Woolly bear caterpillars, the larval stage of the Isabella tiger moth (Pyrrharctia isabella), are a familiar sight in North America, especially during the fall season. These fuzzy caterpillars are popular for educational projects and are relatively easy to care for. This article will explore the diet of these caterpillars, their habitat, and how to care for them as they transform into moths.
Introduction to the Isabella Tiger Moth and its Caterpillar
The Isabella tiger moth belongs to the Arctiidae family, which includes approximately 11,000 species worldwide. The adult moth features bright colors such as scarlet, yellow, orange, and white, with hues ranging from black to beige. The larvae, known as woolly bear caterpillars or woolly worms, are equally striking, often displaying a burnt orange color in the middle with black ends. These caterpillars have thirteen segments and three sets of legs.
Habitat and Care for Woolly Bear Caterpillars
To properly care for a woolly bear caterpillar, it is essential to create a suitable habitat. According to entomologist Dr. Samuel Ramsey, a researcher with the United States Department of Agriculture, the following steps can be taken:
- Container: Place the woolly bear caterpillar in a clear glass or plastic container, such as a mason jar, or a cardboard box. Ensure the container has air holes or a mesh lid to prevent the caterpillar from escaping. It is advisable to keep only 1 to 2 woolly bear caterpillars in the same container at a time to avoid overcrowding.
- Habitat Enrichment: Cover the bottom of the container with leaves and plant debris to mimic the caterpillar’s natural environment. Adding twigs and leaves provides places for the woolly bear to hide, sleep, and eventually hibernate and build a cocoon.
- Cleanliness: Regularly check the container for droppings (frass) and clean it as needed. Use a twig or leaf to gently move the caterpillar to a different jar while cleaning the original container with a tissue or paper towel.
- Temperature Regulation: Woolly bear caterpillars need to experience outside temperatures to know when to hibernate and build a cocoon. Therefore, the container should be kept outdoors.
Dietary Preferences of Woolly Bear Caterpillars
Woolly bear caterpillars are herbivores with a broad diet. They tend to prefer low-growing, seed-bearing plants. Here are some of their favorite foods:
- Dandelions
- Plantain weeds
- Dock
- Burdock
- Aster
- Nettle
- Goldenrod
- Clover
- Sunflowers
- Lambs quarters
- Violets
- Yellow dock
- Curly dock
- Many native plants
If the preferred food sources are unavailable, woolly bears will also consume grasses and grains, including wild grasses, corn, and barley. Although they typically stay on the ground, they can sometimes be found in deciduous trees feeding on foliage such as maple and birch leaves.
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Dr. Ramsey notes that caterpillars have taste buds, and many will only eat certain kinds of leaves. Therefore, providing the right types of leaves is crucial. Dandelion leaves are a particularly popular choice.
Ensuring a Constant Food Supply
Woolly bear caterpillars need a constant supply of food until they hibernate and build their cocoon. It is important to provide them with a fresh supply of leaves, weeds, and grasses each day.
Hydration
Woolly bear caterpillars primarily get their water from plants. While they do not need a water container, small droplets of water can help them stay hydrated. Misting the inside of the container with water every day is a good practice.
The Life Cycle of the Isabella Tiger Moth
The Isabella tiger moth has a complete life cycle with four stages: egg, larva, pupa, and adult.
- Egg: Eggs are laid in clusters on the leaves of host plants.
- Larva (Caterpillar): The banded woolly bear larva emerges from the egg in the fall. Larvae go through several instars before they pupate. They actively disperse and may be seen moving in groups over turf, roads, and sidewalks.
- Pupa (Cocoon): In the fall, woolly bear caterpillars seek shelter under leaves, twigs, and logs to stay warm. They prepare for winter by going into hibernation, during which they may wake up occasionally to eat. In the spring, the caterpillar will rest on leaves or a branch and begin to spin a cocoon around itself, forming a pupa.
- Adult (Moth): After 1 to 3 weeks in the cocoon, a tiger moth will emerge. Adult Isabella tiger moths usually rest with their wings held rooflike over their bodies or flat out to the sides. The forewings are yellow or tan, pointed, and often have faint lines and small dark spots. Hindwings are lighter, with orange coloration more common in females.
Once the woolly bear caterpillar transforms into a tiger moth, it is best to release it into the wild. The moth can be observed for a few hours after it emerges, but ultimately, it belongs in its natural habitat.
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Overwintering and Hibernation
Woolly bear caterpillars overwinter as larvae. They prepare for the cold by finding a place to spend the winter, often under logs, boulders, boards, rocks, or other dark places. The caterpillar produces a natural organic antifreeze that protects the interior of its cells, allowing it to survive freezing temperatures as low as -90 degrees Fahrenheit. During hibernation, most of the caterpillar’s mass freezes solid, including its heart, gut, and blood. This freezing occurs outside the body cells, preventing cellular damage.
According to Greg Stack, University of Illinois Extension Educator in Horticulture, it is essential to provide the caterpillar with a cold environment for it to transform into a moth. If keeping a woolly bear caterpillar in a cage, the cage should be covered with a metal screen instead of fabric netting to protect it from rodents. The cage should be buried in the ground next to the foundation of the house and covered with leaf litter during the cold months, typically from late fall to late April or mid-May.
Folklore and the Woolly Bear Caterpillar
The woolly bear caterpillar is also known for its supposed ability to predict the severity of the coming winter. According to folklore, the length of the black bands on the caterpillar indicates the harshness of the winter. A wider brown band suggests a mild winter, while a narrow brown band indicates a severe winter. Some variations of this belief suggest that the color of the stripes or the direction in which the caterpillar crawls can also predict the winter weather.
Several towns and festivals celebrate the woolly bear caterpillar. Banner Elk, North Carolina, hosts a Woolly Worm Festival that features crafts, food, and races. Other towns, such as Vermilion, Ohio, and Beattyville, Kentucky, also have annual Woolly Worm Festivals.
Distribution and Abundance
Banded woolly bears are common across the United States, Mexico, and Southern Canada. Their abundance, wide distribution, and flexible diet make them an ideal choice for a home school science project. They can be found crawling across lawns, fields, pastures, and prairies, as well as seeking shelter under dead plant debris.
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There are typically two generations of woolly bears each year. The first hatches in May, eats during the summer, and transforms into moths in the fall. The second generation hatches in the fall, eats a little, hibernates over winter, eats more in the spring, and then turns into moths.