Monday, June 23, 2008 - by Kyle Waggener, Chattanooga Nature Center
Are Granddaddy-longlegs the most poisonous spider in the world but their fangs are too small to bite us?
Actually, granddaddy-longlegs are not spiders. They are a type of arachnid, along with spiders, ticks, mites, and scorpions but they belong to a group called harvestmen not spiders. Also they are usually called “daddy-long-legs” in field guides not “granddaddy-longlegs” and are more appropriately called harvestmen.
There are several differences between harvestmen and spiders. Spiders have two body parts, a cephalothorax (head and thorax fused together) and abdomen. Harvestmen have one body part similar to ticks and mites. The cephalothorax and abdomen are fused together so harvestmen lack the narrow “waist” that spiders have.
Harvestmen have two eyes. Nearly all spiders have eight. Harvestmen don’t have silk glands or spinnerets so they can’t spin a web like most spiders do. If you see a harvestmen in a web, it is soon to be a meal for a spider.
Harvestmen do not have venom glands or fangs, which all spiders have.
Spiders feed on live animals that they paralyze or kill with their venomous fangs.
Harvestmen eat decomposing plant and animal matter mostly, with an occasional slow-moving insect as part of their diet.
It is more correct to use the term venomous than poisonous to refer to spiders. Poison is ingested and venom is injected. In poisonous animals, toxic chemicals are stored in the body tissues and are used as a defense to prevent the animal from being eaten. Venom is usually used as a means to obtain prey, with the venomous animal injecting the toxic chemicals into the body of another animal. So spiders are venomous not poisonous. Predators can eat spiders, even brown recluse spiders, without ill effects.
So, even though “daddy-long-legs” aren’t the most “poisonous” arachnid in the world, they are still a very valuable part of the ecosystem. Maybe now more people can enjoy letting one crawl around on their hand without any fear of venomous fangs. If you really think about it, half of them are really “mommy-long-legs” anyway!