White Woolly Bear Caterpillars - All About Them

White Woolly Bear Caterpillars – All About Them

Numerous hairy caterpillars appear in the fall but do not cause much damage during this time; some of these hairy friends are the white woolly bear caterpillars.

Hairy caterpillars are a curious sight that most people want to know what they are and if they are harmful in any way.   From a distance, the caterpillars can appear inviting.  They come with variable colours and tufts of hair protruding from their bodies.

The best advice to follow for any unknown insect is to avoid touching it or making any contact unless you are familiar with the species.

Identifying these hairy caterpillars in the fall is challenging.  They come in a range of colours from white to bright yellow, even within the same species. To be able to identify these caterpillars, you will require a prepared specimen with a microscope.

Here we will discuss the few common hairy caterpillars found in the fall.

Hickory Tussock Moth – (White Woolly Bear Caterpillars)

Also known as the white woolly caterpillars or white woolly worm, this worm is white with a black line down its back.  Some of them can be all white without the black line and are called albino woolly bear caterpillars.

Some appear to have tiny black spots instead of a black line; sometimes, the black line appears more like individual tufts than a line.  This worm also has four small areas with a very thin cluster of black hairs longer than the rest of the fuzz.  These are called pencils and are found on each corner of the body.

Hickory Tussock Moth - (White Woolly Bear Caterpillars)

Though not a true worm, the white woolly worm is found in the eastern U.S and Canada. The hickory tussock caterpillar has been reported to be poisonous, but the worst reaction is a skin rash if you touch one of the woollies.

Its favourite diet is oak, walnut, maple and ash leaves.  Just like their cousins, the yellow-spotted tussock caterpillar, the white woolly worm loves to live in clusters of longer bristles that stick out, in either black or white.

Banded Tussock Moth

Another late summer or early fall caterpillar is the banded tussock (Halysidota tessellaris), another hairy caterpillar.

Its larvae show variable colour patterns, but it is mostly yellow or white hairy bodies.  Its paired tufts of black and white bristles on the front and back and a tan to an orange horizontal line on its head telling it apart easily.

These caterpillars feed on leaves of multiple shrubs and deciduous trees and shrubs in Michigan.  They are easy to find on the upper surfaces of leaves.

This species has only one generation, with mature caterpillars coming as early as July in the southern parts of the Michigan state.

Woolly Worm Or Woolly Bear Caterpillars

The woolly worm or woolly bear (Pyrrharctia isabella) is popularly known for its weather prediction. It is the caterpillar that people tend to look for a weather forecast about the coming winter.   The traditional story followed by many today says that the narrower the rust-brown stripe, the harsher the winter.

Some caterpillars may lack the brown stripe due to genetic diversity.  Larvae are usually black, with the central brown stripe widening to a variable degree as the woolly bear grows into later life stages.

The woolly bear has 2 generations annually, but the fall one is most noticeable.  They will be all over looking for a protected location to spend winter.  They love to spend winter under leaves or other plant debris.

When spring comes, the insect thaws and life resumes as normal.   The woolly worms are about 2 inches long and have a diverse diet in the late summer and fall, consisting of grasses, leaves like birch or maple, flowers like clover, sunflowers and asters. Their damage is minimal and hardly recognized.

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American Dagger Moth

This caterpillar is either white or yellow, with five distinct tufts of long black hairs shooting from its body, attracting attention every fall.

The American dagger moth (Acronicta americana) loves to rest on the lower side of the leaves with its head curled over to one side. This behaviour differentiates them from the banded tussock moth caterpillar that rests on the upper leaf surface.

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They feed on various hardwood tree species and are commonly found in forests or among trees in the backyard, starting from August to October.  They are not known to cause economic damage to plants.

What To Do When You Encounter These Hairy Caterpillars

Now that we all know they appear in the fall, it’s best to avoid touching them by all means.  Some hairy caterpillars are known to have urticating hairs that penetrate the skin with ease.

These hairs can break off easily and puncture your skin, causing injury or irritation.  Remember, the hairs are microscopic and cannot be easily seen on your skin.

Some people experience severe allergic reactions after coming into contact with these worms.  The degree of severity depends on an individual human’s physiology.

The irritation they cause to humans is a natural defence mechanism against their predators.  Overall, do not touch these caterpillars, no matter how pretty they may look to you.

If you must touch them, put on a pair of gloves first before touching them.

What To Do When You Encounter These Hairy Caterpillars


Nature is beautiful!  And to see these white woolly bear caterpillars in various colours just confirms how breathtaking nature is.

Human interruption is what causes these and other important creatures to diminish on planet earth.

These worms pose no harm to anyone; they are just an addition to beautiful nature.  Nature know to introduce new things and when to exit the stage.  They love to hang around plants and trees of their liking with little to no interruption to humans.

We should treat them the same way – no interruption at all unless need be.  And even when the need arises, it’s best to handle them with care and allow them to enjoy this planet together with us.

Life would be so boring without these and other unique creatures. Make a better organic world for us all to live happily.    Enjoy your gardening journey!