Summary: Caterpillars are brightly colored or camouflaged to protect themselves from their predators. Some caterpillars have hairs or spines that are loaded with poisons that will give you a painful sting if you touch them. Resist the urge. I have been stung myself and it is no fun.
Caterpillars are the larval stage of butterflies and moths. They are often brightly colored and they feed on the foliage of many different kinds of trees and shrubs. Caterpillars have developed defense mechanisms that protect them from predators. Their bright colors serve as a warning sign to potential predators telling them to beware of toxic treats. Caterpillars are sometimes covered in hairs or spines that are venomous and can easily break off if you touch them causing joint pain and swelling. Even caterpillar cocoons can be unsafe to touch.
Some caterpillars have hairs or spines as that only mimic their more toxic cousins. These caterpillars are not toxic, yet fool their predators by looking like the more toxic variety. Because caterpillars are so good at fooling their predators, it is very difficult to determine whether a caterpillar is or is not toxic just by looking at it. The only way to find out for sure would be to touch it, which is sort of a bad return on investment. Caterpillar stings can cause welts that last for weeks, and some species of stinging caterpillar can even cause death. Caterpillar venom is not usually considered deadly, although small children might be at serious risk if they pick up a brightly colored caterpillar and eat it, thinking it might taste good.
Although the great majority of caterpillar species are not toxic I would recommend being cautious by avoiding touching any caterpillar, especially the brightly colored, hairy varieties that look so cute and cuddly. Many caterpillars that do not actually produce venom can still cause an allergic reaction because their fine hairs disperse in the air and can be breathed in or irritate human skin. Even the bristles on the relatively harmless and sometimes domesticated wooly bear caterpillar can cause skin irritation. And, you don't touch a dead or slightly smushed caterpillar, either. They have just as much toxin in their bodies as living caterpillars.
Caterpillars will sometimes explode in numbers during certain times of the year, and some years there are more caterpillars than others. Children should be warned about the dangers of touching them if there are a lot of stinging caterpillars outside. When examining for stings look for a row or several rows of red insect bites. They can last anywhere from a few days to several weeks and have varying amounts of pain or soreness.
Here are some different types of stinging caterpillars, what they look like, where they are found, what they like to eat, and what you can expect if stung by one.
Saddleback Caterpillars are brown-red in appearance, about 2 cm long. They have fleshy horns with spines on each end of their bodies and shorter horns with spines on each side. They have a distinct green coloring on their midsection that looks like a saddle. There is a brown or purple circle in the middle of the bright green saddle section. Saddlebacks are common across North America and frequently appear in late summer or early fall. They feed on apple, basswood, cherry, chestnut, dogwood, elm, maple, oak, plum, and corn.
Gypsy Moth Caterpillars are a blue green color as young caterpillars. Their color fades to a blue-grey as they get older. They are covered in spiny, stinging hairs and have round bumps on each of their body segments. They are blue behind their head, red on their rear, and yellow on the sides. The gypsy moths usually exist in low numbers, but outbreaks can be major factors in the defoliation of trees so they are considered a pest beyond their stinging potential. During times of outbreak, the gypsy moth caterpillar droppings and the sound of their chewing is also an annoyance. They were brought to America in the mid 19th century to begin a silk industry that never materialized. They are now entrenched as one of the most harmful pest to hardwood trees in North America.
Hag Moth Caterpillars are brown or red-brown and only a centimeter or two in length. They are covered in hairs and have nine pairs of spines running down their back. Some of the spines become twisted together so the caterpillar looks like it has locks of dirty, tangled hair, earning them the name Hag. They deliver a painful sting similar to the saddleback caterpillar. They are found in the Eastern and Southern US, prominent in August and September, and feed on apple, birch, chestnut, dogwood, hickory, oak, sassafras, and willow.
Tussock Moth Caterpillars in their many varieties, are hairy and brightly colored with long hairs on both of their ends. These hairs are often in clumps, or tufts, giving the caterpillar its name. The hairs break off very easily and cause skin irritation. There are many varieties of tussock moth caterpillars that feed on a wide range of plants. One example is the aptly named toothbrush caterpillar, which has several venomous, toothbrush-like bristles on its back.
Puss Caterpillars are pear shaped and covered in long, shaggy looking hair that is dirty white to a yellowish brown in color. They are found throughout North and South America. The hair on their back ends looks like a tail but hides venomous spines. These caterpillars look very soft, like a tiny Persian cat, which is probably how they got the name œPuss. However, despite their fluffy appearance these caterpillars give a particularly nasty sting that often develops into a persistent rash. They are communal feeders on apple, elm, hackberry, maple, pecan, oak, sycamore, and citrus trees. They sometimes fall from trees and land on people, giving them sharp stings on their necks or arms. Sometimes a severe reaction can occur from a puss caterpillar sting. Symptoms might include headache, fever, nausea, vomiting, respiratory distress and in extreme cases seizure and abdominal pain. Their stings have a grid-like pattern that can last for several weeks.
Browntail Moth Caterpillars are hairy brown caterpillars 2 or 3 cm in length with red spots on its back and white hairs on its sides. Their hairs can easily break off and cause irritation to the skin... They are distributed worldwide and feed on blackthorn and hawthorn shrubs, as well as on fruit trees, mistletoe, and many other deciduous trees.
Buck Moth Caterpillars often increase in numbers during the fall hunting season, which is how they got their name. They have breakaway spines on their back and sides and have a sting similar to the saddleback. They have a dark red head, grey-brown body, yellow and white spots and orange spines on their back and longer red or black spines on their sides. They are found in oak trees in the Southeastern and Southwestern states. I think this was the kind of caterpillar I was stung by. The red, rash like bumps last about a week and feel tender and painful.
South American Lonomia Saturniid Moth Caterpillars are a dangerous group of caterpillars that inflict very painful stings that can cause internal hemorrhaging, renal failure and for several unlucky victims each year, death. They have camouflage colors of green or brown that helps them to blend into their environment. They are communal feeders that sometimes gather on the trunk of trees where sometimes an unwitting, unfortunate soul leans against them and gets severely stung. The benefit of these insects is that they have provided scientist with chemicals that help to prevent blood clots. They are only found in South America, but I'll tell you about them because you are better off knowing, than not.
Other stinging caterpillars include the Io Moth Caterpillar, the Silverspotted Tiger Moth Caterpillar, and the Stinging Rose Caterpillar. This is not meant to be a complete list, but a list of some of the common varieties you need to watch out for in North America.
If you see a caterpillar crawling on your skin do not rush to swat it off because this could cause spines to get stuck onto your hand. Gently lift the caterpillar off with a stick or pencil. If you are stung by a caterpillar don't rub the affected area, this might cause spines to become more imbedded in the skin. Take a piece of sticky tape and try to pull out any hairs or spines by placing the tape on the skin and pulling it off. Do this several times until all the spines are removed. Wash the area with soap and water. If you are stung on the hand you should remove any rings immediately because the fingers might swell up. To easy the sting you can place an ice pack on the sting site, rub alcohol or ammonia on it, rub on an antihistamine or cortisone cream or take a antihistamine orally.
To prevent caterpillar stings you need to be aware of when the caterpillars are in their peak larval instar season. This is normally late fall, but can also occur in the spring in tropical climates. The caterpillars will be around in greater numbers during this time. You might want to wear long sleeves and a hat with a wide brim if you are walking outdoors under a lot of trees with caterpillars in them. Also, the hairs of a caterpillar can be spread into the air and cause allergic reactions in some people. Keep your windows and doors closed and make sure you have clean air filters on any air conditioning system that brings in air from the outside. Don't hang wet clothes out to dry because hairs or spines might fall onto them.
Caterpillars are beautiful, interesting creatures that develop into harmless moths or gorgeous butterflies. Look but don't touch is my best piece of advice.