One species in particular, the Arctic woolly bear is unique for being an incredible survivor because it has to contend with some of the harshest conditions on the planet. In many ways though, there is not much difference between what they do and what other caterpillars do. When the eggs hatch, the larvae feed constantly just like any other caterpillar. But this one needs to spend a long time feeding due to the climate in which it lives.
The Arctic woolly bear moth’s range extends to the Arctic Circle, in Canada and even Greenland. In such conditions, a caterpillar has to overwinter in its larval form. This far north, the shortages in vegetation mean that food does not come easily and so the woolly bear has to spend a long time frozen. While covered in ice and frost, the little creatures must depend on a cryoprotectant, or antifreeze in order to stay alive. These cryoprotectants are based on sugars in their bodies, which in turn protect their delicate tissues from temperatures that ordinarily plummet below zero. Some have been found surviving through temperatures 70 degrees below freezing.
Many cold-blooded animals have an antifreeze chemical or chemicals in their blood. For example many fish and frogs that live in colder climates will also allow themselves to be frozen. Once thawed out they will resume activity once more. The Arctic woolly bear moth caterpillars are no different.
They do take their adaptations a few steps further though. They may live through as much as seven winters in harsher climates. Here, the summers are so short and their food demand is so high that even a full day spent eating is not enough to sate the larva’s immense appetite. Only 5% of their lives are spent eating their favorite food, the tiny Arctic willow.
The larvae even use a special type of cocoon called a hibernacula to shield themselves. These cocoons also help to protect the caterpillars from parasitoids, although some parasitic ichneumon wasps and flies still manage get their victims. More than 90% of their life is spent in the hibernacula, while much of the feeding occurs in June. Come spring though, wherever they live, some woolly bears will become adult moths.
The Arctic woolly bear moth is not the most conspicuous or even the most well-known of all lepidopterans. It is certainly not the most attractive insect, coming in shades of grey with rather complex black patterns. The upper wings are much darker than the under wings. As adults, the moths have just a few days to find a mate and reproduce, after which they die. They lack mouthparts and are unable to feed, just like many other species of moth. So you wouldn’t find this moth pollinating any flowers or drinking nectar any day soon.
The moth’s life though is far from sorrowful. The imago, or adult form, has only one purpose and that is to mate and reproduce, leaving another generation of caterpillars to survive through the winter as little insectoid popsicles buried under frozen soil.
Photos by Kristy Doyle. Check out her blog, north of sixty.