A hairy caterpillar: a ginger toupee, twitching cartoonishly | Helen Sullivan

On the trunks of small magnolia trees, in the corner where a table leg meets a table top, on a low damp wall in the shade – here the hairy caterpillars gather together. They travel in long lines, they sleep as close to each other as possible (displaying, it is called in science, a high level of “gregariousness”), as though the scariest thing a predator might see is a cat’s disembodied tail or retched-up fur ball, or a too-small itchy blanket.

If you take a picture of a hairy caterpillar and put it on the internet, a stranger will tell you that you can safely touch it, while another will say you can’t under any circumstances. “What about that says, ‘Touch me’?” one person will ask. “People really need to get a grip,” another will write. “The caterpillars which are hazardous to touch are the hairy Marys, which have hollow hairs with venom. The hairy Marys are very obviously hairy.” This person sounds exactly like an older kid talking to a younger one.

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But you might learn, from people who feel passionately about these things, some good names for hairy caterpillars: spitfires, the aforementioned hairy Marys, fire spitters, furry caterpillars, fuzzy caterpillars, saltmarshes, woolly bear caterpillars.

From a dictionary you will learn the word caterpillar might come from the French chatepelose or “hairy cat”, and the word piller, “to ravage”. In Swiss German they’re called “devil’s cats”.

For a few weeks a year when I was in school, they were the most exciting thing happening at break time. A creature that stayed in one spot, left you alone, but made you feel you were brave just for looking at it. “Don’t touch them!” a group of older children would warn a group of younger ones.

That is what older children are there for: to make absolutely sure that you become obsessed with something they tell you is too dangerous for you to be able to handle. This is the plot of Frozen: an older sister with magical powers (of womanhood) must keep them and herself from her little sister, for her benefit.

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In Texas there is a myth that woolly bear caterpillars can predict the severity of the coming winter. They’re black with a ginger stripe in the middle: the wider the black bands, the worse the winter. Also in Texas is the puss caterpillar, or asp, which looks like a white moustache or ginger toupee, twitching cartoonishly (the soft hairs hide sharp spikes). They turn into moths that look like Yosemite Sam; their venom contains a protein that forms a ring and punches holes in your cells (it really hurts).

The Wikipedia description of asps is unusually tender: “The inch-long larva is generously coated in long, luxuriant hair-like setae, making it resemble a tiny Persian cat … The middle instar has a more dishevelled, ‘bad-hair-day’ appearance, without a distinctive tail.”

Under that fur coat – like a person getting changed under a towel, or a hand moving quickly under a blanket to trick a cat into playing – the caterpillar is getting ready to spin a cocoon, digest itself, and turn into liquid. What survives? Groups of cells called imaginal discs .

Each disc turns into a different body part, like a case containing discs for different stages of a video game, or different letters of the Encyclopedia Britannica. All caterpillars have these discs: they’re basically crawling CD cases . From stinging hairs to the soft powder on wings, from wriggling and marching always into the shade to flying headfirst into lightbulbs. From huddled together, to all alone.

• Helen Sullivan is a Guardian journalist. She is writing a memoir for Scribner Australia

• Do you have an animal, insect or other subject you’d like to see profiled by this columnist? Email helen.sullivan@theguardian.com