How do monarch butterflies and other garden insects survive winter?
Butterflies, bees and other insects are small and fragile but they've evolved many strategies for coping with cold weather. Winter is relatively mild in New Zealand, so some insects are active all year round while others have different ways of coping with unpredictable weather. During their life cycle, insects go through four stages: egg, larva, pupa and adult. By timing their life cycle to annual weather conditions, the population can survive the winter even if individual insects die. Here are five overwintering strategies.
1. Take a break
Diapause occurs when development is interrupted or suspended until conditions are right. Depending on the species it can occur at any stage of the life cycle. Monarch butterflies go into diapause at the end of summer. The adult butterflies that hatch in late autumn are sexually mature but won't breed until spring. A monarch might live for six to eight weeks after it has finished reproducing during the summer, but the winter generation of monarchs may live up to nine months.
You may be lucky enough to see a big cluster of monarchs in a sunny spot on a large tree. Overwintering sites for migrating monarchs in Mexico and the United States are well known. Much smaller overwintering sites occur here too. Jacqui Knight from the Monarch Butterfly NZ Trust says there are known sites up and down the country, as far south as Oamaru. The Trust is tagging monarchs to learn more about how they overwinter. The tags are small and very light so do not hurt the butterfly or affect its ability to fly. If you'd like to find out more and join the tagging project register at monarch.org.nz.
2. Lay eggs
Passionvine hopper adults all die before winter but they leave behind hundreds of eggs laid in lines along thin twigs. The eggs hatch in spring ready to take advantage of the sap flowing in new plant growth.
3. Make the most of winter conditions
Some insects do most damage in winter. Grass grubs and porina moth caterpillars burrow into soil softened by rain and munch away at grass roots and leaves.
4. Hide inside
The larva of lemon tree borer tunnel into the branches of citrus and many other trees and shrubs. There they live for up to a year, protected from predators and the weather before emerging as flying adults in spring and early summer. Tree weta live in tunnels in wood too. You may find some in your firewood pile.
5. Stick together and plan ahead
Honey bees store honey in summer to keep the colony alive in winter. Worker bees keep the hive warm by raising their body temperature by vibrating their wing muscles – but they need energy from honey to do so.
- NZ Gardener