Grubs came out of my caterpillar, what is going on?
Anthela acuta caterpillar with red parasites.
Female moths lay between a hundred and several thousand eggs, depending on species. If all these matured into adult moths, and these laid more eggs, etc, then after about four years, all the world land masses would be about a metre deep in caterpillars.
In nature: the parasites, parasitoids, and predators of caterpillars stop them from taking over the world.
Note that 'parasitoids' are parasitic and actually kill their host, whereas 'parasites' just feed off their host but leave it alive.
The main parasitoids of caterpillars are particular species of viruses, bacteria, fungi, mites, ticks, wasps and flies.
Caterpillars are just as susceptible to disease as we are, and get the equivalents of flu and measles etc. The viruses in the Cypovirus genus, and the bacterium Bacillus thuringiensis are especially fond of attacking caterpillars, and are used as a biological control agents against pest caterpillars.
The exact relationship of the various species of Lepidoptera with the various parasitic species of mites (Acarina), flies (Diptera), and wasps (Hymenoptera) is often very specific, and is also of great importance in pest control.
If 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. In due course, there will be study programs on what particular parasites attack what particular species, to understand our ecological systems.
The flies attacking caterpillars come mainly from the family TACHINIDAE.
Wasps that attack caterpillars come from a variety of families, including:
When a caterpillar is infected with a parasite or parasitoid, its behaviour changes, just as ours does when we get a cold or a fever. So though normally caterpillars will keep hidden, caterpillars when infected sometimes start wandering aimlessly about. So if you find a caterpillar wandering about, it is probably ill already.
Predators also control the caterpillar populations,
such as spiders:
and adult wasps which catch caterpillars, paralyse them, and lay eggs on them, so that when the wasp eggs hatch: the wasp larvae have a ready fresh food supply.
and various Bugs attack caterpillars, like Shield Bugs (PENTATOMIDAE)
and Assassin Bugs (REDUVIIDAE)
and Scorpion Flies (MECOPTERA : BITTACIDAE) :
and of course Praying Mantids (MANTODEA) will happily feed on any life stage of any Lepidoptera:
and so will birds:
Even plants attack Lepidoptera:
(updated 3 February 2013, 3 December 2018, 9 December 2019, 10 September 2020, 19 April 2021)