Typically they're waiting for ideal environmental conditions.

Insects are ectothermic (cold blooded) so they can only operate when its warm outside, and many species use diapause to hibernate safely through the winter. Insects will go into diapause in their eggs or pupae (cocoons) which are much more resilient than their adult bodies, and build their pupae in safe, warm places like underground, deep in trees, or under decaying leaf matter where it doesn't go below freezing during the winter, emerging from their pupae when it gets warm enough.

Many insects also struggle to manage dehydration as adults, so they'll go into diapause during dry seasons and emerge as adults in the wet seasons.