SWARMING DADDY LONGLEGS! The explanation behind the creepy phenomenon

So, fellow nerds, what's with this video circulating on Facebook and Youtube?



First of all, these are not spiders. They are harvestmen or daddy-longlegs. For those of you who remember the ol' mnemonic device for taxonomy, King Philip Can Order Fresh Green Salad (Kingdom, Phylum, Class, Order, Family, Genus and Species), these critters, like spiders, scorpions and ticks, are in the class Arachnida. However, harvestmen belong to their own order, Opiliones.

So what's the difference?

1. Harvestmen have a single cephalothorax and a single pair of eyes. True spiders have a narrow "waist" that creates two segments, the cephalothorax and abdomen.
2. Harvestmen have a single pair of eyes. True spiders most commonly have eight eyes, however they can have no eyes, or as many as 12 eyes.
3. Harvestmen are nonvenomous.
4. Harvestmen have no spinnerets, so they do not spin webs.
5. Harvestmen are older than spiders--the oldest fossil, from Scotland, is at least 400 million years old. True spiders are about 300 million years old.
6. Harvestmen are omnivores--they eat dead stuff, bird droppings, fungus and small arthropods and slugs.

Finally, the question every one is asking. WHY DO THEY DO THIS? They mass for defensive purposes, and to keep themselves warm. Harvestmen possess a pair of stinky glands called ozopores; when they mass, the combined smell can be quite disturbing. Swarming also makes them appear larger. When disturbed, the entire throng will sometimes bob and sway--a truly unsettling effect.

Learn more about harvestmen/daddy long legs:

http://spiders.ucr.edu/daddylonglegs.html

http://www.newsweek.com/video-science-explains-why-thousands-daddy-longlegs-swarmed-house-312362

http://mentalfloss.com/article/59455/15-fascinating-facts-about-daddy-longlegs