Identifying Caterpillars in My Garden

Hungry Hungry Caterpillars!

September 3, 2019
A monarch is sitting with a caterpillar on a milkweed plant.
Cathy Keifer/Shutterstock

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As summer winds down the populations of caterpillars seems to be on the rise. Some are the larva of butterflies but most are moths. Let’s take a closer look and meet some interesting caterpillars in the garden.

All caterpillars have a similar lifecycle—egg, larva, pupa, adult. Caterpillars are near the bottom of the food chain, providing protein-rich nourishment to a multitude of birds, bees, bats, frogs, snakes, toads, and small mammals. There are about 11,000 species of moths in North America and many are important pollinators. The larvae of a few just eat dead leaves but most like the lush green ones better. If you are finding the leaves on some of your plants are suddenly being eaten, look closely for a caterpillar!

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We have had a bumper crop of monarch caterpillars on the milkweed this year and find chrysalises in the strangest places. The newly emerging butterflies are generally the only hint that a chrysalis has been hiding among the basil plants, attached to an eggplant leaf, or dangling from a plant support.

See my post on watching caterpillars turn from chrysalises to Monarchs!

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Like the monarch caterpillars, the larva of the milkweed tussock moth, also called the milkweed tiger moth, eats only milkweed which makes them poisonous to predators. It is a very hairy caterpillar that has some of the orange and black coloring that a monarch butterfly would have. The moth it turns into however is not brightly colored at all, just plain brown.

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The hornworms, which are sphinx moth larvae, have started popping up on the tomato and pepper plants. They are so well-camouflaged that I don’t usually notice them until a large amount of  foliage has disappeared. If you find one with white cocoons on its back, let it be. A braconid wasp has laid its eggs on the fat juicy caterpillar and when those larvae hatch they will eat the caterpillar from the inside out. Tiny braconid wasps are beneficial insects that you want to have living in your garden. 

See how to deal with tomato hornworms!

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The hairy, white hickory tussock caterpillar likes tree leaves, including hickory, oak, maple, and ash. This is one furry critter you don’t want to pet. It has barbed hairs that are toxic and can cause a nasty rash. After pupating it will turn into a brown and white moth.

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The dagger moth larva is another hairy white caterpillar to avoid touching. It has five long black spikes of hair sometimes called pencils - two pairs near the head and a single one at the rear and can cause a rash if handled. It eats tree leaves such as oak, maple, birch, and ash. After pupating it will emerge as a drab gray and white moth.

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The oddest caterpillar I have found so far this summer is the larva of the tiger swallowtail butterfly. It is smooth and green with blue dots. The googly eyes are fake, just there to scare away predators. It also has a stinky organ near the head called an osmeteria that it pops out to ward off threatening critters. It eats tree leaves also, cherry, apple, and ash being favorites.

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The fall webworms are back. They make their nests at the tips of the branches and feed only on the leaves within the nest. As they eat they expand the nest to include more leaves to chew on. Eventually a small nest becomes a huge ugly mass of crawling caterpillars and their droppings.They prefer apple, cherry, birch, oak, ash, and willow trees but lilacs, roses, and other ornamentals can also fall prey to their voracious munching. Since they feed for a month or more, a severe webworm infestation can easily defoliate a small tree. They overwinter in the soil as a pupa and emerge in late spring as a small white moth.

I am still on the lookout for a wooly bear caterpillar, the larvae of the isabella moth. They like to eat plantain and dandelions, no harm done there. The black and brown wooly bear has long been used to predict the harshness of the coming winter. According to folklore, the wider the brown band in the middle, the milder the winter will be. Read all about the Woolly Bear Caterpillar and Weather Prediction!

Interested in butterflies? Learn about butterfly gardening and plants that attract butterflies.

About This Blog

Get inspired by Robin Sweetser’s backyard gardening tips and tricks. Robin has been a contributor to The Old Farmer’s Almanac and the All-Seasons Garden Guide for many years. She and her partner Tom have a small greenhouse business and also sell plants, cut flowers, and vegetables at their local Farmer’s Market.

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