In my personal experiance, i use diamond lath on the outside of my grow room, it allows aenough sun in but is small enough to keep out butterflies and moths and such. ive had whole crops munched on and destroyed, once i put the lath on ive ran one crop and didnt have one worm. its better to be proactive than reactive. Again there might be differant kinds of worms but where i live in So Cal the diamond lath works perfect, well worth the investment.