The excrement or droppings of insects, especially caterpillars and other larvae, often visible on plants they infest.
From German 'Frass' meaning 'food waste' or 'refuse,' used in entomology since the 19th century to describe insect feces.
Frass is actually useful to scientists—by identifying frass patterns and contents, entomologists can tell what insects are feeding on plants without ever seeing the insects themselves, like detective work with bug poop!
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