Munch, munch, munch

Friends, gardeners, farmers! I come to praise the tobacco hornworm, Manduca sexta, not bury it. You, on the other hand, may be quick to go snicker-snack! That I leave up to you and your conscience.

I had been wondering why my sweet frying pepper, a first time plant for me, had not made any fruit this year. It took a long time for this plant to get past the transplanting stage, but then it started to grow taller, branch, and open a number of small flowers. I was optimistic, but I got bupkiss, or rather, this caterpillar.

While this eating machine may not be the only culprit, it certain is one of the pests of plants within the nightshade family, Solanaceae. This includes deadly nightshade, but also a remarkable collection of non-deadly, indeed, eminently edible, veggies, like potatoes and tomatoes. (Tobacco, I suppose, is only eaten metaphorically.) A day later, I found an even bigger example of this caterpillar on the tomatoes, which makes sense. The female moth searched out these food plants to lay her eggs upon.

Note here the three pairs of thoracic legs, all clustered together near the face. In the other images, you can see the four sets of anterior prolegs, and bringing up the rear, under the horn, the anal proleg. The eye-like structures on the body are spiracles, or respiratory pores. The white stripes are a good diagnostic identifier; the somewhat similar tomato hornworm has a chevron pattern.

The horn, a characteristic shared by the larval stages of sphinx or hawk moths – of which there are 70 species in the eastern U.S. – is particularly well-developed here. This caterpillar will, after stuffing itself, typically pupate and then emerge as a Carolina sphinx moth. Unless…

I first noticed these hornworms a couple of weeks ago, before my Internet and phone service vanished (fuck you, Verizon). A bit later, the first caterpillar, on the pepper plant, turned out to have been taken over by its natural enemy. A parasitic braconid wasp, Cotesia congregata, uses the live body of the caterpillar as a host for her eggs. Dozens of eggs, which are injected into the caterpillar. The eggs hatch, the larva grow, and then tunnel out of the caterpillar to spin these tiny cocoons. The caterpillar dies a slow and presumably agonizing death, as it is eaten from the inside out.

5 Responses to “Munch, munch, munch”

  1. 1 Sara September 12, 2010 at 8:44 am

    Um, so where’s the praise, then? Was hoping to hear that, though these insects destroyed your crop, they have this and that benefit. Unless you’re writing from a parasitic wasp’s pov.

    • 2 mthew September 12, 2010 at 10:01 am

      Ambiguity ruled this post. Found them beautiful, yes, and hope the pictures convey some of that. I admit that I am mostly starstruck, fascinated, by my discoveries (which of course were discoveries years ago for others, luckily, so that I can raid their knowledge) here, and post them with as much thought as a celebrity watcher. That we humans too should enjoy this species’ preferred food presents something of a dilemma for us — and vegetarians, whose lifestyle choices necessitate the slaughter of billions of invertebrates — because it too obviously plays a role in the tangled web of life.

  2. 3 Makiko September 13, 2010 at 9:53 pm

    What a beautiful! I saw 6th of photo is first time! I didn’t know.
    Thank you mthew.

  1. 1 City Habitat « Backyard and Beyond Trackback on July 17, 2011 at 8:05 am
  2. 2 Nasty « Backyard and Beyond Trackback on February 12, 2013 at 7:10 am

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