If you plant tomatoes in your garden every year, it is highly probable that you have come across more than a few tomato hornworms or tobacco worms. These are fat bright green worms with diagonal stripes. If they make it to the metamorphosis stage of life, they eventually will become hawk moths.
If you see these big juicy worms on your tomato plants, simply pick them off by hand and drop them into some soapy water. However, if you come across one that has small white protrusions along its back, leave it. This worm is acting as a host for the larvae of a tiny parasitic wasp. Harmless to you and me, these larvae will feed on the hornworm. Eventually, they will emerge from the tiny cocoons and move on to find another hornworm to complete their own life cycle.
The hornworm that is playing the role of the host is of no threat to your tomato plants at this point and will help to increase the population of the parasitic wasps. Which in turn will control the hornworms and prevent the decimation of your tomatoes. Just a prime example of mother nature doing what mother nature does.
NOTE: If you don’t want to just dump the hornworms that are not hosts, take ”em fishin’! The bass will love you.