I'm just guessing here, but they may be eggs. There are many species of insects that lay their eggs on a stalk or filament. I think the idea is to keep them dry and out of the way of predators.
The good news is that they are probably harmless. The unfortunate news is that they are likely the eggs of a lacewing, a serious predator of aphids.
From: here:
https://www.whatsthatbug.com/2012/04/02/probably-lacewing-eggs
Insects in the order Neuroptera often lay eggs on stalks. The larvae of Lacewings are fierce predators known commonly as Aphid Wolves. It is believed that they have adapted to laying eggs on stalks to help reduce the possibility that hatchling Aphid Wolves will devour one another upon hatching.
Maybe... maybe not.