Spiders are arachnids. Depending on what source you look at, there are 10-12 different types of arachnids. Spiders are one type of arachnid or one order with the fancy name Araneae (pronounced a-RA-nee-ee).
All arachnids have eight legs, two body parts (sometimes fused to look like one), never any antennae, and never any wings. In addition to the eight legs, arachnids have a pair of pedipalps or palps. In spiders, the palps look like a short pair of legs near the mouth. In scorpions, the palps are modified into claws. The Amblypygi arachnids (aka tailless whip scorpions) have awesomely large palps modified into grasping arms. Check out this video of a tailless whip scorpion hunting!
What makes Araneae (spiders) special are spinnerets or silk producing glands located on the end of the abdomen, what looks like a “waist” which attaches the head and abdomen together, and a venomous bite. Other kinds of arachnids include vinegaroons (Uropygi), ticks and mites (Acari), scorpions (Scorpionida), and harvestmen AKA Daddy-long-legs (fancy name, Opiliones). I only named 5 orders out of the 10-12 depending on what source you reference, so know that there are ones I’m missing. Check out the book Arachnids by Jan Beccaloni if you’re curious about arachnids in general. This is a go-to reference I use all the time.
Only two other arachnids, besides spiders, are venomous: scorpions, and the tiny pseudoscorpion. As you may know, scorpions deliver venom via their “tail”. Pseudoscorpions produce venom in their palps. Never heard of a pseudoscorpion? They are harmless, tiny hunters usually found in soil. When I say tiny, I mean a fraction of your pinkie nail, tiny. The first time I ever saw a pseudoscorpion, I had no idea what it was and have to admit, I was a little freaked out! They look like ticks but with little pincers. I found several pseudoscorpions among egg flats that were being reused as packing material. My curiosity led me to ID them and I was surprised that they were spider cousins. Now, when I see one, I get excited and have to show somebody because they often go unseen and they’re too cool to ignore! More on pseudoscorpions from Penn State University here.
Back to Daddy long legs being an impostor. I’ve emphasized this in my other blogs, that common names are convenient and easy to pronounce, but they cause a lot of confusion. The nickname “daddy long legs” has been given to 2 different arachnids. Only one is a true spider. Can you tell which one?
The one on the right is a male Pholcus phalangioides, or cellar spider, or daddy long leg spider (and depending on locale, I’m sure there are other common names). The one on the left is in the order Opiliones aka daddy long legs or harvestmen. I do not know what kind is pictured. There are over 200 different species of harvestmen in north America. Next time you’re in the woods note how many different kinds of harvestmen you see! Note a few things: the harvestman on the left looks like it has one body part while the cellar spider on the right has 2 distinct parts (or what looks like a longer body). Although not pictured, another giant clue is that cellar spiders are almost always in webs. Harvestmen do not produce silk. At all. The only time you’ll see a harvestman in a web is when it gets trapped in a spider’s web. You wouldn’t be able to tell from the photo, but another huge difference is that harvestmen do not have venom glands. Recall, the only arachnids that possess venom glands are spiders, scorpions, and pseudoscorpions.
My years of camp counselor experience has put me up against some very convinced grade school kids that “daddy long legs is the most venomous spider but its fangs are too small to penetrate the skin’. It becomes confusing quickly when I ask, “Do you mean the spider or the harvestman?” Most of them are talking about harvestmen. I tell them that harvestmen do not even have venom glands. “But my DAD said so!” or “My teacher said so!” are some of the bold arguments I get. So I ask them, “If the fangs are too small to penetrate the skin, then how do we know?” This usually gets them thinking. If all else fails, I tell them that harvestmen aka daddy long legs isn’t a spider, its a spider cousin and to google it! And then I hope they do. A lot of “spider” myths and urban lore are passed along without question. Its the shock factor that is fun to replicate. We all make mistakes (for all you dads and teachers who have made this claim and didn’t know), but mistakes are how we learn! For more on the daddy long legs spider, check out this Myth Busters episode.
In conclusion, spiders are like the rock stars of the arachnids. The other orders don’t seem to get as much attention and are sometimes lumped under the title of “spiders”. In Pennsylvania, we are hyper aware of ticks. They make a close second to the arachnid rock stars, as far as knowing a thing or two about them, but that’s about it as far as most common arachnid knowledge goes. There are many “spider” myths and crazy stories out there; spiders exploding from cacti, the camel spider that eats soldiers alive in their tents, etc. I encourage you to look into some of the arachnids pictured below. All are fascinating in their own way, not just the spiders. The next time you’re out in the woods and a harvestman crosses your path, you can say, “That’s actually NOT a spider” and see what your friends and family say!