I love the spring. The weather warms and the snow melts. A fun time to get out in the woods with my dog, Ole. This time of year is great, until the week before Memorial Day. What happens during that week? The mosquitoes come out and they usually come out in a big way. A wave of annoyance that drives both man and dog crazy. If you haven’t already figured it out, let’s talk about mosquitoes and their place in the Northwoods.
Northern Wisconsin’s abundant lakes, wetlands, and forests, provide ideal habitat for a diverse array of mosquito species. More than 50 species and multiple genera of mosquitoes have been identified in Wisconsin. Among the most frequently encountered in the Northwoods are the inland floodwater mosquito, Aedes vexans, known for its widespread presence and prolific breeding after rains. Other common woodland species include Aedes communis and Aedes canadensis, which are early-season biters. The Northern House Mosquito, is also prevalent, often found breeding in artificial containers and stagnant water around our homes.
The mosquito life cycle is a fascinating with a rapid four-stage process: egg, larva, pupa, and adult. Female mosquitoes lay their eggs on or near water. For many floodwater species like Aedes vexans, eggs are laid in low-lying areas that are prone to flooding. These eggs are incredibly resilient and can lie dormant for extended periods, even years, waiting for the right conditions. Once these eggs are submerged in water, they hatch into larvae, often called "wrigglers." The larvae are aquatic and feed on algae, protozoa, and other organic matter in the water. After about a week to ten days, depending on temperature and species, the larvae transform into pupae, known as "tumblers." The pupal stage is a non-feeding, transitional phase where the mosquito undergoes metamorphosis. Within a few days, the adult mosquito emerges from the pupal casing, ready to fly and, for females, seek a blood meal necessary for egg development. Male mosquitoes, in contrast, feed solely on nectar.
The phenomenon of a "big wave" of mosquitoes in late May in northern Wisconsin is primarily due to the synchronized hatching of floodwater mosquito eggs. As the snow melts and spring rains arrive, they saturate the dormant eggs laid in previous seasons in floodplains and temporary pools. The warmer temperatures around late May trigger a mass hatch, leading to a sudden surge in adult mosquito populations. These species have evolved to develop quickly, often taking less than a week from egg to adult once water is present, allowing them to take advantage of transient water sources.
While the late May explosion marks the peak emergence of many species, you might encounter a few mosquitoes earlier in the spring. This is because not all mosquito species overwinter in the same life stage. Some species, like the Winter Marsh mosquito, can overwinter as adult females. These hardy females find sheltered locations, such as hollow logs, culverts, basements, or even caves, where they enter a state of diapause, a kind of insect hibernation. They slow their metabolism and can survive freezing temperatures by replacing some of their body water with glycerol, acting as a natural antifreeze. As soon as temperatures consistently rise above freezing in early spring, these overwintering adults become active, often emerging to seek a blood meal and lay their first batch of eggs, contributing to the initial, smaller mosquito presence before the main floodwater mosquito hatch.
Despite their reputation as annoying pests and vectors of disease, mosquitoes play a crucial role in the food web. In their larval stage, they are a significant food source for many aquatic organisms, including fish, amphibians like frogs and salamanders, turtles, and predatory aquatic insects such as dragonfly nymphs. The sheer biomass of mosquito larvae in wetland ecosystems makes them a vital link in the aquatic food chain. As adults, mosquitoes serve as prey for a variety of animals, including birds, bats, spiders, and other insects like dragonflies and damselflies. Since, male mosquitoes feed on nectar, they act as pollinators for various plants. While they may not be the primary pollinators for many agricultural crops, they contribute to the reproduction of numerous wild plant species, including some orchids.
Mosquitoes are annoying. We may wish for their absence during outdoor activities, but mosquitoes are an integral part of the natural balance in northern Wisconsin's ecosystems.
