A Spring Tastingby Michael RossmanIt's a spring day, pulsing so with balmy warmth that I can't stand doing science indoors any more than my first-graders can. So we take to the sidewalks outside, after I remind them of Michael's Seventeenth Law. "Where there's something to eat?" I intone. "There'll be someone to eat it," they respond in dutiful chorus. "Okay, everything's been growing," I say, "let's go see who's been eating what." Right outside the school, the dandelions bush up vigorously behind a low wall, spread out enough to let each child choose a broad leaf and examine it carefully. Oohs and excitement, the undersides of the leaves are rich with colonies of aphids. I take a large scrap of white paper and show them how to shake the living plants vigorously above it. A snow of aphids falls to the paper surface. We study them in the light, admiring the way their little bodies are pumped full of the plant-juices they have sucked. "Why do they live on the undersides of the leaves?" I ask, invoking Law Number One ("There's always a reason.") Darby says it's for protection from the sun, David thinks protection from predators (though birds seem too large), Erica says the underside of the leaf is softer. Their reasonings are all sound. I ask them to look more closely at the dandelion leaves, to see the typical damage that aphids leave, the light stippling of dead-cells where their sucking lancets have pierced. Most of the aphids are green, but some are black, amber, tan. "Why?" I demand. "Maybe they're different kinds?" ventures Heather. "I don't know. A cat can have kittens of many different colors. How could you find out for sure?" They puzzle this until Darby offers, "See if their children are the same as them." It's a good-enough answer, making explicit the idea that being of-a-kind means breeding true. I don't want to trouble it with complications, but I can't resist telling them how aphids sometimes reproduce by parthenogenesis, the females yielding fertile female eggs without male intervention for generations: "Girls making girls, no boy babies. Isn't that neat? Now take a taste of the dandelion leaf." Most of them nibble a bit. No one likes it very much, among these city kids unused to strong-flavored greens. They listen skeptically while I say that young dandelions can be a spring salad delicacy. But we do find, on a second tasting, that the younger shoots and leaves taste less strong; and Erica notices then that the aphids seem particularly to like the younger tender stalks. Across the street, on the shady side, gleams a bank of sour-grass in flower, its bright yellow blossoms floating like butterfly advertisements for the piquant taste of its stems. This Oxalis grows wild here but not in the town where I grew up, so it was my son who introduced it to me when he was four, having learned about it himself from other children through the processes of kids' culture, quite independently from adults. All the kids in my class know it already, and are glad to rush over to this lush bank. "Hands off! Don't pick! You barbarians!" I yell, trailing behind. "You're here to study it, you can eat later. Now look closely, find out who's eating it." They bend to the bright yellow petals, find them flawless; mistake the spots on the leaves for disease; and then see that the spots form a consistent pattern. "So who's eating this?" I repeat. "Nobody," they say. Then Jennifer discovers an aphid. "Well, hardly anybody," offers Darby. I brush off my paper surface and start again, holding it beneath the sour-grass as they shake the slightly sticky bunches vigorously. When we look at the paper in the sun, it's true: there's almost nothing, just a couple of aphids. "So how come nobody's eating the sour-grass?" I ask. "Because it tastes bad to them?" ventures Meredith. "Does that sound plausible?" I ask the class. They agree that it does. "Okay, now turn the idea around," I say. "Why does this plant have that odd taste?" "To protect itself from being eaten!" several exclaim. "Yeah, but the dandelion tasted yucky," says Ezra, always out to be the spoiler, and here quite right. All I can say is, "Okay, we can't settle a question like this by looking at only two kinds of plants. We'll be looking at more, just keep track." We make a brief stop at an ivy patch. On the broad leaves we see a few relatively large holes, scattered here and there, obviously the work of snails. But the brighter-green leaves of this year's new growth have very few holes so far. It seems that youth doesn't make them any more palatable to the snails, or to anybody else. When we shake the leaves over the paper, nothing at all falls down. The tips of leaves we nibble are sour. As we move on I share survival information: Ivy berries are poisonous. Infants particularly need protection, could die from eating them. Next stop is an untended sidewalk strip gone to one of those benign, common, round-leaved weeds whose names I so easily forget, I think it's a mallow. Again we go through the ritual of inspection, each child bending to scrutinize his or her chosen leaf. Some of what we find can be shaken onto our paper -- not only a big crop of aphids, but a few strange torpedo-shaped insect nymphs. Besides this, there's all sorts of damage on the leaves -- not just collapsed cells from the aphids and small holes from whomsoever, but also odd yellow and cerise spots and growths, little galls caused by some plant virus or other infection. The excitement, though, is in the little striped nymphs, who scurry actively over the paper seeking shade to relieve the sun. Since we've seen ladybug beetles here and there in the neighborhood the connection is plausible, but it's still hard for them to feel so intimate a relation between those beautiful toy-like beetles and these bristling, black-and-red nymphs. It's easier, though, for them to imagine the nymphs as the fierce predators that they are. Indeed, watching them scurrying among the passive plump bodies on the paper, this relation is quite clear: With all those aphids to eat, someone had to be eating them. As for what the aphids have been eating, we nibble the leaves ourselves, and find them to be pretty blah -- but inoffensive enough to have been used by the Native Americans here, as the local plant books say -- and then we move on. Right next door is a patch of ornamental juniper. We dally on the path of our inquiry as we admire the webs of the peculiar spider species that frequents juniper hedges here, and try to coax the spiders forth by tickling the margins of their webs with straws, as one often can. After discussion, we agree that the spiders aren't eating or hurting the plant. So we bend to investigate its strangely-shaped foliage. There's no trace of damage and nothing's on the leaves, but Ben and Darby find a few small groups of a different kind of black aphid on the stems here and there. Shaking boughs over our paper yields nothing more. It seems that hardly anybody likes juniper except these special aphids, who are sparse. As some children break off tiny tips from the foliage and prepare to taste, I explain what gin is, and tell them that its taste comes partly from the use of juniper berries. Then they nibble the sprigs. Outcries, much spitting and fussing. It does taste pretty bad! "That was mean of you," Erica accuses. "That's why I said to nibble only a tiny bit. If you chew some sour-grass, it'll take the taste away," I say. "Okay, on to the lot. But wait for me at the edge." They break away and tear along the sidewalk, whooping, to the vacant lot that is so often our destination when we go walking. There's nothing special about it, the absentee owners even torture it with bulldozers every now and then -- yet still its life springs back, a modest, inexhaustible treasure. This time what it offers is lush grass and spring weeds, and we pause at the edge to sample the main kind of grass, inspecting its leaves. A new sort of lesion appears, tiny shiny cellular patches -- teaching us to recognize the characteristic damage of thrips, whose tiny slim black bodies appear in profusion on the sheet as we shake the grass-tufts. There are some scattered leafhoppers and aphids too, but the thrips predominate. As we pull grass-stems from their sockets to suck the sweet stalks, we decide that the thrips have good taste. With the grass assessed, we move on to the lot's interior, dotted with patches of a clover with tiny yellow flowers. Someone's sure been eating these leaves, they're positively riddled with holes. "Snails?" someone ventures. The holes are too small. "Leafhoppers?" "They're suckers, they don't leave holes," Mark ventures his opinion, "only dead spots maybe." We scrabble in the duff at the base of the clover stems. Sure enough, we find a few slugs, they're likely culprits. But why there are no slug tracks on the leaves? And so few slugs below, waiting for night's damp air? "Many people drink clover teas," I inform them, as David holds the paper and Erica shakes a hank of the foliage above it. "Cows like it too, and horses." What showers down upon the sheet surprises them, and me too, for the slugs had still seemed likely as culprits. But here are two jillion fat little crescents, grubs or caterpillars, bright green and slightly veined, so nicely camouflaged to hide in the buds and growing leaf-clusters of the clover, that we're all delighted. There's quite a lot of meat here, even though the largest are scarcely half an inch long. I think they're more likely to grow up as beetles than as butterflies, but we'll have to come back later and see when they're emerging from their chrysalises. But there's no doubt about the larger grubs curled near the roots of the clover -- we've identified them as beetle larva long since. Sow-bugs and pill-bugs too abound near the roots. It seems that everyone likes clover. "So who's eating all the caterpillars?" asks David. We look again for small predators, but see nothing. It's likely that parasitic wasp larvae are inside many, but I direct the children's attention instead to the probability of birds, absent as long as we're here. There's one last stop before I release them to roam on their own through the field for the rest of our hour abroad, We gather near the broad swathes of succulent triangular stems topped by tiny white bells -- a sweet wild onion with a garlic taste that grows in profusion here and there in our town, a familiar delicacy to many of the kids. "So what should we expect," I ask, "about who's eating the onions?" After so many examples, the biological logic is clearer, and they come to quick agreement: "Probably nobody." "How come?" I challenge. "Because of the chemicals in the leaves," says David. "Even though it isn't bitter? Even though you like it?" "Uh huh," he maintains. "It tastes weird, and insects don't like things that taste weird." "The aphids liked the dandelion." "The dandelion tasted strong, but it didn't taste weird." Damon and Amanda, who've been silent throughout, ask to do the shake test, to my pleasure. And David turns out to be right, there's hardly anyone shaken loose from feeding, just a stray aphid or two, plus some mysterious white exoskeletons, shed by someone very small. "That's the end of the demonstration," I say, "okay, you're on your own." Damon and Amanda are disappointed, they still want a chance to get a good haul of insects. I point them toward a distant clump of sweet-pea to sample, and then send Darby and two others, serious students who've lingered behind, to go along with them to see if it indeed is true, as we have found so far, that each different kind of plant has its own characteristic population of predators. And I am left in the spring sun amid the fragrant grass to think what a pleasure it is to live and teach in a town with gardens and vacant lots still; and how rich is the world. And what pleasure too to teach in this way, seeing how much can be done how naturally through simple disciplines of simple observation, moving from one thing to another as the world affords.
Return to: Top | Lessons & Reflections | Home > |