As the temperatures drop, things can seem a bit dead in winter - no buzzing bees, fluttering butterflies or sliding snails. There are many things we do as humans to survive the cold, but what about our invertebrate friends?
While most invertebrates don’t strictly hibernate, some will go into a state of ‘diapause’ - halting their development and spending the winter as either eggs, larvae, pupae, or adults, while some will slow down their metabolism in a state known as ‘torpor’.
Torpor lasts for a shorter time than hibernation and is caused by a change in environmental temperatures and availability of food, whereas hibernation is linked to hormonal changes and day length.
Here are just a few strategies from different invertebrate groups:
Moths and Butterflies
Moths and butterflies will survive at different life stages depending on their species. Meadow brown (Maniola jurtina) and small copper (Lycaena phlaeas) butterflies overwinter as caterpillars. Holly blue (Celastrina argiolus) and orange tip (Anthocharis cardamines) butterflies shelter as pupae, as do the hawk moth (Sphingidae sp.) family. Aptly named Winter moths (Operophtera brumata) and butterflies such as commas (Polygonia c-album), and peacocks (Aglais io) overwinter as adults, creating polyhydroxy alcohols in their blood which acts like an anti-freeze.
Painted ladies (Vanessa cardui) migrate and reached the news this summer as a once-in-a-decade mass migration to the UK from continental Europe and Africa was recorded.
This is an amazing journey for such a small butterfly but these butterflies journeying south are the successors of those who initially travelled north, so it is incredible that they don’t need to be shown the way!
Wasps and Bees
For social wasps, only the queen survives the winter. She may chew her way into hollow stems, or hide beneath a bit of bark, or under the eaves of roofs until it gets warmer again in the spring.
Similarly, queen bumblebees are the sole survivors over winter, foraging to build up energy before finding a safe place in loose soil or within dense vegetation to shelter.
Honeybees (Apis mellifera) stay in their hives, huddling around their queen to keep her warm and surviving on honey reserves. On warmer days, they may venture outside, but mostly wait until warmer weather in spring.
For the most part, solitary bees are short lived as adults, and lay eggs in underground tunnels or hollow stems before dying at the end of summer or autumn. The larvae emerge over winter and feed on reserves left by their mother.
Ivy bees (Colletes hederae) are active late into autumn and early winter feeding mainly on nectar from ivy flowers before laying their eggs underground.
Flies and Arachnids
Larger fly species shelter over winter as adults in trees, shrubs and grass tussocks. In people’s homes, they might find a quiet corner to hide until temperatures get warmer. Some flies overwinter as larvae underground or in bogs, and mosquitoes’ eggs survive in ponds amongst water plants.
Many of the smaller species remain active throughout winter. For example, winter gnats seem unphased by cold conditions and continue to fly, often in swarms, in the colder months.
Spiders cope well in winter; outdoor species will find a sheltered spot and become less active. Indoors, you might see more house spiders running around in autumn as they look for a mate, but not because they are looking for somewhere warm to hide. These species will be in homes all year round, and although they look big, they do no harm!
Harvestmen are related to spiders and most will similarly find a safe refuge to wait out the winter. This may be deep in long grass, amongst leaves, and some underground.
Snails and Slugs
Snails find somewhere quiet and sheltered and go into a state of torpor inside their shells creating a dried film of mucus like a door over the opening to keep the moisture in.
Many slugs will be active if temperatures are above 5°C but will also bury themselves underground or find refuge under logs. Some slugs such as the large black slug (Arion ater) can survive being partially frozen for short periods of time.
What can I do to help invertebrates survive the winter?
Unfortunately, with the climate breakdown affecting our winters, it’s becoming even harder for invertebrates to find enough food and survive the changing temperatures.
- Over-tidying of gardens and greenspaces can make it difficult for invertebrates to find shelter, so leaving dead flower heads, hollow stems, and ivy all provide excellent overwintering spots. You can also make simple shelters by tying a bundle of hollow stems together to leave somewhere undisturbed.
- If you find an invertebrate active in your home (most likely due to a temperature change) the best thing to do is to carefully move them to a cooler part of the house like a loft or garage, or to a sheltered space outdoors.
- Planting winter-flowering plants, such as snowdrops and hellebore, provides nectar for any brave pollinators venturing outside during milder days.
- Recording any invertebrates and wildlife you see in winter can help scientists understand the spread of different species. https://www.brc.ac.uk/irecord/