Fat caterpillars, also known as woolly bear caterpillars, are the larval form of several moth species in the family Arctiidae. They are characterized by their plump, cylindrical bodies covered in long hairs or bristles. Some of the most common fat caterpillar species include the banded woolly bear, black woolly bear, and salt marsh caterpillar. These furry insects are popular among children and gardeners for their cute, fuzzy appearance. However, their voracious appetites can make them agricultural pests. Understanding the types of fat caterpillars, what they eat, and their life cycles can help manage their populations and appreciate their role in the ecosystem.
Common Types of Fat Caterpillars
There are hundreds of species of woolly bear caterpillars around the world. Some of the most widespread in North America include:
Banded Woolly Bear
Scientific Name: Pyrrharctia isabella
The banded woolly bear is the most well-known fat caterpillar in North America. It has alternating reddish-brown and black bands across its body. The wider the brown bands, the milder the coming winter is thought to be according to folklore. This species feeds on herbaceous plants like dandelions, asters, and grasses.
Black Woolly Bear
Scientific Name: Spilosoma virginica
As the name suggests, this species is solid black or dark gray. It feeds on a wide variety of plants, including lettuces, clovers, grasses, and woody plants. The black woolly bear is covered in long, fine hairs that can irritate human skin upon contact.
Salt Marsh Caterpillar
Scientific Name: Estigmene acrea
The salt marsh caterpillar is white or light yellow with distinct black spots and long black hairs arising from red-orange bases. It’s commonly found in coastal salt marshes where it feeds on grassy marsh plants. The hairs of the salt marsh caterpillar contain toxins that can irritate human skin.
What Do Fat Caterpillars Eat?
Fat caterpillars are voracious eaters during their larval stage, consuming leaves of trees, shrubs, and herbaceous plants. Some species are polyphagous, feeding on dozens of plant types, while others are more specialized.
Common host plants include:
– Grasses and cereal crops: wheat, oats, rye, barley
– Herbaceous plants: dandelions, clover, asters
– Garden plants: cabbage, broccoli, cauliflower, lettuce, spinach
– Ornamentals: dahlias, hollyhocks, cosmos, marigolds
– Trees: oak, birch, willow, apple, cherry
– Shrubs: blueberry, blackberry, raspberry
Fat caterpillars’ voracious appetites can damage crops and garden plants if populations are high. However, most only cause minor damage before transitioning to moths. Handpicking caterpillars may be necessary to limit impacts.
Fat Caterpillar Life Cycle
Fat caterpillars go through a complete metamorphosis with four life stages:
Egg – Eggs are laid on the undersides of leaves in clusters of 100 or more and hatch in about 10 days.
Larva – The caterpillar or larval stage lasts several weeks and goes through a series of molts. Caterpillars shed their exoskeletons as they grow.
Pupa – To pupate, the caterpillar creates a silk cocoon attached to a leaf or twig. Inside, the larva turns into a pupa.
Adult moth – After 1-2 weeks, an adult moth emerges from the cocoon. Most fat caterpillar moths are fairly drab-colored and fly at night.
Many species overwinter as larvae, sheltering under leaves or debris before emerging to feed ravenously in the spring. There is typically one generation per year.
Are Fat Caterpillars Harmful?
While fat caterpillars can damage plants and agricultural crops, they rarely cause major economic losses. Their stinging hairs can cause minor irritation in humans and predators, but they are not venomous or dangerously toxic. In fact, research shows the hairs may have medicinal benefits, like antibiotic properties. Overall, fat caterpillars play an important ecological role as pollinator food sources and nutrient recyclers. Their colorful fuzziness makes them fun insects for children and gardeners to observe. With basic monitoring, their plant damage can be minimized.
Conclusion
The plump, hairy larvae known as woolly bears or fat caterpillars belong to several moth species in the Arctiidae family. Some common types in North America are the banded, black, and salt marsh woolly bears. As larvae, these species feed voraciously on a wide variety of plants before pupating and transforming into moths. While their appetites can damage crops and garden plants, fat caterpillars rarely cause economic calamity. Their fascinating life cycles and fuzzy appearances make them popular among insect enthusiasts. With proper identification and monitoring, fat caterpillars can be appreciated for their important ecological roles and admired for their cute fuzziness wandering across the autumn landscape.
References
| Source | Reference |
|---|---|
| University of Wisconsin Master Gardener Program | Black Woollybear Caterpillar. (n.d.). https://wimastergardener.org/article/black-woollybear-caterpillar-spilosoma-virginica/ |
| Iowa State University | Salt Marsh Caterpillar. (2010). https://hortnews.extension.iastate.edu/2010/8-6/saltmarshcaterpillars.html |
| University of Maine | Brower, L.P. (n.d.). Woolly Bear Caterpillars. https://umaine.edu/news/blog/2011/09/21/woolly-bear-caterpillars/ |
| North Carolina State University | Banded Woollybear. (2013). https://content.ces.ncsu.edu/banded-woollybear |
