Organic Answers Column - May 7, 2025 - Mosquitoes
Flood Water Mosquitoes Are Different
There will be times when the mosquitoes are more numerous and aggressive that they defy the normal precautions we have learned to take. Tipping water from plant saucers, scattering mosquito dunks and granules around moist spots on the patio - that isn't enough to tackle some that are out there in the environment waiting for a triggering event to send them into the world.
North Texas experienced heavier than normal rainfall in the late summer of 2022, saturating the soil to such a level that it triggered the hatch of a particular type of mosquito that isn't your usual "garden variety" nuisance. These were bigger and more aggressive insects than the normal pests we struggle to keep out of our houses and yards every year. They weren't there because your mosquito traps failed or you didn't put granules in the saucers under your outdoor potted plants. They were awaiting release from higher ground.
Not found in the usual wet spots around the landscape, these mosquitoes were dormant in the dry soil, possibly for several years, waiting for the right conditions to flood the land, saturating it enough so they could hatch. This large mosquito, Aedes vexans, is called the "Flood Water Mosquito" that is released from the surrounding landscape where the eggs were laid the last time there was a flood or very heavy rain event.
As described by the CDC, "Immediately following a hurricane, flooding occurs. Mosquito eggs laid in the soil by floodwater mosquitoes during previous floods hatch. This results in very large populations of floodwater mosquitoes. Most of these mosquitoes are considered nuisance mosquitoes." They don't tend to spread more disease, but they are larger and aggressive. So that's why yardwork in the dusk and dawn hours can be so difficult after a particularly wet episode.
Photo from Montana State University
One area where they have been studied is the Greater Yellowstone Ecosystem. From the Montana State Universtiy website comes this:
Aedes vexans is a floodwater mosquito that is very common in the Greater Yellowstone Ecosystem. The adult female bites preferably cattle and humans during the day as well as in the evening and night. Both females and males feed on nectar, honeydew, and sap. Females typically lay their eggs after a blood meal in areas associated with standing water. The adult form of this species can be found from May through October.
From a pest control site called VDCI, that specializes in these pests, comes this information: "By floodwater, it means that they lay their eggs individually on moist soil above the waterline at a wide variety of aquatic habitats, including temporary pools such as detention ponds or irrigated fields, but also permanent water bodies where the water level fluctuates. They especially prefer to lay eggs where there is a lot of leaf and twig cover, helping to keep the soil moist. After a short period of drying, the eggs must subsequently be flooded with water to hatch. During periods of drought, eggs can remain dormant but viable for many years, waiting for the water to rise."
Don't be fooled by the photo of the flood water mosquito (Aedes vexans by Katje Schultz via CC) resting on a flower; they are aggressive biters and go after humans and pets. (More information linked below.)
AccuWeather story (photo by Alain Hogue)
Aedes vexans Montana State University Entomology Group / Insects of Yellowstone
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