American Scientist

Gardens, to me, are magical additions to the landscape. An extension of ourselves, they provide a vehicle for expression, a colorful means for laying out a zone of transition between home and the wild. To keep gardens weeded is judged to be a must, and I have always had the utmost admiration for the gardener who succeeded. As a naturalist, however, I have of late had second thoughts about the fate of weeds. Altogether too often these include descendants of the very greenery that was cleared to make room for the garden, so that it is really quite unrealistic to think of weeds as intruders when in fact it is our ornamentals that are the occupiers. I know the argument is unlikely to win support, but I do want to make the case that the individual weed, or more exactly the natural vegetational mix that is eliminated to lay out a garden, has hidden value.

Laissez-faire Landscaping

If you are near the Cornell campus, do pay a visit to Corson-Mudd Hall, on Tower Road, and have a look at what has been done—or rather has not been done—with the narrow strip of land that slopes down sharply from the sidewalk to the front of the Corson half of the building. Someone had the bright idea of "landscaping" that piece of land by not landscaping it at all. In midsummer one can find a patch of meadow there, a small enclave of wilderness where plant, herbivore and pollinator pursue the chaos of coexistence. There are familiar plants there, milkweeds, wild lettuce, nightshades and morning glory vines, plus an assortment of insect associates, both larval and adult, each a storybook in itself, awaiting only the curious, who with little more than a hand lens can join the ranks of the naturalist explorer.

Corson-Mudd is my home on the Cornell campus, and I have made it a point to spend occasional moments in that patch of wilderness, checking on the bugs and their doings. Literally within yards from my laboratory bench, I have had the opportunity to catch sight of the workings of nature.

I have vivid recollections. On an Asclepias syriaca at the site, a common milkweed, I noticed the presence of a beetle I have long liked because of its unforgettable name—Tetraopes tetrophthalmus—a member of the long-horned beetle family. Milkweed plants are chemically protected by the "milk" that oozes from them when they are injured. The milk is chock full of noxious chemicals and coagulates into a sticky mass when exposed to air, with the result that there are few insects that venture to bite into milkweeds. Those that do have a special way of minimizing their exposure to the milk. Just before settling in to munch on a leaf, they subject it to culinary pretreatment. Using their mandibles, they cut through one or more of the leaf veins, getting out of the way as the milk oozes from the incisions. The entire portion of the leaf beyond the cuts is thus drained of milk and rendered edible. Tetraopes is a vein cutter. It cuts through the midvein about three-quarters of the way up the length of the leaf, before eventually proceeding to eat the leaf tip. Leaves fed upon by Tetraopes are easy to spot, because they are missing the tip and have telltale incisions on the midvein. It was by such evidence that I became aware of the presence of Tetraopes in that wilderness garden.

Another resident was a little tortoise beetle, Deloyola guttata, which I found to be fairly abundant on a morning glory vine. Distinctly turtle-shaped, this black and yellow, partly translucent beetle shared the food plant with larvae of its own species. The larvae of Deloyola are called trash carriers, and the name is fitting. They have the peculiar habit of retaining their feces on a two-pronged fork that is attached to their rear and projects forward at an angle over their back. The fork is typically covered with the accumulated wastes, which form a pasty mass held like an umbrella over the body. The fecal fork, as it is called, is a maneuverable device. The larva can tilt it to the right or left, or forward over its front by lifting its rear, and can thus use the fecal mass as a protective shield. Touch the larva anywhere along its flanks with a slender probe, and you will find that it responds instantly by interposing the shield between itself and the probe. Ordinarily the larva probably uses the shield for protection against ants and other enemies, including perhaps even tiny parasitic wasps. Watching the larvae maneuver their shields as they put their overhead sewer system to use was pure fun.

Dressing to Disappear

Last summer I had the good fortune of spotting a little caterpillar at the site, an insect that is really quite common in our area but is known to few because it is so spectacularly adept at achieving invisibility. The caterpillar escapes detection as it frequents various flowers because it dresses up as a flower. It cuts pieces of petals from flowers and fastens them onto its back with strands of silk that it secretes from special glands, thereby succeeding in entirely covering itself. I found the caterpillar, which goes by the elegant name of Synchlora aerata, on flowers of the common fleabane, Erigeron strigosus, one of several composite plants that had gained a foothold in the patch.

Synchlora is beautifully adapted to perform its vanishing act. It has tiny bundles of spines protruding from its back, to which it fastens the silk it uses to tie down the petal pieces. It appears able to sense when the pieces need renewing. Because the larva carries no vase on its back, the pieces wilt with time. The larva renews them at intervals, ensuring that its protective cover remains fresh and appropriately floral in appearance.

When the larva pupates it crawls from the flowers to a more central location on the plant. There it eventually spins a loose cocoon. It weaves its petal cover into the fabric of the cocoon, and as a consequence blends in beautifully with the background. The delicate moth that emerges from the cocoon is a pale yellowish-green.

Everyone should have a patch of wilderness within easy reach. Gardeners should give serious thought to whether they might wish to let a portion of their garden revert to wilderness. I am not calling for the replacement of the ornamental garden. Just for the incorporation of a patch of wilderness into what we now devote solely, with justifiable enthusiasm, to the display of magnificence. The patch could introduce a magnificence of its own—the magnificence of reality, played out at close range, within visual access, and to the immense benefit of the observer. The patch would require neither weeding nor insecticidal treatment. The insects, in fact, would be part of the show. There would be no price of admission, or predetermined performance times. Just entertainment and the opportunity to wonder....