, or any other body of water. (No-see-ums, those barely visible gnats, gravitate to the same soggy places.)
What attracts them: Body heat and moisture, which they need to lay eggs and feed young. “There’s a saying—water plus seven days equals mosquitoes,” says George Hamilton, chair of entomology at Rutgers University, in New Brunswick, New Jersey.
Their kryptonite: Insect repellents that contain DEET work well on individual bugs (see Your Biggest Bug Questions, Answered for more info). To keep swarms away, twice a week empty any standing water in birdbaths and kids’ toys or pet bowls that have been left out in the yard.
What else you need to know: They are at their worst at sunrise and dusk. Notify public-health officers about rain-filled pools on foreclosed properties; they will empty them to prevent the spread of mosquito-borne West Nile virus.