Frequently Asked Questions about Spiders
Question: Do spiders urinate? (why I get this question so often, I don't know)
Answer:spiders have structures designed to get rid of nitrogenous waste. These are called malpighian tubules and function in a manner similar to our own kidneys. Spiders don't produce urine like we do, but produce uric acid, which doesn't dissolve in water and is a near-solid. Spiders have this alternate form of waste because they can't afford to lose as much water as we do. These malpighian tubules drain into an pouch attached to the digestive tract (called a stercoral pocket) so the uric acid waste from the "kidneys" is combined and eliminated together with solid waste from the digestive tract. In this sense, spiders don't deposit separate feces and urine, but rather a combined waste product that exits from the same opening (anus).
Question: how many kinds of spiders are there?
Answer: As of January 2005, there were over 38,000 separate, scientifically described and recognized species of spider known. There may be as many as double this number that are currently unknown to science (but this is probably a high estimate). As a reasonable comparison, there are 10,000 or fewer species of birds on the planet.
Question:Are all spiders venomous?
The majority of spiders possess venom. A notable exception is the family Uloboridae comprising a couple of hundred species that lack venom glands entirely. Although most spiders have venom, the vast majority are not poisonous to humans. Of the 38,000+ species that are known, perhaps a couple dozen or so have venom powerful enough to kill a human or cause serious health problems.