Caterpillars can come into your indoor gardening by creeping in through holes in screens, open windows or cracks in the walls. Check all your indoor garden plant shoots, leaves, stems, buds and flowers for caterpillars. Some caterpillars can't be identify because of their green in color. Hand-pick caterpillars and drop them into a bucket of soapy water. Apply Bacillus thuringiensis to your plant.