Identify caterpillars and, if possible, parasitoid (Sabah, north Borneo)

Question

Someone on Twitter posted some photos yesterday of a lump of mud that, when knocked off a chair by accident, revealed a number of caterpillars: https://twitter.com/solomilne/status/956135158381334528

I've uploaded one of the photos below. The assumption (which seems reasonable, but I suppose isn't certain) is that they were left there by a parasitoid.

Can anyone identify the caterpillars, confirm whether they are likely to have been left by a parasitoid and if so identify a likely culprit? The sample was from a forested area in Sabah, northern Borneo; I've requested a size from the person who posted the photos.

Answer 1

These are wasp larvae, but likely not parasitoids. They are the larvae of predatory Sphecid or Crabronid wasps, both of which build mud nests, generally provisioned with spiders or other arthropods that have been killed (and by some wasp species, dismembered) or paralyzed by the female (mother) wasp. It looks like one or two of them may be pupae (closer to eclosing--"hatching"--as adults) instead of larvae. If kept carefully they can be raised to adulthood for identification (at least by an expert familiar with the aculeate, or stinging, wasp fauna of that part of the world).