Hordes of Mosquitoes Left in Harvey’s Wake

Editor’s Note: The following article appeared on Mike Merchant’s blog, “Insects in the City,” which can be found at http://insectsinthecity.blogspot.com. The blog offers readers news and commentary about the urban pest management industry and is excerpted here with permission of the author.

Hurricane Harvey continues to leave its mark on Texas. Besides the giant cleanup, hordes of mosquitoes are now descending in many areas. Several pictures are making the rounds on social media, including here and here.

The mosquitoes in those picture are probably in the genus Psorophora, (sore ROFF oh ruh) one of our largest, most painful and aggressive biters. Psorophora mosquitoes have some impressive chops when it comes to survival. One of the so-called floodwater mosquito species, they lay their eggs on land rather than water like most mosquitoes. But not just on any land–eggs are laid at the edges of receding floodwaters, where they will re-hydrate and hatch during the next large rain event.

Because Psorophora are opportunists, taking advantage of brief rainstorms, they must have a quick lifespan. The larvae of floodwater species like Psorophora are the speediest growers of all mosquitoes. They need as little as 3 to 3.5 days of standing water to pass through the four molts common to mosquitoes. The pupal stage has even adapted to survive and complete its development on the mud surface of drying puddles.

What we see in these pictures is evidence that floodwater mosquitoes had already primed the pump when Harvey hit the upper Gulf coast two weeks ago. When the rains came, previously laid eggs hatched across thousands of square miles of coastal prairie and marsh, and billions of Psorophora larvae raced through a quick childhood.

Add to this the scope of the disaster. Harvey’s unprecedented rainfall impacted over 400 miles of Gulf shoreline, dumping an estimated 27 trillion gallons of water. The city of Houston doubled it’s previous all time monthly rainfall record with 39.11 inches (and Houston gets lots of rain). With some 400 miles of Gulf coast prairies producing mosquitoes, I suspect the number of mosquitoes flying around the state right now is also unprecedented.

So don’t be surprised to read and hear lots of mosquito stories over the next couple of weeks. If you have to be out and about in this part of Texas, there is protection you can carry. For extreme conditions a mosquito head net will be necessary. Wear light colored, tight knit, long-sleeved fabrics. T-shirts or short-sleeved shirts will not be enough. Permethrin-impregnated shirts and pants may be worth their weight in gold. And don’t forget to bring DEET repellent. Lots of it.