Several species of black and yellow caterpillar live on trees in the United States. Most of them are not poisonous to people or pets. However, at least one variety of black and yellow tree caterpillar requires handling with care because of its irritating hairs. Two other species that live on plants near the ground contain small amounts of a heart poison that could harm some people and small animals.
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The yellowneck caterpillar, or Datana ministra, is a nonpoisonous species found across the United States. At maturity, the yellowneck has a 2-inch black body with yellow stripes running its full length, as well as a yellow neck. Though the yellowneck caterpillar won’t harm people or pets who ingest or touch it, the insect can damage trees. The yellowneck is partial to oaks, elms and hickories, and colonies of hundreds of caterpillars can defoliate a young tree in one summer. Control yellownecks by cutting off and destroying infested tree branches. Insecticides containing the toxic bacteria Bacillus thuringiensis can quell yellowneck outbreaks if you apply the compounds when caterpillars emerge in mid-summer.
This close relative of the yellowneck caterpillar lives west of the Rocky Mountains, where it feasts on azalea trees, oaks and apple trees. The azalea caterpillar’s black body grows to 2 inches, with eight broken yellow and white stripes from front to back. Its head, neck and legs are bright red. Azalea caterpillars reach peak activity in late summer and early fall. They’re harmless to people and animals. Controls include the pesticide Sevin Dust, as well as insecticides containing Bacillus thuringiensis, malathion or cyfluthrin.
Catalpa Sphinx Caterpillar
Elm, catalpa and apple trees are favorites of the catalpa sphinx caterpillar, or Ceratomia catalpae, a hornworm species that grows a black spike on the end of its body. The catalpa sphinx grows to 3 inches, and has a black body with pale yellow stripes running the length of its sides. Catalpa sphinx caterpillars are not poisonous to people or pets, though they can strip trees of their leaves. The caterpillars, also called Catawba worms, are bred commercially on catalpa farms and used as fish bait. Control them manually, by picking them out of trees and stepping on them.
Spotted Tussock Caterpillar
The spotted tussock caterpillar’s signature trait is its hair, which covers its body in black and yellow bands. Longer, white hairs protrude from the caterpillar’s front and back. It’s tempting to pick up the fuzzy spotted tussock, or Lophocampa maculata, but its hairs can irritate the skin in people with allergies. The spotted tussock grows to 1.5 inches and lives in warmer climates in the United States, including in the South and California. You’ll find it feasting on poplars, maples and oaks, but its numbers are not high enough to cause serious harm to trees. Environmental controls are unnecessary.
Two varieties of black and yellow caterpillars contain cardenolides, or poisonous alkaloids related to the heart stimulant digitalis. They don’t live in trees, but if you’re watching out for potentially toxic caterpillars, you should know about the Monarch caterpillar, or Danaus plexippus, and the Cinnabar moth caterpillar, or Tyria Jacobaeae. The Monarch caterpillar grows to 2 inches and has black, yellow and white stripes running horizontally across its body. The Monarch feeds exclusively on milkweed, a ground-dwelling vine that contains cardenolides. Cinnabar moth caterpillars grow to about 1 inch, and have black and yellow horizontal stripes. They feed on the tansy ragwort, which also contains cardenolides. Both caterpillars store cardenolides in their bodies. A human would have to consume large numbers of these caterpillars to develop heart trouble, but many animals, including birds and rodents, are more vulnerable to poisoning from cardenolides because they are small.