Mosquitoes can breed in a patio drain when water sits in it. A drain that empties after a storm gives them nothing to work with. One that holds water under the grate, or backs up behind leaves and grass clippings, can raise a new batch of biters in 7 to 10 days. In Southwest Florida, where afternoon storms refill everything that holds water, the drains are worth a look on the same day you tip out the saucers. For the full lineup of what a service visit can cover, see our pest control services page.
If you would rather skip the detective work, get a mosquito control estimate for your yard.
Can mosquitoes breed in a patio drain?
Yes, if the drain holds standing water. They need very little of it. UF/IFAS Extension Sarasota County’s Managing Mosquitoes fact sheet says mosquitoes need just a bottlecap’s worth of water to complete their life cycle, and it lists ditches and gutters among the places to check.
The EPA’s fact sheet on stormwater structures and mosquitoes explains why drains matter. Catch basins, the sumps under storm drains, hold standing water by design, and the EPA says they need maintenance so debris does not build up in the grate or the storage area and let mosquitoes breed. The same sheet says the aquatic stages of many mosquito species need 7 to 10 days in calm, standing water. A patio or yard drain with a basin below the grate is worth checking for the same reason.
The CDC’s Aedes mosquito life cycle page says a mosquito egg takes 7 to 10 days to develop into an adult. The UF/IFAS guide Mosquitoes and Their Control (2019) says the larvae of the southern house mosquito, found in all Florida counties, turn up in habitats with high organic content, including catch basins and ditches. A drain clogged with rotting leaves can fit that description.
Which drains and wet spots to check
Start with anything that holds water after the rest of the patio has dried. These are the usual suspects, each tied to a source:
- Drains with a basin or sump under the grate. The EPA says catch basins hold standing water by design. Lift the grate and look.
- Gutters and downspouts. The UF/IFAS guide says to clean out roof gutters so leaves do not clog the drain and hold water. The Florida Department of Health’s Protect Your Home From Mosquitoes sheet says roof gutters collect fallen leaves and water, and to clear them monthly.
- Low spots that pool after rain. The UF/IFAS guide says to check for areas that pool and stay wet after rainfall, and to make sure they can drain well.
- Open pipes and vents. The CDC’s home mosquito control page says to cover open vent or plumbing pipes with wire mesh that has holes smaller than an adult mosquito.
- Decorative rocks and plant cups. A UF/IFAS news report on container mosquitoes names decorative rocks with depressions that hold rain or irrigation water, along with bromeliad tanks and tree holes.
How to check a drain for mosquito larvae
You can confirm a breeding drain in a couple of minutes with a flashlight.
- Lift the grate or cap where you can do it by hand. Look for standing water, leaves, sludge or grass clippings below it.
- Shine the light on the water and watch. The UF/IFAS guide calls larvae “wrigglers” because they swim with an S-shaped motion, and says they come to the surface to breathe through a siphon.
- Tap the edge and look for “tumblers.” UF/IFAS says pupae dive and tumble through the water when disturbed, and that the pupal stage generally lasts about two to three days. Pupae mean adults are close.
- Check again after the next storm. A drain that empties between storms does not give larvae the 7 to 10 days of standing water the EPA describes.
Pro tip: Do the drain check on the same day as your weekly container walk. The CDC’s routine is to empty and scrub, turn over, cover or throw out anything that holds water once a week, and a grate is one more thing on that list.
What to do about a drain that holds water
Get the water moving or get the debris out. The fix depends on why the drain holds water.
- Clear the grate and basin. Pull out leaves, clippings and sludge, then flush it so it empties. The EPA ties breeding in catch basins to debris in the grate and storage area.
- Keep clippings out of drains. For all of Sarasota County, the UF/IFAS Extension Sarasota County fertilizer and landscape summary says no grass clippings or yard debris may go into stormwater drains, ditches or roadways. Blow them back onto the lawn.
- Screen what you cannot close. Use wire mesh over open pipes and vents, per the CDC.
- Treat water you cannot dump, by the label. The CDC says to use larvicides on large bodies of water that will not be used for drinking and cannot be covered or dumped out, and to always follow label instructions. For larger containers or standing water that can’t be emptied, the Sarasota fact sheet points homeowners to a bacterial mosquito larvicide sold as bits or dunks, used according to the label. Only use a product labeled for mosquito larvae, read and follow the label, and store it out of sight and reach of children and pets. Treat only water on your own property. For a pond, lake or ditch you do not own, contact your county mosquito control program.
What not to do: don’t stop at the drain. A clean drain helps, and the saucers, toys and gutters around it still count. Our list of seven water-holding spots around a patio covers the rest.
When the drain is not the problem
If your drains stay dry and you still have mosquitoes, the source is somewhere else. A street storm drain belongs to the local stormwater system, and the EPA says local authorities should inspect and maintain those structures. Many Florida counties run tax-funded mosquito control programs, according to the UF/IFAS guide, and the Florida Department of Agriculture and Consumer Services keeps a directory of them.
Screens are the other half. Our guide to screens and standing water covers keeping mosquitoes out of the house once you have cut down where they breed.
When to call a pro
Call a pro when you have cleared the drains, dumped the containers, and the patio is still unusable at dusk. Waves Pest Control services Sarasota and Venice for mosquitoes. For help at your home, start with mosquito control in Sarasota or mosquito control in Venice. For a number before anyone comes out, get a mosquito control estimate online.
Frequently Asked Questions
Can mosquitoes get in through drains?
Open pipes and vents are on the CDC’s list: it says to cover open vent or plumbing pipes with wire mesh that has holes smaller than an adult mosquito. Window and door screens in good repair matter too.
Can mosquitoes breed in a pond?
Yes, if the water stays still. UF/IFAS suggests aerating ornamental ponds or stocking them with fish, and UF/IFAS Extension Sarasota County says to ask Sarasota County Mosquito Management about free mosquitofish.
How fast can a drain produce mosquitoes?
The CDC puts egg to adult at 7 to 10 days. Some eggs wait longer: the CDC says Aedes eggs can survive drying out for up to 8 months, so scrub containers, don’t just rinse them.
