I never gave these critters much thought. They appear this time of year, hanging from invisible threads on the eaves, or suspended from low tree limbs in the backyard.
They land on the car, or on a sweater.
You'll likely find their sudden appearance in spring coinciding with the emergence of tree leaves, which they like to eat. Right about this time, migrating warblers show up in Princeton to feast on the inchworms high in the trees.
As spring moves northward, awakening forests as it goes, the warblers follow the wave of new growth, powered by solar energy transferred from tree leaf to inchworm to beating wing.