Tomato and tobacco hornworms are not worms, but caterpillars, and both are larvae of the Sphingidae family of moths. The tobacco hornworm is Manduca Sexta and the tomato hornworm is Manduca Quinquemaculata. They are difficult to tell apart. One way to identify the difference is by the color of the “horn” on the tail. The tobacco hornworm has a red horn while the tomato hornworm has a black horn. The tobacco hornworm has seven diagonal white markings on its body while the tomato hornworm has seven v-shaped white markings.
While the hornworm is considered a “specialist eater,” you can find these little green tanks chewing on other plants in the nightshade, or Solanaceae family of plants. Yes, tobacco, tomatoes, potatoes, eggplant, chili and bell peppers are related! The little devils are camouflaged and stealthy and difficult to find and eliminate.
My video discusses using an inexpensive 405 nanometer (nm) blue-violet -actually an ultra-violet wave-length 50 milliwatt laser pen (I buy off eBay for just a few dollars)- to fluoresce the hornworm at night. Hornworms fluoresce blue-white while tomato (and most other) leaves will fluoresce a deep purple color. This is because chlorophyll will begin absorbing light energy in a wave-length close to the pen's wave-length. There is an excitation-emission peak at around 450 nm, one of several peaks in the 350 nm to 700 nm band. The light energy is re-emitted as fluorescence and heat by the leaf under certain conditions, such as laser stimulation. By the way, hornworms don't like the laser and will quickly rear up. That movement also helps in finding them. I suspect that finding a more powerful pen or hacking an existing one -to increase its power- would actually incapacitate and/or kill most insects. Hmmm.
Whether you are a hobbyist like me or a professional farmer, these little green terrors can make for a bad day. Hornworms cause billions of dollars in crop damage every year. If you're trying to avoid using pesticides, then all you can really do is foliar spray with plant-oil based products, use various home remedies (watch my video) (read my blog), and start picking! Picking them off and crushing or drowning them is the only sure remedy if you are averse to chemical poisons.