Those white things are wasp larvae eating this manduca caterpillar from the inside out.
Parasitic wasps lay their eggs in it. The eggs are coated with a virus that temporarily turns off the manduca’s immune system. When it’s immune system reboots, it is tricked into thinking that the eggs are part of the caterpillar. The eggs hatch, and they eat their way out and turn into pupae and the cycle repeats.
Anyone who has grown tomatoes before really appreciates the wasps. The hornworm caterpillar can devastate your tomatoes crop. It’s probably a terrible way to go for the caterpillar, but they are real pests.
The little bitty wasps that parasitize the oleander aphids on my milkweed are some of my best buddies.
The wasps are fine until you unwittingly jam a weed puller into their ground nest. They don’t like when you do that.