Caterpillar identification can be difficult and it is often easier to rear caterpillars that you find and identify the adult moth.
Rearing moths is great fun and is relatively straight forward. Key points are:
- Food. Some caterpillars are very fussy so providing the correct food-plant is essential. It is best to use stems or leaves from the plant on which the caterpillar was found. A regular supply of fresh food will be required.
- Container. A ventilated plastic container can be used (such as a margarine tub for smaller caterpillars or an ice cream tub for larger ones). A sheet of kitchen towel in the bottom of the container will make cleaning easier and will absorb excess condensation.
- Hygiene. Frass (caterpillar droppings) and old/dead leaves should be cleared out of the container regularly to avoid the growth of mould.
- Temperature. Caterpillars can be kept indoors, ideally in an unheated room and should not be left in direct sunlight.
Remember some caterpillars have irritating hairs so it is best not to touch them.
When fully grown the caterpillar will undergo pupation. Many moths pupate underground so you can provide a layer of compost in the container; others will spin together the leaves of their food-plants to form a cocoon. A few, such as the Puss moth and Sallow Kitten need a nice piece of bark on which to build their cocoon.
Pupae that form during the spring or summer usually hatch within a few weeks. Pupae that form in autumn will overwinter and should be kept in their containers in a cool but frost free place (e.g. an unheated shed or out-house). The soil/pupae should be lightly misted with water very occasionally over winter and spring to keep the atmosphere humid.
When the adults are ready to emerge, a few twigs should be placed in the container to enables the moths to climb up and inflate their wings. You should ensure that the container is large enough for the moth to expand its wings.
The emerged moths should be released back in the same area as the caterpillars were found. If the caterpillars you have reared are from an entomological supplier or are exotic species, you should not release these in to the wild. Indeed, it may be illegal to do so.