Prickly Caterpillar annual grows easily in full sun

The soft, rich soil around Stockton, Calif. is ideal farmland except that tractor tires often sink hopelessly into the muck. Benjamin Holt used wooden tracks bolted onto chains to prevent the tractor from sinking, and it worked. Photographer Charles Clements noted that the slow-moving machine seemed to inch along like a caterpillar, and Caterpillar Tractors was born.

Garden caterpillars can grow as quickly as the birth of a tractor empire, with tobacco hornworm caterpillars growing ten thousand times heavier in fewer than 20 days.  Many caterpillars eat toxic plants, but instead of dying, just retain the poison in their own bodies, making them toxic to predators. With up to 4,000 muscles, each innervated by one or two neurons, and 12 eyes, caterpillars are fascinating for gardeners, but would you really want to eat one?

Well, not an insect but a plant, the Prickly Caterpillar (Scorpiurus muricatus) named for its hairy, contorted pods that curl up like Mr. Holt’s slinking tractor. This annual legume has small yellow flowers much like a sweet pea. It is native to southern Europe and grows easily in full sun. You can either start the seeds indoors and transplant after all danger of  frost has passed, or wait until warm weather and direct sow them in the garden.The plants are small enough to grow in pots.

Sow the seeds one-quarter inch deep, six to 10 inches apart in rows 18 to 24 inches apart. Prickly Caterpillar germinate in 10 to 14 days. Sow extra seeds because the seeds have low germination of as low as 30 percent. Once the plants have a set of true leaves, cut out any extras with scissors so you do not uproot the remaining plants.

Water lightly throughout the season, and never keep them soggy. They can tolerate a wide range of soil, preferring soil pH between 6.1 to 6.5 (mildly acidic) or 7.6 to 7.8 (mildly alkaline). Seeds for Prickly Caterpillar are sometimes available from some local garden centers or nurseries or Seedman (online at www.seedman.com) and Seed Savers Exchange (www.seedsavers.org, Seed Savers Exchange, 3094 North Winn Road, Decorah, Iowa 52101, Phone: 563-382-5990.

The trailing plants are nice enough to use as a ground cover. Because they are legumes the plants will trap nitrogen from the air and release it into to the soil as a free fertilizer.

Prickly Caterpillar is an ancient heirloom novelty mentioned by Vilmorin in the 1800s. Some herbalists use Prickly Caterpillar extracts because of the plant’s high concentration of phytoalexins.

But it is really as it always has been grown mainly to hide the curled pods in salads for shock value. The pods would have to steamed to be truly edible, though even then they are not especially delicious or flavorful.

You may want to let some of the pods go to seed for next year. Let the pods dry completely on the plant. Over a large plate break each pod and let the seeds fall onto the plant.  

And the real garden caterpillars? Well, they stop eating, hang upside down from a twig or leaf, and magically transform their bodies from caterpillar to moth or butterfly. Oh, and they get the energy to do all this because the caterpillar digests itself by dissolving its own tissues to use as food. While that does sound delicious, I think I will stick with the salad.