Q.  Can mosquitoes develop indoors? I thought they needed water, but we keep getting bitten in our house even though all the windows are closed and the AC is on. We don’t have a real mosquito problem outside, just inside!

A. Yes, mosquito larvae do develop in standing water, and the standing water needs to contain some kind of organic material for the larvae to feed on. For that reason, although mosquitoes can get into a building, they rarely breed and develop inside a building. But it can happen in unusual circumstances.

Several years ago we dealt with a mosquito problem at an old apartment property. Residents of building 110 were getting bitten by mosquitoes outside the building and also inside the building. We couldn’t find any standing water on the grounds and residents of adjacent buildings had no mosquito complaints. The 50-year old brick apartment buildings had attached boiler rooms that were no longer in use and had been blocked off. This is where we found our breeding mosquitoes.

In building 110, the huge boiler room was 100 by 50 feet and 30 feet high and most of the boiler room was below ground level. We discovered that an underground spring had been slowly feeding water, now 2 to 3 feet deep, into the boiler room. One small window near the ceiling allowed mosquitoes and debris to get into the water which was teeming with mosquito larvae and pupae. The emerging adult mosquitoes then found their way out of the boiler room either through the window or up into the connecting apartment building. The building’s residents were literally sitting on top of an indoor mosquito swimming pool.

In your case, however, you need to think about unseen areas of standing water that could be in your home. In my own home, I once had mosquitoes breeding inside a potted plant container. The plastic pot with drain holes had been placed inside a prettier ceramic container. This plant was the last stop in my search for the cause of our indoor mosquito bites. When I pulled the plastic pot out, there was about an inch of dirty water in the bottom of the ceramic pot—and plenty of mosquito larvae and pupae! Somehow a single female Asian tiger mosquito found her way into the house, probably fed on one of us, then managed to find that single source of standing water in which to lay her eggs!

Other possible indoor breeding sites for mosquitoes are unused floor drains such as in laundry rooms or basements, shower drains in bathrooms that are rarely or never used, or sump pump pits. Also check drip pans in dehumidifiers or under refrigerators or AC units. Even a half-full bucket of dirty water in the laundry room or a pet water dish left in the basement can breed mosquitoes if the right circumstances exist.