Especially in the case of A. atropos, the immense amount of food plant, which is devoured until pupation, could also be decisive for the individually laid eggs. They are also site-loyal, so in my opinion the single egg-laying makes total sense.
I have also noticed cannibalistic behaviour in Smerinthus ocellata. Similar to what you have described, Mothdragon, the victims are mostly caterpillars that are resting before moulting. Whereby I assume that atropos has the clear intention of wanting to eat. In the case of ocellata, there could be a risk of confusion: I have observed that the anal horn is nibbled and the caterpillar usually survives. But a caterpillar in moulting rest of ocellata is also more able to defend itself than in atropos. They lash out very fast and hard.
I would be interested in your thoughts on this. Intentional or accidental? Or an attempt to eliminate a food competitor? After all, could atropos really feed on a conspecific to such an extent that it survives? (If no other food is available?)
So so, I would therefore recommend never keeping too many Sphingidae in too small a space.
From what I can tell it seems predatory, I watched one caterpillar actively crawl onto the mesh ( ignoring food plant) and start biting into an l3 caterpillar getting ready to moult. It's started to become a somewhat frequent thing towards any smaller individuals but all caterpillars that are the same size are completely peaceful with one another. Previously I've seen tail horns being bitten off and have pitted it to accidental consumption but now it's seeming a bit more predatory in intent. I'll be curious in seeing if it's the same when my Sphinx ligustri pupae hatch out and hopefully lay some eggs.
