A couple of weeks ago I talked about the near-record-breaking April rainfall we had in southeast Michigan, and the flooding that followed. Since then the floodwater has been receding, leaving behind many ephemeral pools in the local floodplain forests:
These temporary bodies of standing water provide ideal habitats not only for frogs, toads, and salamanders, but also mosquito larvae (family Culicidae). As I crouched at the edge of the pool above, I could see the surface rippling with innumerable larvae (this is why they’re called “wigglers”). These young mosquitoes complete their development entirely within standing water. Any still water will do, even if it’s polluted and devoid of oxygen. That’s because the larvae breathe atmospheric oxygen at the surface of the water. Most feed on aquatic microorganisms that fuel their growth and development, although some species prey on other mosquito larvae. As holometabolous insects, the larvae eventually pupate and then emerge as mature adults. And that’s when the trouble starts for people.
These small, delicate adult flies feed on plant nectar and juices for their own nutrition. The females of many species, however, lack the amino acids necessary for egg development. They obtain these nutrients from the blood of vertebrates. After engaging in mating swarms to have their eggs fertilized, females seek out blood meals. They buzz around somewhat randomly until they detect the carbon dioxide that vertebrates exhale, and then follow it to the source. Females pierce animal skin with their proboscises, inject anti-coagulants, and draw the blood. Their digestive systems then break down the blood proteins into the amino acids their eggs require to develop.
A single mosquito bite seems like little more than a mildly painful nuisance. In this particular floodplain, however, the mosquito population will soon reach plague-like proportions. In the summer I’ve been swarmed by hundreds of them, with only a thin barrier of DEET preventing me from being mauled. They still go for my eyes, nostrils, and ears, however, and sometimes they even overcome the chemical repellents. Mosquitoes are the single biggest deterrent to me entering floodplain forests in the summer.
On top of this general nuisance, mosquitoes are vectors of several serious diseases. In warmer climates malaria, yellow fever, and other conditions are life-threatening and often fatal. Malaria alone kills almost one million people annually. While we don’t have that problem here in Michigan, we do have to contend with various forms of encephalitis, meningitis, and West Nile virus.