Zombie caterpillars

Nature has some bizarre corners. A couple of years ago, I saw these caterpillars, part of a large group steadily demolishing a small shrub.

[Warning: from here on in, this blog is just plain wrong!! I now know that these are yellow-necked caterpillars, Datania ministra, the white hairs are normal, and this strange U-shaped posture is their defensive posture. There is no zombie fungus involved!. I’m leaving it up as a warning not to believe everything I say! MY, September 2019]

Then this year I saw this group, all together on a branch a few feet off the ground, each one bent into a U-shape, not eating, and not moving, though they were alive (I poked them gently).

I thought they were the same kind and were about to pupate, but I was wrong, on both counts. I hadn’t noticed the tiny white hairs on some of them, and the next day, they looked like this:

In close up, you can clearly see the “hairs” are growing out of their bodies:

This is a fungus which penetrates their bodies, and then absorbs nutrients from their insides, leaving a shell. This next photo is of a different group of caterpillars on the same tree. You can see that the segments  of caterpillar between each pair of legs are getting hollowed out as the fungus does its work:

A thunderstorm destroyed the whole ghoulish tangle, so I will never know what the final stage would have looked like.

By the way, I have failed to identify the fungus or the caterpillar, but the fungus is probably a type of Cordyceps. If anyone knows, let me know.

PS: I did wonder if it was not a fungus but some sort of communal cocoon, but my friendly mushroom expert confirmed the fungal guess. And if it was a cocoon,  it would need to survive a thunderstorm.