I've got a houseplant thats been outside in the shade during the summer months and decided to bring it in last month, and when i got up in the morning there was a sprinkle of black bits around the plant up to 6 inches away on the window sill. After close inspection of the plant i found a very small caterpillar under one of the leafs so i snipped the leaf of with caterpillar removed the both to the garden, no more droppings . Under my buddleia that hangs over the path is the same droppings but a tad bigger, caterpillars again.