The larvae/caterpillars of the Southern Flannel Moth are 3/4" pieces of Hell Fire. The first time I met one of these b@st@rds I was around 10-12 y/o, mowing grass and I dragged my arm across a oak sapling limb and within 5 minutes, my arm was on fire radiating out from the elbow and within 10 minutes my arm was numb and my armpit was in pure pain. I was alone and just took quite a few aspirin and laid down. I thought I was gonna die. Florida has some plants and creatures that will make you learn to pay close attention to your surroundings. They don't look like the demons of pain that they are.

Incidentally the adult version is very beautiful. It belies the death they contained as a larvae. (I know some women like that.)

The Southern Flannel Moth larvae (Megalopyge opercularis) or the puss moth caterpillar is one of the most toxic caterpillars in North America. It has spines that can break off if anyone touches them, stick to the skin and release venom. After about ten minutes, the victim develops red spots feels and experiences throbbing pain which is usually accompanied by nausea, vomiting, stomach pains.
Southern flannel moth (puss moth) caterpillars are teardrop-shaped, and, with their long, silky hairs, resemble a tuft of cotton or fur. Their color varies from yellow or gray to reddish-brown, or a mixture of colors.

 This was something I wrote several years ago along with a piece of an article from a magazine.

 

This article is from Southern Living. I noticed it because it was just updated yesterday, August 18, 2023.

 What To Know About The Southern Flannel Moth, The Region's Most Venomous Caterpillar.

(Incidentally described first by a Smith, J.E. Smith in 1797)
Have you ever heard of the southern flannel moth (Megalopyge opercularis)? Maybe you've seen one, but didn't know what it was. It has a very distinctive, fluffy look (even its wings are covered with silk hairs). If you ever come across one, you definitely won't miss it, but you should definitely avoid it.
The larval form of the southern flannel moth is unique looking as well, and it goes by many names: puss moth caterpillar, tree asp, and woolly slug. More important than its varied nomenclature is the fact that the larval, or caterpillar, form is also super venomous. In fact, it is one of the most dangerous caterpillars in the United States.
How To Identify Flannel Moth Caterpillars
The 1-1.5-inch long caterpillars are covered in long, hair-like setae. These setae have the appearance of animal fur, which is why many say the caterpillars resemble Persian cats. Similar to cats, the colors of the caterpillars may vary from grayish white to a golden light brown with streaks of bright orange, to a dusty charcoal gray. According to the University Of Florida IFAS Extension, (https://edis.ifas.ufl.edu/publication/IN976 *) during its earliest stages, the caterpillar is yellow and has fewer hairs. With each molt, the caterpillar gets hairier and more muted in color. The "fur" is sometimes extremely curly, making the larva look even fluffier.
*Many pictures, more detailed description and information at the UFIFAS link.
Where Do Flannel Moth Caterpillars Live?
Flannel moths have been known to feed on many trees and shrubs, like elms, maples, hackberries, hollies, oaks, and sycamores, according to the NC State Extension. They are commonly spotted in oak and elm trees. Since these plants are frequently found in parks, gardens, and backyards, children are most likely to come in contact with the caterpillars. If you care for children, make sure you teach them about these caterpillars and warn them not to touch them. Basically, if you see a caterpillar wrapped in a stylish fur coat and munching on a tree, shrub, or anything else, it's best to keep your distance.
Southern flannel moth caterpillars are widespread in the United States and can commonly be found on the East Coast in states stretching from New Jersey to Florida. They can also be found as far west as Texas and Arkansas, and also in the desert southwest.
How Dangerous Are Flannel Moth Caterpillars?
Given their appearance and resemblance to soft, fluffy pets, it's easy to understand why people would want to touch the southern flannel moth caterpillar. Unfortunately, the "fur" is nothing like a cuddly, feline friend. It actually contains venomous spines. Coming into contact with these spines will cause extremely painful reactions in the skin. Caterpillars that are more advanced in the larval stage have the most potent defense.
Is The Adult Moth Harmful?
As for the adult southern flannel moth, it's harmless on its own. The moth is covered in lengthy fuzz, not venomous spines, with colors ranging from a dull orange to a bright, lemon yellow, but its fuzzy feet are always black. Though the adult moths do not sting, if they are seen in an area, it is safe and best to assume that the more dangerous larvae are nearby or will soon be born.
What To Do If You Are Stung
The extreme pain-inducing spines are a form of defense meant to protect the caterpillars until they turn into moths and the venomous spines disappear. The slightest amount of contact, even merely brushing past them, will cause the spines to break off the caterpillar and inject venom into the skin. Sometimes, the spines become deeply embedded in the skin and need to be removed using cellophane tape. Placing cellophane tape over the area stung and pulling it off will usually remove most of the spines.
The pain from the southern flannel moth caterpillar sting has been described in several different, but all excruciating ways, a white-hot or knife-like sensation, a pain you can feel in your bones, or even a snake bite, hence why one of the alternative names for the caterpillar is "tree asp."
In the best-case scenario, reactions to the sting are localized to the affected area. However, what happens more often is that the pain radiates throughout the entire limb and eventually the entire body. It can cause burning, swelling, nausea, headache, abdominal pain, rashes, and bumps or marks on the skin. In cases of a severe allergic reaction, some people experience difficulty breathing. Home remedies for mild cases include ice packs, antihistamine, baking soda paste, hydrocortisone cream, and calamine lotion. Emergency medical attention should be sought in cases of extreme reactions.

https://www.southernliving.com/garden/pests/southern-flannel-moth-caterpillar