The winter solstice—the shortest day of the year and the official start of winter—has come and gone, and the days are now getting longer.
In this cold, dormant time, it might come as a surprise to learn that insects survive the winter. They have various strategies to do this. Many species go through diapause, a delay in development in response to adverse environmental conditions. The eastern population of the Monarch (Danaus plexippus) butterfly migrated last fall to overwintering sites in the Oyamel Fir (Abies religiosa) forests of Mexico. They usually arrive there around the Día de las Muertos, which is celebrated November 1 and 2. They rest there and won’t feed on milkweed until temperatures are warmer. Then they begin to migrate back north. And the reason you can find the Mourning Cloak (Nymphalis antiopa) butterfly flying around so early in the spring (often in March in Connecticut!) is because in winter they hibernate as adults in tree holes and other crevices.
Many lady bugs, or ladybird beetles (family Coccinellidae), will overwinter as adults, piling on one another in big groups inside hollow logs and under rocks. This helps them stay hydrated and avoid predators. Last fall you might have noticed their large gatherings around your dark shutters and white-framed windows. Usually this is an introduced species, the Asian Lady Beetle (Harmonia axyridis). These beetles will sometimes crawl into a home through cracks. When disturbed, they emit an acrid odor and can stain surfaces with a yellow secretion.
If you see a moth flying at night in December in Connecticut, it is likely the male Winter Moth (Operophtera brumata). This invasive species, introduced from Europe, can defoliate oak and maple trees as a caterpillar (larva). The larvae burrow into the ground to pupate and the adults emerge in late fall and early winter. In cold temperatures male moths rapidly vibrate their flight muscles to warm themselves and then fly off to seek out females. Females don’t fly, but crawl up a tree and emit a pheromone to attract males.
Some insects overwinter as larvae. The Wooly Bear caterpillar, the larva of the Isabella Tiger Moth (Pyrrharctia isabella), are seen traveling across roads and paths in the fall. They are now dormant under the heavy cover of leaf litter. These caterpillars produce glycerol, an antifreeze, which keeps their cells from freezing.
Insect species that spend the winter as an egg include praying mantids. Before she dies in the fall, an adult female mantid will lay an inch-long (2.54 centimeters) frothy sac, which hardens into a protective egg case, or ootheca. I once made the mistake of bringing an egg case indoors one fall and that winter 100 young hatched!
We might not be thinking of insects and other invertebrates as active now. But many of them are. Beneath the ice of ponds and streams the immature stages of stoneflies (order Plecoptera), caddisflies (order Trichoptera), mayflies (order Ephemeroptera), and dragonflies (order Odonata) are actively feeding on smaller aquatic invertebrates or plant material, depending on the species. These insects are growing and adding body mass so they can emerge as fully flighted adults in the spring. Dragonfly nymphs, like the adults, are carnivorous, feeding on other invertebrates and even tadpoles and salamander larvae. Some spend a few years as a nymph before maturing into an adult.
The larvae of caddisflies are found in a wide variety of aquatic habitats, including streams, rivers, lakes, ponds, and vernal pools. Many species of caddisfly larvae use silk to make protective outer cases with gravel, sand, twigs, bitten-off pieces of plants, or other debris. The larvae feed in different ways depending on the species. Some are predators, some shred leaves, others graze on algae or collect particles from the water column or on the bottom.
We don’t often think about insects during the winter, or just believe that most have died. If we do see one, we think it is an anomaly or accident of nature. In fact, many insects are still living with us, either dormant or active, during the winter months.