WITH WINTER DOING ITS WORST THIS YEAR, many of us are seeing a lot of birds and squirrels at the feeders. But other animals we see frequently in summer, such as chipmunks and most insects, are nowhere to be found. Here’s a little overview of where some of your gardening friends are spending the winter, starting with insects and spiders.
Animals that are not warm-blooded, as mammals are, have difficulty generating enough heat to use their muscles in cold weather. With cold, their muscles stop responding and they just slow down until they finally can't move any more. This is why you'll sometimes find a "sleeping" bee on a flower in the early morning: The over-eager bee got caught by dropping temperatures and became dormant before it could get home. Usually the bee will "wake up" as soon as it warms up.
Insects and spiders and other animals that are referred to as cold-blooded (though what is circulating in their bodies is not, technically, blood), typically either die with the first frost or spend cold days "asleep"--that is, in a state more properly referred to as dormancy. They are very vulnerable during dormancy, and are a lot safer if they have a sheltered spot in which to hide.
Some butterflies migrate to warmer climates. (Monarchs are famous for this.) But many dormant butterflies are present in and around your garden all winter. Depending on species, they may overwinter as caterpillars, in the chrysalis (the enclosure in which they transform from caterpillars into adults), or as adults. Woodpiles, brushpiles, untended flower beds, and trees with loose bark are all popular spots for overwintering butterflies.
Most bumblebees die when cold weather arrives. However, the pregnant queens survive, spending winters in abandoned mouse nests or other holes in the ground, waiting for warm weather to lay their eggs and raise a new crop of worker bees. Because of their “furry” coats and ability to generate heat by shivering, bumbles are able to move around even during fairly cold weather. (They even are found in the Arctic tundra, where they pollinate the small patches of wildflowers that grow on the carcasses of dead animals.) This is why bumblebees are often the first insects you’ll see in spring. It's also why that bee you find sleeping on a flower in the morning is probably a bumble; they're the ones most likely to still be out even when temperatures are dropping.
Dormant spiders are often found in leaf litter, where they wake up and move around on warmer days. These spiders are an important source of winter food for birds, which is why you’ll see small birds poking around in the leaf litter in your garden if you were kind enough to leave it there for them. Contrary to a widespread misconception, outdoor spiders rarely enter homes in search of heat; spiders that are adapted to life outdoors probably can’t survive indoors, as the indoor air will be too dry for them. Spiders found living inside homes are usually nonnative spiders that are adapted to living in dry, warm climates. If you take them outside, they will probably die.
Many insects experience not only dormancy but also diapause. Unlike dormancy, which is a physiological reaction to dropping temperature, diapause is a genetically programmed response that often triggered by changes in the length of the day. In diapause, the animal doesn’t just stop moving but also stops developing; this is nature’s way of ensuring that it will be at the proper stage of development (e.g., emerging from the chrysalis) at the right time of the year (e.g., when flowers are in bloom).