Caterpillars munch on a wide variety of plants:
Caterpillars spend the winter tucked into a bark crevice. The following summer they spin a cocoon from silk, become a chrysalis and emerge as an adult the following summer.
There is even more about this species on the main Butterfly Conservation website
Caterpillars of the Swallow-tailed Moth look just like twigs. They spend the day completely still, feeding only at night, to avoid being detected by predators.