Here's something you probably didn't know: Daddy longlegs both are and aren't spiders. That's because "daddy longlegs" is an informal term that can refer to two separate groups of animals. If you think back to biology class, you may remember that organisms are classified by a branching family tree of terms: Kingdom is at the top and branches off into different phyla (singular "phylum"), which in turn branches off into classes, then orders, families, genuses, and finally species.

Both types of daddy longlegs are in the class Arachnida — a category that contains everything from scorpions to ticks to spiders — but they're in different orders. The most common type of daddy longlegs, which some people also call "harvestmen," are in the order Opiliones. But there's another type of daddy longlegs (these ones are sometimes called "cellar spiders" and officially called Pholcidae) that's actually a spider, since it's in the order Aranea with every other true spider you know. You can tell the difference between the spider and non-spider daddy longlegs by their body shape. Spiders have segmented bodies; the bodies of harvestmen are all in one piece.

So right out of the gate, this playground legend is already kind of useless; the two kinds of daddy longlegs aren't even that closely related, so they can't both have the deadliest venom. And as a matter of fact, neither of them does.

When it comes to harvestmen, you might as well be just as afraid that a ladybug will bite you. These bugs don't have venom glands, fangs, or anything else they can use to subdue prey. They generally eat decomposing plants and animals, killing small prey here and there when the opportunity presents itself. But humans? As the saying goes, they're probably more scared of you than you are of them.

Cellar spiders do have venom and fangs, but for them, the legend just isn't based in fact: There's no evidence that their venom is toxic to humans, but there's also no evidence that their fangs can't penetrate human skin. According to entomologist Rick Vetter, there are no studies that have tested how lethal their venom is to mammals — even to lab mice. And while their fangs are pretty small, Vetter points out that they work the same way as the fearsome brown recluse spider, which is certainly able to bite humans. Most likely, a cellar spider could bite you, but it wouldn't cause much harm.

In the end, it's best to treat these creatures like any other harmless species: leave them be. If they're in your home, you could try trapping them under a glass and taking them outside. But playground legends aside, they're not a threat — no matter which daddy longlegs you're actually talking about.

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To identify the other critters you encounter every day, check out the National Audubon Society Field Guide to Insects and Spiders. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.