THEY’VE ALREADY STARTED on the fall cleanup. The tobacco hornworms, or Manduca sexta, that is–who love to chomp late in the garden season here on my haze of self-sown Nicotiana, or flowering tobacco–the annuals I let spread themselves around for my visual pleasure and to attract hummingbirds. But how do I know these voracious giant green caterpillars aren’t actually their close cousins the tomato hornworms, Manduca quinquemaculata (since both species will eat Solanaceous crops such as tobacco and tomato)? It’s all in the stripes, and the “horns.”
The tomato hornworm and tobacco hornworm both have angled white markings on their sides, but the tobacco hornworm’s seven marks just go in one direction, and the white is edged in black; the tomato hornworm’s eight marks per side are each more like a chevron, or “V,” with no black edge. The other big difference: Tobacco hornworms’ “horns” (which look like a tail) are usually reddish; the tomato hornworms’ are black or blue-black. (Oddly, I don’t have a photo of the tomato hornworm, but you can compare them on this University of Florida web page.)
That University of Florida Entomology site has photos of the very similar-looking sphinx moths that each one becomes, too.
I think the one just above was more recently “hatched,” because its body was still dark-colored, but I’m not certain. Maybe he’d just been smoking and got all sooty? (Kidding.) You can see all the life phases–caterpillar, chrysalis, sphinx moth–here.
I have to say, I’m violent when one of these guys is eating my tomatoes in early summer, and it’s all “off with their heads” over here then. But in fall, as the garden unwinds anyhow? Eat all you want; the buffet is open. Go ahead and get fat and juicy, tobacco hornworms–and maybe some bird will eat you!
Usually I break off the stem and give them to my chickens, but the other day I saw one of those hornworms (not sure which one!) on my tomatoes that was covered with what looked like grains of rice – the larva of a parasitic wasp. So I let them do their thing!
I had no idea there were two so similar varieties. Must go back and re-identify the ones I have photographed.
What pretty “worms”! We don’t have native (or any kind) of tobacco here in Australia (although an old Hippy American man that we know down the road seems to have some growing on his property…) so the hornworms would be severely hungry and with our short growing period in Summer (we are in Tasmania Australia), the tomato hornworms would have problems as well. Aside from the slugs that come out in force when we lock the duck up in her coop for the night, we don’t have too many problems with grubs, worms etc. here as the chooks are free range and deal with most of them. I might just have to get that lazy duck out on a string at night to deal with all of those slugs! (Or get out there and collect them up in a bucket with a lid for her breakfast…). I love your integrated pest management stragegy and saving your energy for the food pests is our ethos as well. Thank you for those lovely photos and another great post :)
I agree: off with their heads!
Early summer a few of these can quickly chop down some tomato leaves – and also fruit.
One of our batches of chickens didn’t used to eat them so hubby would squish them on the ground which always grossed me out. Luckily, a different batch of chickens would eat them, so no squishing. :}
We’d not even seen any in the last couple of years.
I worked with tobacco hornworms for many years. When the eggs hatch, a tiny larva emerges. As it grows, it molts its skin, and becomes a larger larva. These stages are called instars. The hornworm has 5 instars and, after the 5th instar, it pupates. After a period of time, the moth emerges. The larva in the second picture has been injured and the black is its blood (hemolymph) which turns that color when exposed to air.
I just figured out the difference between tobacco and tomato hornworms myself – had one eating my tomato plant but the lack of chevron patterning had me hunting further afield for ID. I moved it off the tomato and tossed it over the fence where it will either find other suitable forage or perhaps become bird food. I appreciate your philosophy when it comes to pest management. My husband and I disagree about when/if to spray – one of the few ongoing conflicts between us. He’s a physician and the West Nile virus showing up in 1 of 4 mosquitoes in our area crossed a line.
I had a picture of a tomato hornworm with the little wasps connected to it. So yucky. If I find it I’ll send it. The wasps kill it , but fortunately i don’t know how.Do they suck it to death???
Hi, Alice. Those are probably braconid wasps (which lay eggs on the hornworm). They are called parasitoids, and usually kill their host in the process of using them as a place to lay those eggs. As the eggs (which are actually inserted slightly under the skin of the hornworm) hatch, the newborns use the body of the caterpillar as their first meal. Like this.
Those wasps are braconid wasps. Here’s some info on them including how they kill the worms: http://aggie-horticulture.tamu.edu/galveston/beneficials/beneficial-04_braconid_wasp_on_hornworm.htm
Geat – Thank you
Every couple of days we head out to our tomato patch and have a picking party. Once we get a small bucket full, we dump them out for our chickens and they go wild eating up every last one and usually within just a couple minutes. Then the chickens patiently wait the next time they see us at the tomato plants because they seem to know what is coming.
Lovely image, Nathan (and smart chickens). It’s that time of year, for us people and for the chickens. Delicious harvests, lots of goodies. See you soon!
I don’t have a garden, just a patio plant or two, but I picked at least 18 of these worms off of my plants. I bought a bottle of peroxide and when I pick them off I put them in this and they die almost instantly. it s nice to see them shake
other than turning into hummingbird moths what role do they play in the ecosystem?
Hi, Terri. You can read about it in more depth on the Encyclopedia of Life, especially the section called Benefits. All of this is food chain and cycle of life connectivity is so complex, of course, because it depends on where you are and whether the plants its moth pollinates are present there…or its relationship to certain weeds is relevant where you are located, etc. And then there is this: I do’t know if we know the answer completely yet for every creature! : )
Great – Thank you
I am much crueler… When I find a tomato hornworm- being skittish I lop off the leaf with him on it & take it out to the road to be squashed by a car. Can’t stand those things. Need to check daily for them- because if you skip a day – your entire tomato plant will be missing !
I don’t kill them. I have more than enough for them and me and many times, they are already parasitized by a wasp so there is no need. Also, the moths are gorgeous and a joy to watch.
I don’t kill parsley worms either. They turn into gorgeous Black Swallowtails. About the only thing I go out of my way to kill are BMSB and Japanese beetles.
I have sacrificial tomato plants that I move them to. Just plant a few extra. Move them by snipping the branch. Love to see the hummingbird moth they become.
That caterpillar looks like its got npv which is a virus they get that dissolves their body. If you dont want caterpillars anymore, a gross way to have that happen is to mush that one up and mix it with some water. Put the solution in a spray bottle and spray your plants. All the caterpillars that find themselve on that plant will contract it and die. I’m not sure how long this method will work for, but it’s worth a shot imo.
Wow, Rk, who knew? Thanks!