Daddy longlegs aren't spiders
Yes, they are arachnids, but so too are mites, ticks, scorpions and other eight-legged creatures. Daddy longlegs belong to the order Opiliones and are more closely related to mites or scorpions than spiders.
Cellar spiders are often confused with daddy longlegs. These spindly-legged spiders are arachnids of the order Pholcidae. According to UC Riverside, "Previously the common name of this family was the cellar spiders but arachnologists have also given them the moniker of "daddy-longlegs spiders" because of the confusion generated by the general public."
So sure, it might be a spider that you're calling a daddy longlegs. But the real daddy longlegs aren't spiders at all. There are upward of 6,500 species of daddy longlegs (the real kind) found all over the world.
Daddy longlegs don't have venom
A common urban myth is that daddy longlegs have the most toxic venom of all spiders but their fangs are too small to bite. We now know that these critters aren't even spiders, and to thoroughly debunk the myth, daddy longlegs don't have venom glands or even fangs. So no, if you come across a daddy longlegs in the garden, you aren't looking at a deadly creature.
Even if talking about daddy longlegs spiders — or cellar spiders of the order Pholcidae — they can indeed bite a person, but don't have venom that harms humans, as "MythBusters" proved.
Daddy longlegs can't make webs
More features that set daddy longlegs apart from spiders are that they don't form webs, or even make silk. They also have a pill-shaped body, without the "waist" that spiders have between body segments. They have just two eyes — not eight — and they can each chunks of food, not just liquids.
Daddy longlegs are ancient
The Opiliones hit their stride a long time ago and have barely changed at all over millions of years. Fossils have been found in rocks and sedimentary deposits with ages of more than 400 million years old.
“We know from a very well preserved fossil of a daddy longlegs from Scotland that they are at least 400 million years old,” researcher Ron Clouse tells Erin McCarthy of Mental Floss. “It is believed daddy longlegs split off from scorpions, which were becoming terrestrial about 435 million years ago. To put this in perspective, this is about 200 million years before dinosaurs appeared, which were only around for about 165 million years.”
So they arrived on the scene well before the dinosaurs and have lasted well after they were gone.
Daddy longlegs play dead to avoid predators
Sure they have long legs, but they aren't really into running away when faced with danger. Daddy longlegs will just curl their legs in and play dead if they're disturbed. The hope is that along with their excellent camouflage color, a predator won't be able to see them if they aren't moving. They'll play dead for several minutes, just to be sure they're out of danger.