An Excerpt from Jim Conrad's
Naturalist Newsletter

from the September 26, 2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO

Here during the peak of the rainy season nearly every afternoon it rains. If a bucket or tin can stands upright it stays full of water, and if you get down close enough to the water's surface inside these buckets and tin cans, you'll see what's shown below:

mosquito larva and pupa -- WIGGLETAILS & TUMBLERS

As a kid back on the farm in Kentucky I spent a lot of time with my head hung over the rim of a large, wooden barrel bought cheaply from nearby Glenmore Distillery (Kentucky Tavern Bourbon). The barrel caught rainwater off the coal-house roof, for the washing of our clothes. During my whole childhood the barrel smelled agreeably of aging whisky, but I didn't stick my head over the barrel's rim for the odor. I was watching a seething metropolis of aquatic critters, among the most common and fascinating of which were the ones in the above picture.

My father told me that the larger white things in the barrel, like the one at the left in the picture, were "wiggletails," and that they developed into mosquitoes. They were called wiggletails because they swam through water by violently jerking their bodies back and forth, "wiggling their tails." Later in school I also learned that if we wanted to cut down on the mosquito population around our house the first thing we needed to do was to go around emptying all open containers holding water where mosquitoes could lay their eggs, for those eggs would hatch into wiggletails, from which later mosquitoes would emerge.

But, there was something missing in the above story, and the error didn't occur to me until I'd asked insect-identifier Bea in Ontario if she know what that dark, comma-shaped critter was to the right of the wiggletail in the picture. She shot back that it was a mosquito PUPA!

Of course. The thing wrong with the whisky-barrel story was that mosquitoes belong to the insect order Diptera, along with flies, and dipterids undergo complete metamorphosis, entailing these four stages:

egg --> larva --> pupa --> adult

Our egg --> wiggletail larva --> adult mosquito story accommodated only three stages. Bea's comma-shaped pupa supplied the missing link.

Over 2500 different species of mosquitoes are known throughout the world, and some 150 of those occur in the US. Therefore, there are many variations on the mosquito theme. However, what follows applies to most species.

Wiggletails, or mosquito larvae, frequently must rise to the water's surface where they poke their rear ends upwards and breathe air through a siphon tube, which is exactly what the one in the picture is doing. Happily, Anopheles larvae -- the adults of which convey malaria -- bear no siphon and must float parallel to the water's surface for air. Therefore, the wiggletail in the picture isn't a malaria-carrying Anopheles. Wiggletails feed on microorganisms and organic matter in the water. As they grow, they shed their skins four times. Usually they live in water between one and two weeks, depending on the temperature -- the hotter it is, the faster they develop.

The brown, comma-shaped pupas, sometimes referred to as "tumblers," don't feed. Even though as they move through water they jerk about as violently as the larval stage, in the mosquito's life cycle they constitute the "resting stage." After about two days of existence pupas rise to the water's surface, their pupal skin splits and the adult mosquito emerges from the pupa's old skin onto the water's surface. The newly emerged adult rests on the surface awhile as it dries, its parts harden, and its wings spread out and dry so it can fly away.