IF you see white speckles on the worm that is a parasite and it is recommended to leave them so the parasites will continue feeding and survive.

IF not I just cut the worm with scissors. I don't usu. see more than one in my garden every couple of yrs.

Last year I saw plenty. Once these spread they wreck havoc. I have not seen the other kind yet.

gumby_ct's white speckles are oval cocoons belonging to a tiny wasp (the cocoons are about 1/8" tall, so it really is a tiny wasp).

By the time the cocoons appear, the hornworm is beyond moving and the wasp larvae are no longer feeding, but it's advantageous to leave the caterpillar in place so the wasps can emerge and begin their lives' work of keeping more hornworms from becoming moths and breeding another generation of worms.

I tend to see about four hornworms in the same area at a time.