Don’t touch that caterpillar

StoryImage( ‘/Images/Story//Auto-img-115273810624126.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘The poisonous spines on the saddleback caterpillar can cause a painful and debilitating reaction.’);

Many groups of animals have developed toxic venoms to assist in the procurement of food and for protection. Poisonous snakes and lizards come immediately to mind among the animals with backbones, but many fish and amphibians are also equipped with venom and an apparatus for dispensing it.

In the great group of animals known as the invertebrates (without backbones), we find the occurrence of venomous forms most frequently among the insects, ticks, and spiders of the phylum Arthropoda. Arthropod venoms, like that of other animals, are toxic substances probably not unlike bacterial toxins, about which we know comparatively little. Unlike many bacterial toxins that exhibit their effect only after an elapsed time after they have been introduced into the body, animal venoms require no period of incubation and take effect almost instantly.

Wasps, bees and spiders introduce their venoms into the body of an individual with special injection devices or poisonous jaws, and in some cases, the reaction of a human to the venom may be fatal. I have read and heard many times the statement that more people in the United States die each year from bee and wasp stings than do from the bites of venomous snakes. Of course, we all know that the bite of a black widow or brown recluse spider can lead to all sorts of unpleasant complications.

However, another group of venomous arthropods exists that can cause us pain and misery if we are unlucky enough to encounter them. In this instance we are referring to the so-called urticating (causing a painful, itching wheal) hairs and spines found on numerous species of caterpillars, which are the larval stages of butterflies and moths. As caterpillars are slow-moving creatures and a favorite of predators, it is not surprising that more than 50 different species of caterpillars have been reported as having developed urticating hairs and spines. The protective spine or hair is usually hollow and connected to a venom gland, which releases the stored toxin when the triggering mechanism is stimulated.

Of the many caterpillars in the U.S. that possess urticating spines and hairs, the saddleback, puss and the Io moth caterpillars are perhaps the most widespread and are of prime interest to us.

The saddleback is about an inch in length and has several large spines, on large projections and smaller ones, that stick out from the sides of the body. The “saddle” consists of an oval, purple spot in the middle of a green patch on the middle of the back. As the saddleback is an attractive caterpillar (as far as caterpillars can be attractive), they frequently pique the interest of children who may touch them. The venom of the saddle back causes a burning, painful sensation that may be as severe as the sting of a honeybee. The saddleback is a general feeder and may be found in association with shade trees and ornamental shrubs.

The puss caterpillar is about an inch in length and is broad and flat in shape. It is covered with long, silky hairs that are grey to reddish-brown in color. The hairs hide numerous shorter spines that discharge venom upon contact. The sting of the puss caterpillars is generally considered to be the most severe of the stinging caterpillars. The preferred hosts of this demon include the hackberry, oak, maple, sycamore and other trees and shrubs.

The Io moth caterpillar is found on corn foliage, roses, and a wide variety of trees and shrubs. When mature, the Io caterpillar may reach a length of 2 .5 inches and is basically pale green in color. There is a narrow reddish stripe edged underneath with white that runs lengthwise along each side of the body. The offensive hairs are grouped in clusters on various parts of the body.

My only personal experience with an urticating caterpillar occurred one day when I was about 8 years old and was playing under a large hackberry tree in the back yard of my home in north Texas. I vividly recall I suddenly felt as if someone had thrust a red-hot needle into my back. I ran into the house, and my mother found what she called a Mexican asp (undoubtedly a puss caterpillar) in my shirt. I became nauseous and developed a slight fever, which, fortunately, abated in a few hours.

It is the wise individual who only handles any type of caterpillar he or she may encounter with a gloved hand or forceps.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the July 12-18, 2006, issue

Enjoy The Rock River Times? Help spread the word!