Bug o’the Week – Floodwater Mosquito –an homage

Howdy, BugFans,

Homage: “something that someone does or says in order to show respect or admiration.” (Macmillan).  In this case, it’s a grudging tip of the hat – we may not appreciate them, but we acknowledge that they are very good indeed at what they do.

The BugLady struck a deal with mosquitoes a very long time ago – she doesn’t bite them and they don’t bite her (alternatively, as one of her offspring suggested, she may just be tough and sour).  The only species that didn’t sign off on the pact, and the only species that raises a welt on her, is what she’s always called the “August mosquitoes” – the small, aggressive floodwater mosquitoes that seem to be biting with one end before they’ve fully touched down with the other.

There’s been a lot of rain in the BugLady’s corner of Wisconsin lately (including a localized 7” deluge that drowned the BugLady’s car in its parking lot, a story for another day).  Ample rain in the weeks before that had given the floodwater mosquitoes a start.  The BugLady will be trying to squeeze in a lot of trail time now, in an attempt to beat the inevitable population explosion.

Floodwater mosquitoes made the news here in 2018, when a dry July was followed by massive rainfall in August, which was followed by a massive mosquito hatch that made September miserable.  School groups that traveled to the local Nature Center for outdoor experiences were begging to go inside after only 15 minutes outside.

With some insects, you look at the common or the scientific name and wonder about the story behind it.  Not so with the floodwater mosquito/inland floodwater/freshwater mosquito.  The common names are pretty straightforward; the scientific name Aedes vexans comes from the Greek aedes, meaning odious or unpleasant and the Latin vexare, meaning “to annoy, torment, or harass.”  A century ago, it was called Culex sylvestris, the swamp mosquito.

They’re found in damp areas on five continents (they haven’t discovered or been inadvertently carried to Hawaii, Antarctica or South America yet), and they’re less common in far southern, far northern, and high-altitude North America.  Their needs are simple – food, in the form of nectar (him) and the blood of a large mammal (her), shelter, and a suitable place to deposit her eggs.

Males https://bugguide.net/node/view/1340555/bgimage, of course, are strict vegetarians, feeding on nectar and honeydew.  Females also consume carbs, but she needs protein from a blood meal in order to form eggs https://bugguide.net/node/view/11025/bgimage.  Larvae https://bugguide.net/node/view/1751200/bgimage eat bacteria and other tiny goodies they find in the water and on underwater surfaces.  For a Mosquitoes 101 review, see https://uwm.edu/field-station/the-mighty-mosquito/.

Their egg-laying protocol, which is typical of the genus, calls for the female to gamble.  She lays around 150 eggs, placing them on the ground, one at a time, near water at damp, grassy edges and in roadside ditches and depressions – spots that are destined to get wet – rather than directly into standing water like most mosquitoes.  She makes her choice based on her read of the existing soil moisture and on the presence of enough leaf litter to keep the soil damp until it floods.  When these areas become pools after a rain, her eggs can hatch into aquatic larvae within a week and emerge as adults in another week, especially in warm temperatures.  There are multiple generations per year, and they are with us throughout the mosquito season – one exterminator says that at any given moment, 40% to 50% of mosquitoes on the wing are floodwater mosquitoes.  The final generation overwinters as eggs, ready to get down to business the following spring.  Adults live for three to six weeks.

And if it doesn’t rain?  No worries – her eggs can dry out and wait for years for the right conditions to come along and rehydrate them.

Unlike other mosquitoes, floodwater mosquitoes are no stay-at-homes, traveling ten miles and more from breeding sites.  They are certainly tenacious – one sat on the BugLady’s wrist as she changed camera lenses so she could take its picture – denim does not faze them, and, they’re hard to photograph because most of them head directly for the ears, face, and neck.

When it comes to the floodwater mosquito’s epidemiological reputation, the reviews are mixed.  Aedes is a largely tropical/subtropical genus that contains some notorious disease-spreaders.  One source was relieved that, since there are so darn many of them, floodwater mosquitoes don’t carry diseases (on this continent).  Other sources say that they have the genetic potential for carrying several kinds of encephalitis, Zika, and West Nile Virus (and have transmitted them under laboratory conditions), but they are not a factor in transmission in the field.  Still others say that they do spread these diseases, plus dog heartworm, but they are “secondary vectors” – that is, other mosquito species, notably Culex species, do the heavy lifting and the floodwater mosquito simply dabbles.

Who would have guessed that laying eggs on land would be a successful strategy for mosquitoes!

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/