Mosquitoes need about a week of standing water to go from egg to biting adult, which is why a once-a-week walk around your yard does more than swatting ever will. Fairfax County's Health Department and Arlington County both point to the same handful of places: gutters, downspouts, tires, birdbaths, plant saucers, tarps and anything else that can hold water for a few days without you noticing.
A mosquito's life cycle from egg to flying, biting adult takes roughly a week when there's standing water available, according to Fairfax County's Health Department. That means a container that's been full since last weekend's rain is already a potential source by the time you get around to checking it — unless checking is already part of your routine. Weekly is the interval the county recommends, not "after it looks like it's been a while."
Walk the yard once a week and look at:
This list overlaps closely between Fairfax County's and Arlington County's own guidance, so it's a fair one to work from no matter which side of the region you're in.
Some water is meant to be there — a rain barrel, a water feature — and can't just be dumped. For those, both counties point to larvicides made for mosquitoes, such as Bacillus thuringiensis var. israelensis, sold as "dunks." Follow the product label for how often to add a new one. Arlington's own guidance describes mosquito dunks as harmless to birds, fish, wildlife and pets when used as directed — worth knowing if you're hesitant to add anything to a rain barrel or pond. Covering a rain barrel with a fine screen is the other option, so mosquitoes can't reach the water to lay eggs in the first place.
Not routinely. Fairfax County's Health Department says directly that it does not spray for nuisance mosquitoes, and that adult spraying happens only under exceptional circumstances. The county's main approach is source reduction — encouraging residents to remove standing water — plus targeted larviciding in known problem areas, not neighborhood-wide spraying.
If you're being bitten in your own yard and can't find the source, Fairfax County's Health Department offers a free yard mosquito inspection on request: call 703-246-2201 or email [email protected]. No equivalent free inspection program for Arlington County residents was found as of this writing — if you're in Arlington, start with the checklist above and consider a pest-control service if the problem persists.
Fairfax's Health Department has noted that, going back to 2004, the county's first mosquito pools testing positive for West Nile virus each year have typically turned up between early May and early July, with the season generally running into late October. That's a wide window, which is really the point: the weekly habit matters more than any single calendar date.
Most mosquitoes are most active at dusk and dawn, but Fairfax County's Health Department notes one common exception worth knowing: the Asian Tiger mosquito, which is also active during the day. That's the one you're likely to notice while doing yard work in the afternoon, not just on an evening walk. It doesn't change the weekly checklist, but it's a reason not to assume you're safe from bites just because it's the middle of the day.
Standing water is easy to miss because most of it isn't obvious — it's the saucer under a planter, not a puddle in the driveway. Pair your weekly check with whatever yard work is already on your calendar. If you haven't given the deck its warm-weather once-over yet, deck care before summer covers checking furniture covers and low spots for standing water too.
For everything the checklist turns up that's bigger than a five-minute fix — clogged gutters, an overgrown yard hiding containers, or a pond that needs real attention — book yard cleanup, outdoor cleaning or landscaping with an independent local Pro.
Last updated September 2026.
About a week. Fairfax County's Health Department says mosquitoes need roughly a week of standing water to develop from egg to biting adult, which is why checking your yard weekly — not just after it rains — makes the difference.
Yes. Fairfax County's Health Department offers a free yard mosquito inspection on request, at 703-246-2201 or [email protected]. No equivalent program was found for Arlington County as of this writing.
Not for general nuisance mosquitoes. Fairfax County's Health Department says it doesn't spray for nuisance mosquitoes and only does adult spraying under exceptional circumstances — source reduction (removing standing water) is the main tool.
A larvicide made for mosquitoes, such as Bacillus thuringiensis var. israelensis, sold in dunk form. Follow the label instructions, and cover rain barrels with a screen where you can instead of relying on larvicide alone.