Many caterpillars have hairs or spines that are connected to poisonous glands, and in contact with human skin, they can cause pain, itching, burning, swelling, and blistering. Some caterpillars are venomous and possess sharp defensive spines that they use to defend themselves against predators. Here are some examples of poisonous and venomous caterpillars:

• Saddleback Caterpillar: A pale-green caterpillar about 3/4″ long.
• IO Moth Caterpillar: Pale green with yellow and red stripes. Often exceeds 2″ in length and is fairly stout-bodied. The nettling organs are borne on fleshy tubercles, and the spines are usually yellow with black tips. The spines are connected to poison glands. Ixora and rose are their favorite hosts.
• Hag Caterpillar: Light- to dark-brown with nine pairs (sometimes fewer) of variable-length, lateral processes, which bear the stinging hairs. It is found on various forest trees and ornamental shrubs.
• Puss Caterpillar: A convex, stout-bodied larva, almost 1″ long when mature, and completely covered with gray to brown hairs. Under the soft hairs are stiff spines that are attached to poison glands. When touched, these poisonous spines break off in the skin and cause severe pain. Most often found on oaks and citrus. In Florida, there are two generations a year, one in spring and the other in fall.
• Flannel Moth Caterpillar: This caterpillar is about 1″ long when mature. Stinging hairs are intermixed with soft hairs in diffuse tufts. Larvae are creamy white (Upper photo), turning dark as they mature (lower photo). They feed on oak and various other shrubs and trees.
• Assassin Caterpillar: This species of caterpillar is covered in many sharp, spiny structures called scoli. The tip of each spine is fragile and breaks off easily on contact, injecting the victim with the potent venom within. Though it takes anywhere from 20 to 100 stings to cause toxicity, each insect bears hundreds or thousands of brittle spines and can cause severe envenoming quite easily.
• Buck Moth Caterpillar: These harmful caterpillars have black bodies with distinct white spots. There is a light form of the species that has a body with a greenish coloring and more prominent spots that look like starfish. The head and limbs called prolegs are red. Multiple, thin, branching spines cover the body.

It is important to note that caterpillars are important parts of ecosystems and should be respected. If you must handle them for some reason, do so with caution and at your own risk.