Introducing Manduca sexta

Tobacco hornworm caterpillar
In places like North Texas, using the phrase “fell out of the sky” gets quite the workout. Several years back, I talked to a gentleman who worked for an aquarium maintenance company who was klonked on the head by a hatchling turtle apparently dropped by a passing seagull. (Yes, we have seagulls from time to time. For inexplicable reasons, they tend to congregate in Target parking lots at random times of the year.) I knew someone in my teen years who had a great horned owl lose its grip on a gigantic skunk and drop the skunk carcass into her convertible. We get fauna, flora, minerals, and occasional pieces of space junk that drop through the area, and this doesn’t always involve tornadoes or high explosives. I finally experienced this myself when I stopped after a bike ride home from the Day Job and found this beast stuck to my shirt.

For the record, this is the caterpillar form of the tobacco hornworm moth, Manduca sexta. Technically, it’s distinguished from its cousin the tomato hornworm (Manduca quinquemaculata) by the number of stripes on the side of the body (M. sexta has seven on each side, while M. quinquemaculata has eight), but they’re indistinguishable from each other in one respect: both feed on plants within the Solanaceae, which includes tobacco, nightshade, potatoes, tomatoes, and Capsicum peppers, and rapidly strip tomato plants down to the thickest stems.

Tobacco hornworm caterpillar

I have to admit that I’m ambivalent toward tobacco and tomato hornworms for several reasons. Firstly, the adult hawkmoths fill the same niche for night-blooming flowers that hummingbirds fill during the day, and at dusk, the moths can be mistaken for hummingbirds. Not only do the hawmoths hover and fly backwards, but they have a tremendously long tongue for feeding on the nectar in deep flowers such as angel trumpets (Datura stramonium) and moonflowers (Ipomoea alba). Plant a stand of either, and the hawkmoths keep showing up for as long as the flowers keep opening. They also tend to frequent my Sarracenia pitcher plants during full moons, carefully extracting nectar along the lid and throat of every pitcher if given a chance. They even steal nectar from hummingbird feeders if given half a chance.

The other reason I’m ambivalent about the damage they cause is that these are also common hosts for several species of exoparasitic wasps in the area. In every case, the adult wasp lays its eggs deep within the caterpillar’s body, where the wasp larvae grow along with the caterpillar. With one species, the larvae emerge from the body and form cocoons that remain attached to the caterpillar’s body, looking like little spools of glass wool; when the wasps emerge from their cocoons, the caterpillar dies. Another simply rips free from the caterpillar, a la the film Alien, and pupates elsewhere. The real surprise, though, is one species where one to two undeveloped larvae remain within the caterpillar’s body while the others pupate, forcing the caterpillar to remain in the vicinity and protect the wasp cocoons until they emerge or it dies of starvation. Either way, the caterpillar goes out in a rather nasty fashion, but that also gives a chance to its brethren to grow to full size, bury themselves in the soil to form a very distinctive pupa with a long pitcherlike “handle” for the tongue, and then emerge as adults in spring.

In this case, since it wasn’t going to be part of an extended photoshoot and it wasn’t an immediate pest, this one went out onto the Datura plants in my back yard. With a bit of luck, it might come back next year to feed on next year’s flowers. And so it goes.

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One response to “Introducing Manduca sexta

  1. The monsters eat up petunias and ornamental nicotianas, too, which seems rather counter productive as the hawkmoths visit the flowers of those. The adults are pretty darn cool; husband calls them ‘turbo hummingbirds” because they run silently.

    Twice when we were working at a site along the river an eagle or osprey dropped a fish in the yard in front of us. Weren’t sure if it was an “Oh, crap!” incident or if the bird thought we looked like we needed feeding. I’ll take pretty much anything falling out of the sky over that skunk, though- other than frozen urine spears.

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