This is on a pumpkin plant, northern hemisphere October (autumn). It occurred during the night, for sure. Thought it might be a slug trail, but haven't seen any since spring and I would think that it is too cold for them. It is mating season for grasshoppers, and I've seen some of those around.
It appears on a couple of leaves, and also on a upper stem of the plant. Could it be the eggs of some moth, perhaps?
Since this post I found slugs in the evening, despite the autumn temperatures; it may be them.
