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14 Caterpillars on Oak Trees: Identification Guide

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The forest tent caterpillar, one of many oak-eating species in this guide

The forest tent caterpillar, one of many oak-eating species in this guide

What's Eating Your Oak Trees?

This is a quick and easy guide to the caterpillars that you are likely to find on oak trees. These species use oak leaves as a food source and can sometimes be so numerous that they defoliate and kill an entire tree. This is unusual, however: most caterpillars that eat oak leaves will only brunch on a few branches worth in an entire lifetime.

If you do find caterpillars on your oaks, it's important to realize that they are part of a grand cycle of hosts, plants, caterpillars, and predators. While it does happen, it is very unusual for a caterpillar infestation to get so severe that it seriously damages one tree, let alone a whole forest.

This guide includes both pest species and less-common caterpillars that you will find on your oak trees.

For each oak-eating caterpillar species, this guide begins with The Basics:

  • What is the scientific name?
  • Where does this species occur?
  • Will it seriously damage plants or trees?
  • Does it sting or cause irritation?
  • Can it be controlled without pesticides?

We also include photos, descriptions, and natural history details that help you understand your oak-eating caterpillar a little bit better, so you can decide whether to go all-in on control or to live and let live by recognizing the critter's right to exist as part of Nature's plan.

Chart of Common Caterpillars on Oak Trees

SpeciesAppearanceReason for Concern?

Lymantria dispar [gypsy moth]

Spines/fur; rows of red and blue raised bumps

YES. Contact university/ag extension office if you find one.

Forest tent caterpillar

Blue/brown with bright cream spots along back

Can defoliate entire trees

Eastern tent caterpillar

Like forest tent, but has a line instead of spots

Sometimes a pest, if enough numbers are present

Fall cankerworm

Green "inchworm" that moves by looping its long thin body

Sometimes a pest

Oak leaf skeletonizer

Very small green caterpillar that eats between leaf veins

Not usually cause for concern but can sometimes injure trees

Variable oakleaf caterpillar

Variable; almost always has diamond-shaped marking on back

Not typically a serious concern

Orange-striped oakworm

Thin orange stripes on dark brown background

Not usually a serious concern

Red-humped oakworm

Bright red hump or ball on both ends

Can occur in numbers but nor usually a concern

Tussock moths

Brightly marked with tufts of light-colored fur

Can injure trees if there are enough of them

Genus Catocala

Gray or brown, flattened, blends in with twigs and bark

Not a concern

Polyphemus moth

Big green caterpillar with small red and silver markings

Not a concern

Buck moth

Reddish-brown; spines; occurs in groups; STINGS

Not a concern but this species can sting

California oakworm

Medium-sized brown caterpillar

Can injure trees if there are enough of them

Lymantria dispar [Gypsy Moth]

Lymantria dispar [Gypsy Moth]

1. Lymantria dispar (Spongy Moth)

The Basics:

  • What is the scientific name? Lymantria dispar
  • Where does this species occur? Across the US
  • Will it seriously damage plants or trees? Yes, it can be a very serious best
  • Does it sting or cause irritation? The fur can irritate skin
  • Can it be controlled without pesticides? Very difficult, with or without pesticides

Although its common name has fallen out of favor due to the negative association it brings to the Romani people, this species remains one of the best-known and most-feared of all oak tree caterpillar pests. While most oak-eating species will eat a few branches worth of leaves in a lifetime, these caterpillars attack in huge numbers and can defoliate entire swathes of forest.

If you find one of these caterpillars, it is very important that you contact a nearby University or Museum and speak to someone who can identify your find for you. Scientists, arborists, and other professionals who care for forests are always on the lookout for this species.

To identify this caterpillar, look for two rows of red and blue bumps on the back. Immature caterpillars have two tufts of fur on either side of their head that look a little like ears. Adult female moths are cream-colored and stay on the tree trunk where they hatched from the cocoon; males fly in the daytime and may be mistaken for brown butterflies.

Forest Tent Caterpillar

Forest Tent Caterpillar

2. Forest Tent Caterpillar

The Basics:

  • What is the scientific name? Malacosoma disstria
  • Where does this species occur? Across the eastern US
  • Will it seriously damage plants or trees? Yes
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes but difficult

The forest tent caterpillar is attractive, common, and often seen as it crawls along the forest floor. The problem with this species is that it occasionally shows up in huge numbers, and when that happens, it can cause destruction that rivals Lymantria dispar. I have walked in an oak forest under attack by forest tent caterpillars, and I could literally hear them eating—millions of tiny jaws chomping on oak leaves. Their poops pattered down like rain.

Although a severe attack is a cause for serious alarm, most of the time, these caterpillars are simply one of many occurring on a host tree, and they don't generally cause much trouble. The adult moth is a lovely faun-brown color, with a stout, furry body.

3. Eastern Tent Caterpillar

The Basics:

  • What is the scientific name? Malacosoma americanum
  • Where does this species occur? Across the eastern US
  • Will it seriously damage plants or trees? Yes, it can
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes, but with difficulty

This tent caterpillar, like the previous species, forms mats or "tents" where the caterpillars all rest between meals; they also shed their skins in the tent. This shelter is distinctive, but there are other species, some not closely related, that also make webbed shelters where the caterpillars live communally.

This oak-eating caterpillar can cause damage when it shows up in numbers, but it's not typically as big of a problem as the last two species. It resembles the eastern tent caterpillar but has a line down the back instead of cream-colored spots; the adult moths are similar.

4. Fall Cankerworm

The Basics:

  • What is the scientific name? Alsophila pometaria
  • Where does this species occur? Across the US
  • Will it seriously damage plants or trees? Yes, it is a local pest of oaks and other trees
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes

The fall cankerworm is a species of inchworm, which means it's in the family Geometridae. This is a very large family that includes all of the inchworms and more. Inchworms like the fall cankerworm get their nickname from the distinctive way that they move: they stretch their long, thin body forward, grab on with their front legs, and bring the hind end of their body up to meet the front legs, making a loop of their body (other, unrelated caterpillars called "loopers" also use this form of locomotion). Old-timey entomologists saw this and called them inchworms for the way it looked like they were "measuring the marigolds," as the song goes.

The adult male moth has broad, pale gray wings; the female is wingless and never leaves the vicinity of the cocoon.

Oak Leaf Skeletonizer showing leaf damage

Oak Leaf Skeletonizer showing leaf damage

5. Oak Leaf Skeletonizer

The Basics:

  • What is the scientific name? Bucculatrix ainsliella
  • Where does this species occur? Much of North America, including Canada
  • Will it seriously damage plants or trees? Yes
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes; biological controls like parasitic wasps have been effective

This small moth lays eggs near the veins of oak leaves. The immature caterpillars start life as leaf miners, which means they burrow inside the leaves; as they grow, they move to the surface of the leaf and feed there, eventually eating everything between the veins. This "skeletonizing" behavior is the source of the insect's common name.

Variable Oakleaf Caterpillar

Variable Oakleaf Caterpillar

6. Variable Oakleaf Caterpillar

The Basics:

  • What is the scientific name? Lochmaeus manteo
  • Where does this species occur? Northern US with related species across North America
  • Will it seriously damage plants or trees? Not usually
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Not usually necessary

Variable oak leaf caterpillars are part of a very large group of moth species commonly called "prominents." The caterpillars can be very strange in appearance, and they often take on many different colors or forms; the variable oak leaf caterpillar is one of the more shape-shifting examples of this group.

The adult moth is usually more or less plain brown or gray, with a very furry body. This species will not usually do too much damage to oak trees.

Orange-Striped Oakworm

Orange-Striped Oakworm

7. Orange-Striped Oakworm

The Basics:

  • What is the scientific name? Anisota senatoria
  • Where does this species occur? Eastern US
  • Will it seriously damage plants or trees? Not usually
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Not usually necessary

Sometimes in late summer, numbers of these caterpillars will suddenly appear, seemingly out of nowhere. You will see them crawling along the ground near oak trees as they search for a place to burrow down and pupate before hatching out the following spring as adult moths.

They don't actually appear out of nowhere, of course—like many other caterpillar species, orange-striped oakworms spend their days high in the tree, feeding on leaves and trying not to get eaten themselves by a hungry bird. When it's time to pupate, the all move en masse down the trunk (some will just drop to the ground from where they're sitting) and spread out to find a place to dig. This is when you are most likely to find them.

This species does not typically do much damage to the host tree, although they will eat their share of leaves. The adult moth is sublimely beautiful.

8. Red-Humped Oakworm

The Basics:

  • What is the scientific name? Symmerista canicosta
  • Where does this species occur? Eastern US
  • Will it seriously damage plants or trees? Not usually, though they may occur in numbers and strip leaves from branches
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes, not usually necessary

The red-humped oakworm is aptly named. It eats oak leaves, for one thing, but it also has a striking red hump on one end and a shiny red head on the other. It belongs to the family Notodontidae, aka the "prominents," which includes some very strange-looking caterpillars (if you have a minute, search up the caterpillar of the Lobster Moth). Like many other prominents, these caterpillars like to feed in groups, and enough of them can seriously damage a young or sick tree.

The adult moth is a soft gray color with bright cream margins on the forewings.

Live Oak Tussock

Live Oak Tussock

9. Live Oak Tussock Moth

The Basics:

  • What is the scientific name? Orgyia detrita
  • Where does this species occur? In the western US, with closely related species across North America
  • Will it seriously damage plants or trees? Sometimes
  • Does it sting or cause irritation? Yes, for those with sensitive skin
  • Can it be controlled without pesticides? Yes, but not usually necessary

Tussock moths in the genus Orgyia occur throughout North America. They have a distinctive look, with a number of light-colored tufts or "tussocks" of fur on the back; one theory is that these tufts resemble the cocoons of parasitic wasps, which may deter a wasp from attacking the caterpillar because it appears to already be parasitized.

The white-marked tussock moth, O. leucostigma, is a very common pest of ornamental trees in cities and suburbs across the country.

caterpillars-on-oak-trees

10. Dagger Moths, Genus Acronicta

The Basics:

  • What is the scientific name? Various species in the genus Acronicta
  • Where does this species occur? Across the US and Europe
  • Will it seriously damage plants or trees? No
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Not necessary

This is a large group of similar-looking gray moths. Many of them feed on oak leaves, but I will mention a couple of them here because you may find one of them wandering around on the trunk of an oak tree as it looks for a place to make its cocoon. These caterpillars feed singly and will not typically cause damage to the tree.

Typical Underwing caterpillar

Typical Underwing caterpillar

11. Underwing Moths, Genus Catocala

The Basics:

  • What is the scientific name? Various species in the genus Catocala
  • Where does this species occur? Across the US
  • Will it seriously damage plants or trees? No
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Not necessary

Like the dagger moths (above), underwing moths tend to look alike and have many species that use oak leaves for food. While underwings may be confused for dagger moths while resting with their wings folded, once they fly, it becomes evident why Catocala moths are called "underwings"—their hind wings have brilliant red, orange, or yellow bands that flash when they fly. These colors are well-known in the insect world as warning coloration, and any predator suddenly seeing bright red or orange will assume that the prey they're chasing may be able to sting or fight back in some way. The moth is completely harmless, but its bluff may allow it time to escape.

The caterpillars are all very similar and blend in with the twigs and leaves of the host plant.

Polyphemus moth caterpillar

Polyphemus moth caterpillar

12. Polyphemus moth

The Basics:

  • What is the scientific name? Antheraea polyphemus
  • Where does this species occur? Eastern US
  • Will it seriously damage plants or trees? No
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Not necessary

This huge, gorgeous moth is one of the giant silk moths, family Saturniidae. The caterpillar is green, fat, and round, about the size of your thumb. It feeds singly on oak and several other trees, and if you're lucky, you may find one hanging out on a low branch near chewed-up leaves. The caterpillar leaves the food plant and spins a tough round cocoon on a nearby shrub or small tree, where you may find them in the winter once all the leaves have fallen.

The stinging caterpillar of the buck moth

The stinging caterpillar of the buck moth

13. Buck Moth

The Basics:

  • What is the scientific name? Hemilauca maia
  • Where does this species occur? Eastern US; similar species across the US
  • Will it seriously damage plants or trees? No
  • Does it sting or cause irritation? Yes; this species has venomous spines
  • Can it be controlled without pesticides? Not usually necessary

This is the only species on this list that can sting, and it can REALLY sting, comparable to a bee sting. The spines along the caterpillar's back are loaded with venom, and if you put your hand on one you will feel it for hours. Unfortunately, back moth caterpillars tend to travel and rest in large groups, often on the trunks of trees, so it's possible to accidentally brush up or lean against a whole lot of them at once. If this happens, you may need to make a trip to the emergency room, especially if you are allergic to bee stings!

On the plus side, adult buck moths are beautiful!

14. California Oakworm

The Basics:

  • What is the scientific name? Phryganidia californica
  • Where does this species occur? West Coast of US
  • Will it seriously damage plants or trees? Yes
  • Does it sting or cause irritation? No
  • Can it be controlled without pesticides? Yes

These small green caterpillars sometimes infest live oaks and can cause considerable damage. However, it is unusual for them to actually kill or seriously weaken the host tree. They are found only on the West Coast.

Sources

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.