Woolly Bear Caterpillars: Good for the Garden?

Watch your step, especially if you spend the warm weather months barefoot.

You have a pretty good chance of seeing or perhaps squishing some fuzzy black caterpillars, sometimes known as “woolly bears,” as they inch their way slowly over roads, sidewalks, or even in your yard.

They’re dark, bristly, and common across the country. Here in Texas, you may have noticed saltmarsh caterpillars, which are found almost everywhere in the state. Eventually, they will transform into tiger moths, but before they do that, they are likely to get the attention of folks around for a lot of reasons. 

Woolly bears are fuzzy and you might think they’re kind of cute, especially if you’re a curious child, who might think of it as a possible pet. They move slowly, and they look soft.

Fortunately, the hairs on the caterpillar are not stingers, and you will not be hurt if you handle it. Nonetheless, if you are not absolutely sure what it is when you see it, it’s best not to touch it. 

Spring is their favorite time to come out of their hidey holes and start looking at the flowers and plants that are in full bloom, thinking about lunch.

During the winter hibernation period, the woolly bear will almost freeze solid. No matter how cold they get, they do not die because they cover themselves in glycerol, a type of natural antifreeze. 

In the spring, they thaw out and will become very active again. They will gorge themselves on food, gathering the energy they will need to create their cocoon and undergo their transformation into beautiful moths in a few months.

They love to eat low, herbaceous, and wild plants like dandelions, asters, goldenrod, birches, violets, maples, and certain grasses. The caterpillars have chewing mouth parts and when they are adults, they have siphoning mouths.  

As the temperatures rise, the woolly bear will feed like crazy, then begin preparing its cocoon. Once they are in their cocoon, they will begin to pupate, developing their adult parts, such as wings and antennae. After about a month, a tan or orange moth will emerge from the cocoon. They do not feed; they spend a few days mating and laying eggs, and then they die. The new eggs will hatch within about two weeks, and the process will start all over again. 

Predictor of weather?

There is a funny story that striped woolly bear caterpillars, which have black and orange stripes, will somehow predict the harshness of the upcoming winter. The legend goes that if the orange stripes are wide, it will be a longer winter, and if the caterpillar is a deep black, the winter will be harsher or colder. Just as with the groundhog story, there is no scientific evidence to support this, although it does add to Texas weather mythology and children enjoy the fun of it.  

Caterpillars are often a gardener’s nightmare, as they are voracious eaters and can quickly destroy a garden. But if you leave them alone, they can become beneficial pollinators, or become a source of food for certain birds.

Caterpillar poop is nutrient-rich and when mixed with fallen leaves and other natural debris, becomes food for worms, snails and other invertebrates who help turn the layers into a rich humus that enriches the soil. 

Anything you can do to encourage pollinators like bees and butterflies helps these woolly bears, too. Plant native wildflowers or create a butterfly garden in your backyard to support these insects.