A few years ago I wrote a few posts about a plant the Hairless Hunk had given me. Becs identified it as Jimson weed (Datura stramonium). Several respected sources informed me that the plant is very dangerous, that every part of the plant is poisonous, and that no animal or insect is known to eat Jimson weed. But then I found a huge tomato hornworm caterpillar eating it. The caterpillar was covered with cocoons of the sphinx moth. (That post is here. scroll down to the photo of the caterpillar.) The sphinx moth lays eggs under the caterpillar's skin, the moth larvae eat its insides, and then emerge to pupate on its back. (Bleck. How was that moth still alive and moving? A question still to be answered.) I wondered if the caterpillar was trying to commit suicide.
Well, the past few days I've been watching a lot of documentary videos on YouTube about plants, how they communicate with each other, how they protect themselves, and so on. Some people are saying that plants are intelligent and aware, others say no, it's just genes and chemical and electrical, just the way they're built, and so on. But, uh, look at us and animals. It's just genes and chemicals and electrical with us, too, but we consider ourselves and animals as having intelligence. Maybe we need to look deeper into plants and expand that definition a bit.
There was a drought somewhere in Africa, and Kudu antelopes in a preserve were reduced to eating acacia leaves. Kudus eat acacia leaves normally, no big deal. But the kudus started dying. They were poisoned. It turned out that the acacia leaves being eaten were extraordinarily high in tannins.
It wasn't because of the drought - trees well outside the reserve had normal levels. Scientists figured that predation had caused the trees to react by producing more tannins to discourage munching. Then it got more interesting. Trees just outside the fence, that had not been chewed, were also high. So -- it's not being chewed that causes the tannin in those trees.
Turns out that the trees under attack had put out a chemical signal into the air that alerted other nearby trees of the danger, and they, too, upped the tannin in their leaves, even if they had not yet been chewed, and also spread the signal.
That's called communication.
Back to the caterpillar. Another video mentioned the wild tobacco plant (which is related to the Jimson weed) and how it produces poison such that no insects eat it. EXCEPT the hornworm caterpillar! Hornworms are immune to the poison! Wow! Confusion cleared. That explains the hornworm on my Jimson.
But then it gets weird. When it feels itself getting munched, the tobacco plant (and, I assume, Jimson weed) puts out a chemical signal into the air that attracts (ta rah!) braconid wasps. Who (slowly) kill the caterpillar.
Then it gets even weirder. The wild tobacco plant normaly has flowers that bloom in the evening, and are pollinated by moths. But if too many of those moths are sphinx moths who are laying eggs and threatening the plant, the plant puts out another signal, and all the tobacco plants in the area switch their flowers to day-blooming long-throated blossoms that attract hummingbirds, not moths.
(Actually, back when the plants "called" the braconid wasps, maybe they should have called a big bird, or some lizards, who'd eat the caterpillars right off. Those wasp larvae are too slow.)
I often tease people who smugly say they never eat anything with a face with "No, you'd rather tear the arms off a living broccoli just because you can't hear them scream". Turns out they DO scream. We are simply not equipped to "hear" them.