When it comes to surviving winter, insects in temperate regions like Montana can be divided into two groups: freeze-tolerant insects that can survive if their body fluids freeze, and freeze-avoiding ones that can't.
Certain flies, wasps, beetles and moth and butterfly larvae and pupae produce chemicals that control the rate and size of ice crystal formation in their bodies, so that freezing doesn't damage their cells. The pupae of one species of swallowtail butterfly has survived laboratory temperatures of -385 degrees F.
But insects in the second group must migrate to a warmer climate, or carefully select a site where they'll go dormant for winter. Some caterpillars and beetles find shelter under rocks and leaf litter, or burrow into soil, where deep, insulating snow can keep the temperature near freezing. The site must stay dry; frost or even dew touching the insect's body can freeze it.
Some mite eggs and worm pupae secrete wax around their bodies; many other insects build cocoons. And a wide variety of overwintering insects produce the cryoprotectant chemical glycerol, which lowers the freezing point of their body fluids.