On Looking: Eleven Walks With Expert Eyes (13 page)

I could have loitered over the funnel webs for a while, but Eiseman had darted off. An urban walk with Eiseman is decidedly nonlinear: one minute he is beside you, the next he has veered over to a tree pit, or to a piece of street furniture—a fireplug or lamppost—and is scrutinizing its surface for bugs. We did leave the parking lot, but over the next two and a half hours, we managed to cover but two-thirds of a mile. At that rocketing pace—about a quarter-mile in an hour—we could have been overtaken by nearly all the species we saw on our walk, including some of the larvae. This was a typical pace for Eiseman, who, as a healthy young man, takes about ten hours to complete a five-mile hike, waylaid by logs whose undersides need examining and snakes
demanding pursuit. He has spent uncountable hours in a quarter-acre vacant lot in Burlington, Vermont, where he once lived: a few dozen photos for his insect guide came from that single plot.

Over those hours, on the most ordinary of city blocks, we saw nearly all the categories of insect sign mentioned in his book: egg cases (the egg sac of a common house spider along a brick wall); exuviae—a fancy word for the discarded exoskeleton of a fly (a mayfly, attracted to and molting on a streetlight); parasitism (gruesome blowflies overtaken by a paralyzing fungus); droppings (earthworm droppings, a large constituent of what we call “dirt”; jumping spider droppings, black speckles in white dots); webs (“
everything
has a spiderweb on it,” Eiseman advised); cases (spider “retreats”—structures for temporary spider-hanging-about); leaf mines (the work of the oak-shothole leafminer, whose larvae fashion rounded holes as they eat their way into adulthood); galls (small deformities on a grape plant leaf, inside of which we found uncountable secreted orange aphidlike things); mounds (small hills with burrows in their middle erupting out little brown “sidewalk crack” ants); and even sign on vertebrate (a mosquito bite on my own calf that swelled excessively).

Though this listing belies it, our walk did not start out auspiciously. After the initial web excitement, we headed down a block that looked terrifically dull. Desultory, underwatered sycamore and London plane trees lined the edge of a tired concrete path. Nothing moved; the afternoon was hushed. We were alone on the street, with not even a bored, idle squirrel for company. But Eiseman beelined to the trees and flipped over a leaf.

“This jumped out at me,” he said as I followed him, vexed. What
this
was was not obvious. He twisted a leaf between his fingers just overhead. I looked up at it: it looked vaguely unhealthy. Then my eyes adjusted, as if coming into a cool, dark room after a summer’s afternoon outside. Suddenly I looked
through
the leaf—and
that was when I began to see what he meant. The green tissue was peppered with black and yellow spots, “the characteristic feeding signs of the sycamore lace bugs,” Eiseman explained. “They don’t make holes; they just suck the green juice out and make it turn yellow.” These lace bugs lived on the underside of the leaf, which, on close examination, was splattered with their excrement—those black spots. Nearly indistinguishable from the excrement was a bevy of nymphs. “They are very beautiful bugs,” he said, pulling down the leaf for my examination, and in the process, raining little nymphs and young adult lace bugs all over his hair and shirt. If I squinted, and suspended disbelief, the adults were indeed almost pretty, their transparent wings crisscrossed with raised and darkened veins.

I considered these little guys while Eiseman regaled me with lace-bug trivia. The bugs are specialists, often preferring just one tree: there are sycamore lace bugs, birch tree lace bugs, and oak lace bugs. They are what is called, sweetly,
true bugs
: of the large order
Hemiptera,
which includes all sorts of bugs that do not have chewing mouthparts. Instead, the lace bugs have beaks, and invent creative ways of getting out of eggs. The oak-tree varietal grows up in tiny flip-top egg lids that pop open when they are ready to hatch.

As we moved on, I pointed out the young adult bugs now speckling him. He did a perfunctory brush at his hair and smiled: “It doesn’t matter.” For the rest of the walk a few lace bugs cruised happily on Eiseman’s chest.

As we headed down the sidewalk, every new species of plant we came across became an opportunity: an opportunity for new evidence of an insect. In an ordinary tree pit encircling its featured tree, a few plants at its base, and tree detritus (fallen leaves, twigs, seeds or nuts or seedpod), there might be thousands of bugs and spiders and other things to munch on the bugs or spiders. Soon I
was a co-participant in what seemed to be the major investigative strategy of the Searcher for Invertebrate Sign: flipping things over.
Flipping-Over
behavior marked Eiseman’s approach to most things, “if things aren’t jumping out at you,” he said (and hopefully they’re not). Eiseman was continually turning over leaves, which were often his first approach to a tree. “If you’re looking for an insect specific to a tree,” he suggested, “the leaves are the place to look.” Sure enough, nearly every single tree we passed bore the sign of some bug.
Holes
were rife. Just as the beginning arborist begins to use a leaf to identify a tree, it is soon clear that the
holes
of a leaf can be used to identify the hole-
maker
. In the motley array of trees, tree-pit plants, and wild weeds growing roadside and between sidewalk squares on our walk, we saw a dozen different kinds of leaf holes. Apart from the tortoise beetle and shothole leafminer holes, we saw large ragged holes like those a katydid or grasshopper might leave; punctuative holes that mimicked commas and semicolons; and birch leaves with neat, hole-punch circles, the sign of the aptly named leaf-cutter bee. The bee builds its nest elsewhere, but mines the leaves to make cylindrical cells for her eggs.

Other leaves were intact but unusually shiny. A resolute shiny streak indicated that a slug had been sliming along the leaf overnight. A slap-dash shining job was probably a wash of “honeydew,” the clear excrement of aphids, which itself draws other bugs and birds to feed on the sticky stuff. Holes and slime are only the beginning. A single leaf, nonchalantly fanning itself in the breeze, might be the repository of one of dozens of types of sign.

“Here’s something,” Eiseman said—and repeated on our walk together. There was always something. In this case, it was a browned, curving scribble on a leaf. “This is a leaf mine of a fly larva,” he explained, ending with a period. He must have sensed that I thought at least ellipses were due, and elaborated: “The fly inserted its egg there”—he pointed at the base of the trail—“and
the larva is living between the epidermal layers, and is munching along and making a wider trail as it grows bigger.”

My mind boggled a small boggle. The strip of denuded leaf we were looking at was a path cleared by a young fly who was growing up sufficiently quickly that the path he left in his wake had widened over the course of his living on that one leaf.

These leaf mines, I learned, are left mostly by moths, beetles, and flies, whose larva create a visible trail as they plow along, chomping leaf tissue. They spend their whole larval life in one leaf and then emerge as an adult. Many of the mines are very particular to the species of insect: the female always inserts her egg in a particular place, such as at the leaf’s edge or base. As a result, by looking at the starting point of the mine one can (if one knows quite a bit about insects) determine the larval species that is living there. The
type
of trail is species-specific, too. Some leave serpentine trails that draw an inscrutable image along the canvas of the leaf. Other mines cruise along the veins of the leaf. Still others are more blotch than trail, growing pools of ungreen leaf. We saw mines that followed a serpentine course and ones that hugged the leaf ’s perimeter: leaf-as-jogging-track.

It is not mines but
galls
that are the crowd-pleasers of the insect-track-and-sign world. “Some of the galls are what draw people in first,” Eiseman said with a straight face. This was initially hard to believe. A gall is a growth, a plant tumor, caused by a critter burrowing into the tissue of the plant when it is developing. The small lump, fold, or pouch that results serves as shelter and often food for the nymphs that the midge, sawfly, moth, aphid, wasp, or mite (not technically an insect) lay in it. To my eye, many galls looked a bit cancerous, the leaf blighted or with an embarrassing skin condition.

“How do the plants endure all this?” I wondered aloud. “Most of it seems so destructive.”

“Being deciduous helps: they get to refresh their leaves every year. Galls are a sort of agreement that’s been worked out, concentrating the damage to one spot. It gives the insect shelter and food.”

“The tree doesn’t get anything.”

“It gets less damage.”

Most galls do no serious harm to their tree hosts. Some galls are almost picturesque—and adorably named. I could imagine trying to hunt for the fuzzy red “hedgehog” gall; the flamboyant “sea urchin” gall, boldly pink and spiky; or the “wool sower gall,” a soft dotted pom-pom that reaches outward like a flower.

Each of these winsome galls actually holds tiny wasp larvae that reside on oak trees. If your city has oaks, you could find galls down the street. When I returned to New York City, I was barely out of the train before I come across an oak and quickly found a gall, green and pealike, on a leaf.

I started to wonder about wasp aesthetics: their galls are architectural beauties. If not inspiration for humans, there is a theory that galls might have served as a sort of inspiration for trees. As Eiseman described it, the theory suggests that galls kick-started trees into bearing us the fleshy fruits we now cultivate greedily, such as peaches and plums. If that were the case, fruits are really just evolutionary extensions of galls, developing because of wasps laying their eggs in the plant’s flowers, eventually altering the plant’s genome to produce galls that become bigger and more nutritious over time.

Galls are also a very particular sign: gall insects usually choose a specific place to induce a gall, as at the midrib, edge, or underside of a leaf. Most are on leaves, but some insects choose branches, twigs, or even flowers. You can open one up to reveal the tightly packed, sleeping larval species inside—or you can just infer the species from the shape and location of the nub.

 • • • 

Surprisingly, those leaves that have no sign, no holes, no smattering of excrement, are themselves sign of something else. They indicate that the tree is probably not from around here. Although some bugs are generalists, knocking about in our faces or homes or wherever they can find nourishment, many are extremely plant-specific. They might be born, grow, eat, mate, and die on the same plant. One type of plant—or even one individual plant—may be their entire universe. Plants native to North America have their own community of North American bugs that have evolved to live on and with the plant. However, non-native—what are increasingly called invasive
¹
—plants are often new enough to the area that no native bug has yet evolved to specialize in them. As a result, the invasive plants do not need to put any of their resources into defense chemicals or strategies; they can put all their energy into growing and reproducing. That is why invasive plants invade so well: they can spread quickly while native plants, struggling against the bugs, are lucky to maintain their numbers.

You can, thus, make a reasonable guess as to whether a tree is native by checking out its insect population. Walking by the lovely Norway maples, five-fingered leaves robust and hole-free, I suddenly realized that the “Norway” was not a rhetorical turn. The tree I was accustomed to seeing throughout New York City is an immigrant. Even the city Parks Department logo is a silhouette of what is probably a maple (or London plane, another non-native tree) leaf. The trees we passed looked gorgeous, each leaf custom-printed, dry-cleaned, and pressed. And largely sign-free.

 • • • 

Though Eiseman had not given any urban insect-sign tours, I was starting to think there may be a call for them. One might imagine that a typical city does not host too many bugs (outside of cockroaches and bedbugs); this walk was convincing me otherwise. Eiseman flipped over a stone and rocked a log with the toe of his shoe, causing shiny dark bugs to move quickly under the nearest leaf litter. In some ways, he suggested, cities are not
un
natural so much as they are
concentrated
nature. On his cross-country tour, highway rest areas turned out to be gold mines for bug-tracking. “It almost seems like in someplace like that, where there is just a little scrap of nature, life is more condensed.” Upon entering Texas, they discovered the Texas leaf-cutter ant at the parking lot where they had pulled over for a pit stop. Then, on going into national parkland, “we barely saw anything,” he said. The density of insect life was not the same, or maybe the method of exploring—wandering along waiting for something to pop up, rather than poking into every crevice at the rest area—is not conducive to finding sign.

Certainly if a rest area provides opportunity to find sign of insect life, a city must. Eiseman cataloged some urban elements that lead to good insect-sign hunting—beginning with the city’s tendency to never shut down. When Wabash, Indiana, was the first town to light itself up at night with electric light, onlookers were flabbergasted: when the lights went on, “people stood overwhelmed with awe,” the local paper reported. “Men fell on their knees, groans were uttered at the sight, and many were dumb with amazement.” We have grown accustomed to the ordinariness of nighttime lighting, but many insects are still in its thrall. Lit all the time, cities attract insects whose compound eyes are specially tuned to the short wavelengths of UV light, found in incandescent lamps and many fluorescent lamps. City streetlights are now usually a more energy-efficient sort, such as high-pressure
sodium vapor lamps, which emit less UV light but are still a siren call for various fliers. Insects use these light waves to find and choose mates, navigate, hunt, even migrate. So they must get very excited to find UV radiating toward them at every address and along every street. The UV-seekers include moths, of course, but also beetles, lacewings, things lacewings eat (aphids), various flies (caddis-, crane-, hover-, true-, scorpion-, damsel-, dragon-, even butter-), and wasps. About a third of them will perish in their excitement to touch the light. They hit the hot light, circle around it until exhausted, or make enough of a ruckus that a predator (bird or bat or other insect) gobbles them up.