Interesting. So will they kill the Saddleback when they hatch?

The host will likely die when the wasps emerge.

I originally thought the host WAS dead. I mean, how could you live if you had parasites on you? But that was my reasoning because I thought they were parasites. Seeing as they aren't parasites, but eggs, I suppose you are right and the caterpillar will live until the eggs hatch. And since they are wasp eggs, and the caterpillar is an easy meal, they will probably consume it. :). Fascinating!

Sorry for not explaining this a little better. The white objects attached are cocoons, not eggs (the eggs would be very small). The wasp larvae have already consumed the caterpillar from the inside, and have now spun their individual cocoons externally on the host. They will soon emerge as adult wasps. The host caterpillar may, indeed, already be dead as you mentioned, but it will almost certainly be dead by the time the wasps emerge.

No problem, Ross. You explained it fine. I just made a typo and said eggs rather than cocoons. Either way, they will be coming out of something (cocoon or egg). But that's really fascinating. I am always sad when insects die, but it is interesting when they are feeding another insect. Do you know if wasps are immune to the stings of saddlebacks? Because I am wondering how the larvae consumed it from the inside, if the stings are lethal to other bugs.

Adult parasitic wasps and flies are not immune to the venomous spines of these caterpillars, but they rarely encounter them because of their nimbleness and speed in depositing eggs on their bodies. The spines are mainly a deterrent to birds and other animals that would try to consume them.

Some studies suggest that these caterpillars are even more prone to being parasitized by flies and wasps than other species due to their more generalized feeding habits, which apparently makes them more "available".

The caterpillar venom is stored in glands at the base of the spines and does not circulate throughout the caterpillar's body. The growing wasp larvae, therefore, are not impacted, and are able to develop.

I got stung by these caterpillars on multiple occasions. Of course, it was unintentionally because they were on the underside of leaves. But seeing as our fingers are bigger than a parasitic wasp/fly, and due to your explanation, they can probably maneuver between the spines rather easily.

The studies are most likely correct and would make sense. These caterpillars are very slow compared to others that I have seen. I've found a specimen, and then gone to look for other insects for an hour or two, and then returned to find them not far from the location they were previously in. That would make them an easy meal for any insect small enough to attack it, before it can sting them.

So just so I can make sure I understand this:
1st: The wasp laid eggs on the host
2nd: The eggs hatched into larva
3rd: The larva ate through the outer layer of the caterpillar's skin, and made there way inside of it.
4th: The larva proceeded to eat from the inside until they were ready to make a cocoon.
5th: The larva crawled out and made there cocoons on the surface of the caterpillar.
Is that correct?

Members of the Microgastrinae can either deposit eggs externally on the host (ectoparasitic), or within the host (endoparasitic). We don't know what occurred in this particular case. I should have clarified that eggs can be deposited "on or within their bodies" in the previous paragraph.