You're undoubtedly familiar with daddy longlegs, those incredibly long-legged arachnids commonly found around the outside of houses, among other areas. More than 6000 unique species of daddy longlegs throughout the world, but did you know that they aren't spiders at all?
Daddy longlegs certainly look a lot like spiders, with their eight legs and their fangs, but the similarities pretty much stop right there. Daddy longlegs are of the order Opiliones, while spiders are of the order Araneae. Both are arachnids, but their many differences make daddy longlegs more similar to other arachnids, like scorpions, ticks or mites.
A few key differences include the number of eyes, daddy longlegs have just two, while spiders generally have eight. Also, the lack of venom or silk. And perhaps most important, daddy longlegs have just one body part, whereas spiders have two, with an abdomen separated from the cephalothorax.
To add to the confusion, though, there are some spiders that have gained the name, daddy longlegs spiders, due to their long legs. These species, also known as cellar spiders, do have a separate abdomen and other true spider characteristics.