Rain floods the dry ground where floodwater mosquitoes deposited eggs. Containers in the yard also all refill at once when it rains, so the mosquitoes hatch in great numbers, very quickly.
If you live on the Front Range, you’ve probably noticed this happens in the summer. After a run of dry and pleasant weeks, there’s a big afternoon thunderstorm. About a week later, the yard is suddenly full of mosquitoes. There’s a reason for that.
Two things happen when the rain hits. The first involves floodwater mosquito species, which are the dominant nuisance biters across much of Colorado. These species don't lay eggs in water. What they’ll instead do is lay them on damp soil in low ground, ditches, swales, irrigation margins, and floodplains, and those eggs sit dry, sometimes for months or years, waiting. A heavy rain or an irrigation overflow floods that ground, and the eggs hatch essentially at once, in enormous synchronized numbers. That's a batch of larvae rather than a batch of adults, and they need several days to a week or so to develop, which is exactly the delay people observe.
Meanwhile, every container in the yard refills. Perfectly innocuous things like wheelbarrows, plant saucers, sagging tarps, gutters, and corrugated downspouts can become mosquito nurseries in about a week. It doesn’t help that in July, the water is warmer, allowing cold-blooded mosquitoes to mature faster.
For your part, what you can do is dump and scrub every container outdoors weekly. This removes the eggs that are cemented above the waterline. Clear the gutters as well since those are notoriously bad about giving mosquitoes a place to hatch. If irrigation is causing water to pool in your yard, see to it that it’s fixed. And if the problem persists, consider having a professional treat the foliage where adult mosquitoes rest during the hot, dry parts of the day.
If mosquitoes surge in your yard about a week after every storm, Mosquito Squad of East Denver can help. Mosquito Squad treats the shaded areas where mosquitoes rest and points out the breeding sites on your property. This will help you protect your yard with up to 90% reduction in mosquito activity on a recurring 21-day cycle.
