Signs of Leaf Eaters – Background

You don’t have to go far to see nature at work – bees visiting flowers, fireflies twinkling in a field, a hawk circling overhead. Less familiar, but right under our noses, are countless tiny animals busily feeding upon leaves or hiding in them from their predators. The signs of leaf-eaters, or leaf-hiders, are easy to find. Peer into any bush or tree and you are sure to see leaves that are chewed, rolled, folded, or sewn up with silk. Snails, aphids, and caterpillars feed upon this bountiful food supply, while spiders and hunting insects prowl amidst the leaves. Looking for signs of leaf-eaters gives us a glimpse of an ecosystem in action.

The place where a plant or an animal lives is its habitat, where it has what it needs to survive – sun and soil, food and water, shelter from the weather and predators, a place to raise young or for seeds to grow. A bullfrog’s habitat is a pond, a squirrel lives in the forest, a sunny field is habitat for grasses, goldenrod, and meadow voles. Every organism is part of the ecosystem in its habitat. Ecosystem, short for “ecological system,” means all the plants and animals in a place, their connections with each other and with the non-living parts of their environment – the sun, air, water, rocks, and soil. In an ecosystem, plants and animals are linked in food webs, rocks and organic debris slowly turn into soil, rainfall brings water and streams carry it away, the sun warms the air and provides energy for plants to grow.

How is the sun’s energy harnessed in an ecosystem? Nature’s own solar collectors, the leaves of plants, capture sunlight and use it to make sugars and starches – the building blocks of stems, fruits, seeds, and other plant parts. Plants are called producers because they can make food, while animals are consumers since they must eat plants or other animals. Those animals that feed on plants, like deer and rabbits and all the tiny leaf-eaters, are called herbivores. Those that eat other animals, like bobcats and praying mantises, are called carnivores. In every ecosystem, energy is transferred along food chains – from sun to plant to herbivore to carnivore. Some animals are very specialized, eating only one kind of plant or prey, but most animals eat a variety of foods, and so they are a part of many different food chains, interconnected in an intricate food web. A change in one part of the ecosystem can have an effect throughout, because of these many interconnections. Learning about the food web in a place is a key part of understanding how the ecosystem works.

Fueled by the sun, plants are the basis of every food web, directly or indirectly providing nourishment for everything that walks, crawls, or flies. From the moment they first appear in the spring, a plant’s leaves come under attack by a host of leaf-eaters. In fact, by late summer, it’s hard to find a leaf that’s still intact. The patterns of leaf damage can often give us clues about what kind of leaf-eater has been at work. Leaves with discolored areas – patches that are pale or dark, mottled or browned – show where insects with sucking mouthparts, like lace bugs, plant bugs, leafhoppers, or aphids, have pierced them and drawn out the juices. Other patterns are made by insects with chewing mouthparts. Scalloped edges on leaves are often the work of caterpillars. They tend to move their heads through an arc as they take bites, creating a connected series of curves in the leaf’s edge. Jagged edges show where grasshoppers or katydids have chewed. Some leaves have lacy patches where tiny moth larvae or Japanese beetles have eaten away the softest tissues, leaving the leaf’s fine network of veins intact. These insects are called “skeletonizers” because they leave only the skeleton of the leaf behind.

Another pattern to look for is leaf mining, made by insects that feed between the layers of the leaf. The adult insect pierces the outer surface with her egg-depositing tube (ovipositor) and lays the eggs underneath. The larvae eat the soft inner tissues, chewing away broad areas that look like windows or winding tunnels that look like roads on a map. Often the tunnel contains a dark line – the insect’s droppings left behind as it eats its way through the leaf’s tissues.

There seems to be no end to the creative use of the leaf in the animal world. Folded, rolled, and silk-covered leaves may be signs of feeding or shelter construction or both. Many kinds of spiders hide inside a folded or rolled leaf while waiting for their prey, and others build a leaf-walled nest for their young. Fall webworm and ugly nest caterpillars work with their siblings to wrap whole branches in a silky net within which they feed upon leaves in safety.

Many kinds of moths, butterflies, and sawflies roll, fold, or tie leaves together and then hide inside these shelters while feeding on the leaf tissues. A common leaf-folder is the larva of the maple trumpet skeletonizer moth. This caterpillar uses silk strands to fold the leaf and then feeds on the leaf from within this shelter. It constructs a tube around itself out of its droppings, and as it grows, the tube bells out into a trumpet shape to accommodate its extra girth.

Holes of all shapes and sizes are common signs of leaf-eaters, but some holes have a different origin. The maple leafcutter moth lays its eggs on young maple leaves as they emerge in springtime. Hatching out of the egg, a tiny larva begins its life by cutting out a round piece of leaf that it pulls over its body like a tent and fastens down with silk. It feeds by poking its head out and eating from the leaf, leaving a circle of tiny holes all around its shelter. As it grows, it adds another leaf piece, sewing the two together to make a case like a turtle’s shell. In its leafy cover it hides from predators like warblers and chickadees on the hunt for a tasty morsel. When ready to pupate, the larva, case and all, floats to the ground, where it spins a cocoon in the leaf litter. The next spring, the adult moth emerges and lays its eggs on a newly formed maple leaf. The leafcutter moth lives most of its life on a single maple leaf. The leaf is its habitat, providing food, water, shelter, and a place to rear its young. The moth performs its role in the ecosystem by eating leaves, producing young, perhaps providing food for a predator, and eventually becoming nutrients in the soil from which a new maple tree may grow.

On a late summer day, fields, forests, gardens, and schoolyards are busy places, filled with the buzzing and stirring of insects and other small creatures. In all these places, wild and tame, we are sure to find signs of an ecosystem in action, especially if we look closely and learn to read the stories written in the leaves.

Suggested Reading

Eastman, John. The Book of Field and Roadside: Open-Country Weeds, Trees, and Wildflowers of Eastern North America. Mechanicsburg, PA: Stackpole, 2003.

Eiseman, Charley and Noah Charney. Tracks and Sign of Insects and Other Invertebrates. Mechanicsburg, PA:  Stackpole Books, 2010.

Pfeiffer, Bryan. Maple Leafcutter and Its Turtle-like Existence. Northern Woodlands, September 2009.  http//northernwoodlands.org/site/maple_leafcutter_and_its_turtle-like_existence.

Stokes, Donald. A Guide to Observing Insect Lives. Boston: Little, Brown, 1983.

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