Caterpillars are a fairly common pest for cannabis plants. The most common are gypsy moth caterpillars. A gypsy moth is a small gray/brown moth that will lay egg sacs and cover them in hairs in dark dry places like your top soil, under leaves, in piles of dry mulch, or in other dry dead foliage. The moths themselves aren’t much more than a nuisance but once the eggs hatch into tiny caterpillar larvae you have a problem.
Caterpillar larvae live in your soil and only come out to feed at night and are pretty hard to see until they fully mature. An easy way to look to see if you have any is to look under your leaves and around your stems and look for tiny silk like threads that they use to climb up and down to feed and hide in your soil. You might even see tiny little white larvae wiggling around in the soil or on leaves before they adjust to the lighting schedule in their environment.
To prevent them a weekly spraying of neem oil or garlic and pepper foliar spray will keep the gypsy moth away before they even get a chance to lay their eggs.
If you happen to get an infestation don’t worry. There are natural treatments available.
The most effective is BT bacteria (not to be confused BTI) that will kill the larvae in the soil before they have a chance to get your plants.
A neem drench is also effective at killing and preventing caterpillars.
The last method is a garlic water drench if you can’t get BT or neem. It is effective but it will increase the acidity of your soil and should be a last resort.
Hope this helps some of you guys. Happy growing. 
