Female moths lay between 100 and several thousand eggs, depending on species. If all these matured and laid more eggs, then after several years the world would be covered in caterpillars.

Their parasites stop caterpillars in nature from taking over the world. The main parasites of caterpillars are particular species of mites, wasps and flies.

Cryptoptila immersana caterpillar carrying green mites.

The exact relationship of the various species of Lepidoptera with the various species of mites (Acarina), flies (Diptera), and wasps (Hymenoptera) is often very specific, and of great importance in pest control. If you should get some flies and/or wasps emerge from your caterpillar or pupa, you might consider donating them to your local natural history museum or university entomology department, who may have study programs on these parasites.

two Tachinid fly larvae recently emerged from a moth chrysalis,
one grub having already pupated.
(Photo: courtesy of Peter Street, Gosford)

The flies attacking caterpillars come mainly from the family TACHINIDAE.

dying Manulea replana, caterpillar with cocoons of a number of wasp parasites.

Wasps that attack caterpillars come from a variety of families, including: