The summer heat has gotten sullen. Zucchini and tomato plants thrive in the sweating air. My zucchini explode at dawn with gigantic yellow blossoms, and before you know it inflate their fruit to the size of dirigibles. I walk from neighbor to neighbor offering these fine logs of food, good only for zucchini Parmesan and zucchini bread. My brother Bob, who lives on a farm in Wisconsin, warns me to lock my car if I drive to Kenosha this time of year or people will stuff it full of swollen orphaned zucchini.
The next day at noon I sat on the back porch having tea. I looked for the hornworm and found it still feeding on a reduced plant, but sick somehow. Over the tapestry of its flesh was a pox, dozens of yellowish brown marks. As I watched over the next few minutes they deepened in color and distinctness, now hundreds of spots. And then, to my horror, they swelled. First a few and then scores at a time came to a head, like ripe pimples–translucent yellowish lumps.
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But peace had come to the hornworm and the grubs. Nothing moved. I waited, trying to remember what these cocoons might hold.
Later she called me to say that the hornworm, cocoon, and wasps were all gone, the whole drama perhaps ended by a hungry robin. Only the vine and vase remained.
The prairie fringed orchid is endangered, but tomato hornworms are thriving in backyard gardens, even though they’re routinely innoculated by braconid wasps. There are dozens of strategies these wasps use to parasitize caterpillars, but they all have the same aim: to transmute caterpillar tissue into wasp tissue. Judging by the size of the maggot brood I watched, my hornworm might have been parasitized by a wasp whose reproductive strategy was polyembryony, in which several eggs are inserted into the tissue of the host. The embryos subsequently divide, like identical human twins, but into numerous identical wasp larvae, sometimes up to 50 per egg.
