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Stinging Caterpillar Identification -- A Quick and Easy Guide
Stinging Caterpillar Identification: What You Don't Know CAN Hurt You!
Most people know that some caterpillars can sting or otherwise defend themselves, but many people don't know which ones to avoid. Most caterpillars are completely harmless, but unless you want an itchy sting, it helps to know which ones to leave alone
The stinging caterpillars featured in this quick and easy guide are all found in North America, and many of them are quite common. They are also all moth caterpillars -- there are no butterfly species in North America with larvae proven to have stinging capabilities. When a caterpillar is able to sting, it's due to the presence of "urticating setae," which means they have stinging hairs or spines. Each little spine is loaded with a small amount of irritating toxin that causes the sting when you touch them.
Caterpillars keep to themselves, and would never attack you or pursue you (they're probably not fast enough!). Their venom is used solely for self-protection. However, on occasion they do come into accidental contact with humans, and that's when stings can occur.
None of the caterpillars in North America are capable of delivering a fatal or even very serious sting, although there is a species in Brazil that can and does kill people with its sting (see this article, "A Deadly Caterpillar," for more information about that species). Still, the sting of some of these caterpillars, particularly the Asp in the Limacodidae family and the buck moth caterpillar in the Saturniidae family, can cause a pretty severe reaction that can hurt for hours.
Stinging Caterpillar Identification: Acharia stimulea
Also known as the saddleback caterpillar, this species is one of the most common and frequently encountered stinging caterpillars in North America. This species feeds on a wide variety of trees, many of which you may have in your back yard -- hackberry, wisteria, elm, grape, and cherry, to name a few. The saddleback caterpillar feeds on the upper side of the leaves, sometimes in small groups (this likely maximizes the stinging power). They're about an inch long when fully grown, and their green-brown pattern makes them easy to see.
Like many of the caterpillars on this list, Acharia stimulea belongs to the family of moths known as the Limacodidae. Many of these caterpillars are brightly colored, and some tropical varieties are so striking they must be seen to be believed. Nearly all of the caterpillars in this family have stinging spines or hairs that they use to defend themselves from predators like birds, toads, and mice. Unfortunately, they can also sting you, even if you simply brush against one while gardening. The sharp hairs detach easily and stay in your skin, causing irritation and a stinging rash.
What To Do If a Caterpillar Stings You
The first imperative is this: Get the stinging hairs out of your skin! This isn't easy, since stinging caterpillar hairs often have hooks or barbs that keep them in your flesh. The best and first thing to do is get packing tape or duct tape, or even waxing tape, and press it into the area. Pull it off and along with many of your arm hairs, the stinging hairs still in your skin should come out. You can also soak the affected area in warm water and try this treatment afterward, in the hopes that the soaking loosened any remaining hairs.
The moth of A. stimulea is a pretty dark brown color with little white spots on the tips of both wings. The amount of markings, and even the color, can show a wide range of variation from individual to individual. The moths don't sting -- as a matter of fact, no moths can sting. It's only the caterpillars you have to worry about.
Stinging Caterpillar Identification -- Phobetron pithecium
This interesting-looking caterpillar is also known as the "monkey slug." Those odd-looking "legs" that extend from each side are actually just fleshy horns, but they're covered with stinging hairs (known scientifically as "urticating setae"). When the monkey slug moves, the strange extensions along its back wobble and move, and it looks somewhat like a miniature monkey walking along.
Stinging caterpillars in the Limacodidae family, which includes the monkey slug, saddleback and several other stinging caterpillars illustrated in this guide, are sometimes called "slug caterpillars" due to their lack of the usual arrangement of legs that most caterpillars have. Instead of three pairs of grasping legs in from and several pairs of fleshy, "soft" legs in back like most caterpillars, slug caterpillars have sticky "suckers" on the underside of their body. These simple sucking feet grasp onto the surface, and the caterpillar moves slowly along. The rippling motion of the suckers gives these caterpillars a distinctive "gliding motion" when they walk. They are very different from true slugs, which aren't caterpillars and don't turn into moths. Slug caterpillars also don't leave a slime trail.
When it's full grown, the caterpillar makes a tough, capsule-like cocoon. Stinging caterpillars like the monkey slug often weave their stinging hairs into their cocoons, which gives them further protection against predators like mice. If you pick up the cocoon of the monkey slug, you may feel a nasty little sting.
This caterpillar turns into a moth called the hag moth. It's a bit of a puzzle how it acquired that insulting name, since the moth isn't very witchy or ugly -- it's just a modest-colored yellow-brown insect that is seldom seen, or noticed, by most people.
Monkey Slug Walking
Stinging Rose Caterpillar
Stinging Caterpillar Identification -- Parasa indetermina
The beautiful caterpillars illustrated above are the larva of a moth in the genus Parasa. There are several species, and all are quite similar. The striking shape and color of the stinging rose caterpillar is typical of the Limacodidae, who don't try to blend in with their surroundings, as most caterpillars do. Stinging caterpillars, and stinging or poisonous insects in general, often sport bright colors and strange shapes. Scientists who work with insects (entomologists), theorize that the high visibility of these creatures may be a way to warn predators not to mess with them. This is called "aposomatic" coloring, and it's a fairly common ploy throughout the animal kingdom -- think of the bright yellow and black coloring of the yellow jacket, for example, whose stripes may be warning colors that protect the animal from even having to use its sting.
Parasa caterpillarscan be quite common on your rose bushes. It's all too easy to brush up against one of these larvae when you're gardening or working in the yard. The sting is not severe, akin to a stinging nettle, but for sensitive individuals it can trigger a more general allergic reaction. If you are ever stung by a caterpillar, follow the suggestions above and watch for symptoms of an allergic reaction. It is possible to develop a more severe systematic reaction.
The moths in the Parasa genus are lovely, with pale green furry bodies and green markings on the wings. They are very well camouflaged among the green leaves of the rose plants where they rest and lay their eggs. The adult moth's camouflage is a nice counterbalance to the bright, "look at me" colors of the caterpillar, and there's a good reason for this: the moths don't sting. When you don't have a good means of self-defense, your best bet for not being eaten is to quietly blend in with the scenery...
Stinging Caterpillar Identification -- Euclea delphinii
Euclea delphinii is also known as the spiny oak slug. This interesting caterpillar feeds on a variety of trees and bushes, including willow, redbud, maple, cherry, and sycamore, in addition to many varieties of oak. It can be found in late summer, when it leaves the safety of its food plant to find a good place to spin its tough, oval cocoon. These bright, beautiful caterpillars follow the general rule of Limacodids and many other stinging insects: be visible, be obvious, and trust that the shrew thinking about eating you will remember that bright insects look that way for a reason -- many of them can sting!
It's important to stress that very few caterpillars can actually sting, and those that do are rarely encountered. Still, it's always wise to handle with care whenever you come across any insect. They may look small and harmless, but sometimes they have a very well-developed self-defense mechanism.
The adult moth of the spiny oak slug is known, appropriately, as the spiny oak slug moth. It's a small insect, and easy to miss unless you know what you're looking for. They sometimes come to lights. These moths are deep chocolate brown, with variable markings of deep orange and bright green. They're really very pretty, and it's a shame most people will never see one, even if it's more or less under their nose.
Spiny Oak Slug Moth
Stinging Caterpillar Identification -- Megalopyge opercularis
Also sometimes called the Elvis caterpillar for its elaborate hairstyle, Megalopyge opercularis is more commonly known as the asp or puss moth caterpillar, especially in the south. This caterpillar claims a lot of victims in late summer, when the caterpillars often simply drop out of trees on their way to burrowing into the ground to pupate. When that happens, they can fall onto an innocent bystander's arm or neck, and the stinging spines hidden in the luxurious fur deliver a very potent sting. The entire area may swell and ache for hours or even days, and some poor unfortunates develop an allergic reaction that can land them in the hospital. In some parts of the south and in some seasons, people hesitate to go out for fear of an asp caterpillar dropping out of a tree onto them.
According to an excellent article at Neuro.com, "Puss moth caterpillars can pose a genuine health hazard. Intense, throbbing pain develops immediately or within five minutes of contact with the caterpillar. Stings on the arm may also result in pain in the axillary (armpit) region. Erythematous (blood-colored) spots may appear at the site of the sting." Clearly the sting of the asp is a serious event, and medical care should be sought if the victim appears to need more than topical relief.
Stinging Caterpillar Identification -- Hemileuca maia
This caterpillar often occurs in colonies of dozens of individuals, which gather together on tree branches to rest. In this situation, you could easily put your hand against an entire group of these stinging caterpillars, which would cause a pretty severe sting. Also known as the buck moth, this species occurs throughout the East. Related species occur throughout the South and West, and they all sting.
The moth that this caterpillar makes is a truly beautiful creature with black and white wings and a red-tipped body. Unlike the caterpillar, the moth cannot sting.
Buck Moth Adult
Do Stinging Caterpillars Make Stinging Moths?
People sometimes wonder if the stinging caterpillar species grow into moths that also sting. The answer is invariably "no." There are no stinging moths of any note, although there are reports of tropical silk moths -- related to the Io moth and the buck moth -- that can release irritating hairs and fur if they are attacked by predators. People, fortunately, are usually not included in the list of moth predators.
Stinging Caterp illars -- Automeris Io
This species is related to the buck moth, and shares many of the same characteristics. It's a large caterpillar, and sometimes occurs in groups. The spines on the caterpillar's body bear a potent venom that creates a sting not unlike a wasp or a bee. The moth is especially striking, and is sometimes called the bull's-eye moth. When it's disturbed, the upper wings pop up and the big eye-spots look like the eyes of an owl or a similar animal.
The Io Moth
This Caterpillar Can Kill You
This is the larva of Lonomia obliqua, the most dangerous caterpillar in the world. Its venom can trigger a runaway reaction that results in internal bleeding, and if the victim doesn't seek medical help it can be rapidly fatal. In southern Brazil, where this caterpillar is not uncommon, farm workers often get stung by the well-camouflaged caterpillars.
For much more information about Lonomia oliqua, see this story: "A Deadly Caterpillar."