Can’t Touch This: The Southern Flannel Moth caterpillar, or Asp, Megalopyge opercularis, will give you a painful sting. Matt Bertone

Asp Caterpillars are making news this week, so I thought I’d dispense some professional entomological advice: if it looks like The Donald’s hair, leave it alone.

Several different caterpillar species look like escapees from Trump’s noggin, and nearly all of them have urticating hairs. “Urticating” is a fancy way of saying highly irritating. (The jokes write themselves here, don’t they?)

Asp Caterpillars (Megalopyge opercularis) have a variety of nicknames: southern flannel moth, puss caterpillar, and the tree asp. They are considered the most highly venomous caterpillars in North America. The “hairs” of these caterpillars can break off and cause itching, but also hide an unpleasant surprise: sharp spines. The spines are connected to venom gland cells, and function like little hypodermic needles. The pain from injected venom is said to be intense, and lasts at least 12 hours.

This caterpillar found in Peru is remarkably like Trump’s comb over. Megalopyge species. Phil Torres

How much does it hurt?

Recent media stories about asp caterpillar stings seem a bit … overly hyped. “Predators Taking Over Florida” is pure exaggeration (as well as inaccurate, since these caterpillars are plant-eaters.) Asp caterpillars are wide-spread throughout the Americas, and while they do have population fluctuations from year to year, they aren’t new or an introduced species. Statements  like “so far no one has died a caterpillar-caused death” suggest Death by Toxic Trump Toupee is a real possibility.

Are these little stinging tribbles really that dangerous? Some people seem to shake a sting off, but others end up in the emergency room. Why is there so much variation?

Fortunately, entomologists are curious people, and there is a long, distinguished history of rubbing stinging insects on yourself for science. The go-to person for entomological pain is Dr. Justin Schmidt, best known as the author of the Schmidt Pain Index; a ranking system calculated from the agony caused by a wide variety of wasps and bees stinging him during his research. While Schmidt hasn’t systematically studied caterpillars, he did say the pain of a caterpillar sting lasted longer than the pain of most wasp or bee stings.

Asp or Puss caterpillar, Megalopyge opercularis (characteristic pattern of sting). Photograph courtesy of Armed Forces Pest Management Board/Donald Hall.

I next contacted Dr. Donald Hall, a medical entomologist from the University of Florida, who has experience working with these caterpillars.  Hall was able to confirm that indeed, the pain of an asp caterpillar sting is extremely unpleasant. He suggested the wide variation in reactions between people who get stung may be in part because of how many spines on the caterpillar are encountered, and where on the body the sting occurs. Someone that just brushes by a caterpillar might get a small, painful sting; someone that steps on a caterpillar, or traps it between fingers, gets a full dose of all the venom over a tender spot.

I asked Hall how much it really hurts: “The pain is a deep, aching pain. It feels like it goes all the way to the bone. If you get stung on the finger the pain radiates up the arm. The swelling can go up to the armpit.”

That was his description of stings he received caring for recently hatched asp caterpillars–they were about 1 cm long, only 1/3 of the size they reach when they are fully grown and ready to turn into a moth. The caterpillars turn around and eat their shed skins as they grow — hairy poisonous spines and all.  Each shed results in a caterpillar with more of a fiery, stinging punch.

Other Hairpieces with Evil Intent

Asp caterpillars are not the only prickly brain rugs you need to look out for in the undergrowth. Eleven different families of caterpillars have urticating hairs.  The Hag Moth Caterpillar looks a bit like Trump on a windy day:

The Hag Moth Caterpillar, Phobetron pithecium, is less stingy than Asp Caterpillars, but still should not be petted.  Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org

Donald Trump. Ross McDairmant/AP

Generally, I try to convince people that insects are harmless, and for the vast majority of species, this is true. But the stakes are fairly high for negative reactions from caterpillar petting, if you don’t know exactly what kind of fuzzy caterpillar you are looking at. Teaching small kids to look but not touch fuzzy caterpillars is also a good idea, at least until they are old enough to learn about Trump Hair.

What should you do if you get stung by one of these caterpillars?

• Use duct tape to remove any spines that may adhere to the area of the sting
• Apply ice packs to minimize swelling and inflammation
• Seek medical help if urticating hairs get in the eyes, or symptoms of anaphylaxis and/or breathing trouble develops
• Swear. Swear a lot.

A handy photo guide to stinging caterpillars of the U.S. is available free via University of Maryland Extension Service.