Question

Can you describe the caterpillars? What crops are being affected?

If you don't know what the caterpillars are, you risk killing off beneficial pollinators in the form of butterflies and moths. If you don't have a plague then hand picking is effective, however for more widespread issue Bacillus thuringensis, a biological infectant is quite effective over a wide spectrum of larval stage insects.

BT kills them when they ingest it, Citrus sprays will kill on contact, and releasing Trichogramma Wasps are some organic controls. The preceding answers are excellent, since they consider the beneficial insects that will be killed. I especially enjoy the Giant Swallowtail Butterflies that come from a fierce looking caterpillar. Stay natural, David

Another option might be to plant a garden-border plant from the same plant family that is attracting the caterpillars. That may lure some egg-layers & you can deposit caterpillars you pick. One such combination is tomato plants in the food garden & a nightshade vine on the perimeter - beautiful, with small purple flowers & later, red but poisonous berries. With brassicas, you could plant ornamental cabbages on the perimater ...