Sena

Room temperature, out of sunlight, away from any heat source for the cup itself. Warmth makes them grow extremely fast, which burns through the food and stresses them, so a cup on a shelf near a radiator produces exactly this pattern even without a hot van.

And none of the dark ones go to your chameleon. Dead or dying hornworms out and in the bin, same as superworms.

Get the dead ones out now rather than at the weekend. A dead hornworm fouls the cup and takes others with it, and that is how three becomes eight.

Then check the chow. They eat constantly and if it has dried out or been eaten down they starve, so look daily and move them to a fresh cup of food if it is low. Feed off the biggest ones first, which deals with overcrowding at the same time.