A bonus of the sometimes brutal Midwest winters is the absence of creepy crawlies that take a bite out us during the summer months.
But in forest preserves that ring the city and suburbs and along the banks of outlying creeks and ponds, a small group of bugs not only survive the deep freeze, they thrive. Mother Nature has given them a vital secret weapon to deal with the harsh Midwest cold: a unique protein or fluid that chemically acts just like antifreeze, preventing them from freezing to death, experts say. Finding mates is a breeze and food is plentiful; once they gobble up the dead leaves and plant matter they enjoy, the digested matter enriches the soil around them, local entomologists say.
"They really help to break down a lot of the plant matter that gets (into) the stream in the fall," R. Edward DeWalt, an aquatic entomologist with the Illinois Natural History Survey explained. "(If) you didn't have insects and some invertebrates doing that, you'd just have rivers jammed full of leaves and sticks all the time. Because you have large numbers of insects in the stream, you can take these mass of leaves and they're pretty much gone by March or April."
This winter, temperatures have been average -- save for this month, when temperatures have been about 8 degrees cooler in the Chicago area, according to the National Weather Service. Snowfall this winter had been below average until the recent snow totals put the Chicago area above average, said Ben Deubelbeiss, a weather service meteorologist.
But DeWalt warned that climate change could alter everything from the times when they emerge to their migration patterns. Changing weather patterns in the southern U.S. had already led to fewer winter stoneflies -- an aquatic insect also abundant in the Chicago area -- hatching there, with them emerging from November to January instead of March, he said.
"This is what we have to look forward to, perhaps by the end of the century," DeWalt said. "Illinois winter temps have already increased. So far, no range changes noted, but my prediction is that some (stonefly) species will migrate further northward while others will be removed from the southern part of the state."
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Illinois is home to at least 50 different species of insects, arachnids and organisms that emerge during the winter months to either feed or lay eggs before the spring thaw.
One of the most abundant of the local winter insects are the winter stoneflies, aquatic insects that emerge as adults from oxygen-rich freshwater typically outside of the Chicago area beginning in November. In fact, 20 species of the state's 65 native stoneflies emerge during November through March, according to the Prairie Research Institute. Stoneflies can be found in wooded areas from the Kankakee down to the Vermillion rivers, climbing trees to eat algae and fungus to nourish their eggs and help them mature. They mate and lay eggs back into the stream. The eggs hatch quickly and the stonefly nymphs will stay in the water through the summer until they emerge as adults in November to restart the life cycle.
Many of these insects require very specific conditions to survive, experts say. The winter stonefly, for example, prefers life beyond the city, said Crystal Maier, the collection manager of insects at the Field Museum.
"They are restricted to very clean water," she said. "They need water that's fast-flowing, it has to be super clean, free from pollutants, and they will only survive in those clean streams. It's not that Lake Michigan isn't clean -- can't comment on that -- it's that it's the wrong type of habitat."