A sign that Fall is settling in is when there are many sightings of black & rusty orange caterpillars criss-crossing the roads and open lawn spaces. We often call them “wooly bear caterpillars” though they’re actually called the Isabella Tiger Moth larva and are scientifically known as Pyrrharctia isabella. The first part of its name, “pyr” refers to ‘fire’ for its fuzzy orange bands and the last part “arctia” indicates that this caterpillar can be found in Arctic regions, sometimes found frozen in ice. They’re one of the few arthropods that can tolerate sub-zero temperatures using cryoprotectants in their body to prevent organ tissue damage. Once these larvae thaw out in the Spring, they’ll be crawling around for about two to four weeks before they pupate, develop a cocoon and then hatch as a moth. This process can take longer in the Arctic regions, sometimes spanning up to 14 years. The caterpillars are used as a food source for birds, parasitic wasps and skunks. Also being munched on by bats, birds and spiders during their adult moth stage. This species relies on maple, elm and birch trees as host plants but also feeds on grasses, dandelions, wild plantain and clovers that may be growing in your lawn. They lay eggs twice per year while going through two generations each year. The adult moths are a mid-sized cream-colored moth with a series of black dots down its yellowish abdomen. Adults are only fluttering at night for one to two weeks within wooded areas, crop fields and grassy roadside areas.
There’s been a myth surrounding the Wooly Bear caterpillars that by looking at the caterpillar’s orange and black bands they’ll tell us how severe the upcoming winter season will be. If you see more black bands then winter may be somewhat harsh while having more snow. However if there’s more orange bands, then winter will be mild. Who knew a caterpillar has the power to predict seasons. But is it true? Unfortunately there isn’t enough evidence to support that the caterpillars can predict the winter seasons for us. This story began during the early colonization across North America when many caterpillars were spotted during the construction of roadways during the Fall season. Back in 1948, Canadian researcher Dr. Charles Howard Curran, who was a curator at American Museum of Natural History in New York City gathered a team of fellow colleagues, along with his wife, and went on a trip upstate to collect a handful of caterpillars to determine if they could actually prove whether this folklore was in fact true. However with only 15 caterpillars collected, it wasn’t enough data to make a scientific consensus. Dr. Curran has a local connection. He was born in Orillia in 1894, became an entomologist during the mid 1920s following his service as a machine gunner in WWI from 1916 until he was wounded in 1918. What he and his team were witnessing was actually the different stages in molts. The Isabella Tiger Moth caterpillars will molt six times while each molt will shed more black bands starting in the middle of its body revealing more orange bands and leaving black bands on its head and rear end. There are thirteen bands total and when molting is complete the caterpillar may become fully orange or rusty orange in colour.
For now, we’ll have to stick with modern day technology and the expertise of meteorologists to help us determine what is changing in our weather patterns. Most of the caterpillars spotted this season are matching each other so it’s certainly difficult to tell. Either way, winter is on its way and it’s best we tolerate it however we choose through fun winter activities such as snowshoeing, skiing or snowmobiling.
Matt Thomson is a local conservationist based in Severn and enjoys engaging the community through citizen science events & activities. Be sure to follow him on Instagram or Facebook, @ardtreanature.
