This is absolutely not true! Daddy longlegs are not spiders and do not have fangs or venom. In the United States, the name “daddy longlegs” is usually used in reference to an arachnid in the order Opiliones. These long-legged animals are found in dark, damp places. In Europe, they are sometimes referred to as harvestmen because people most often notice them during harvest time in the newly cut fields. Although they sometimes prey on insects, they are primarily scavengers, feeding on different kinds of organic material.

One family of spiders, the Pholcidae, also sometimes goes by the name “daddy longlegs spider.”  However, there is no evidence to support the myth that this real spider has venom that is particularly harmful to humans.  You can get more detailed information about this myth at the University of California Riverside spider research site.

Absolutely not! Colorado is not part of the natural range of this spider. Although single specimens are sometimes brought into the state, natural populations are not found in Colorado. 

The brown recluse is the common name for the species Loxosceles reclusa. All species in the genus Loxosceles have venom that can cause necrotic lesions in humans. However, as with the majority of spiders, brown recluse spiders bite humans only when seriously provoked. 

This article from the Dermatology Online Journal provides more information. 

Nope. Black widow females are no more likely than any other female spider to eat their mates.  If the female is ready to mate and if the male sings the right sweet silk song to her, then she will allow him to approach and to mate. If the female is not particularly hungry, she will likely allow the male to leave unscathed after copulation. However, the female black widow, as is common in spiders, is larger than the male. So if she is hungry, she may feed on the male, but this is true of many species of spiders.

Here in Colorado, brown recluse envenomation is the least likely explanation for the nasty necrotic lesion on the arm of your friend or relative, and the physician in question needs to explore other causes.  Whereas brown recluse bites are very difficult to treat or cure, many of the other causes of necrotic lesions can be readily treated if they are properly diagnosed early.

They probably don’t. If you wake up with a series of “bites” on your arm, leg, and neck and you are certain that you do not have a vampire sleeping with you, then before blaming the poor spiders, check your bedclothes for bedbugs. Bedbugs are not a myth. They are flat, secretive insects that hide in cracks and crevices during the day and come out at night to suck your blood. The mysterious bites on your body are far more likely to be caused by mosquitoes, biting flies, bedbugs, lice, or your pet’s fleas than by spiders. So stop blaming my friends!

You don’t really want to know. Nearly every spider you see is “poisonous” because nearly every species of spider on earth has fangs and venom. What you really meant to ask was how many species of spiders in Colorado have venom harmful to humans. There are over 48,000 described species of spiders on Earth. Of these, only a mere handful have venom of concern to humans.

The most common species of spider in Colorado with venom that is harmful to humans is the western black widow spider, Latrodectus hesperus. This spider’s venom is a neurotoxin and can cause excruciating pain in the limbs, a tightening of the stomach muscles, facial contortions, sweating, and other unpleasant symptoms. 

If you are ever bitten by a black widow, you are unlikely to die but very likely to wish you were dead. Fortunately, these spiders are very easy to recognize and are extremely timid and very unlikely to bite.  Antivenin is available in most hospitals and poison control centers. The antivenin is extremely effective and will eliminate the symptoms almost immediately. However, many physicians are, for some reason (perhaps due to the serum in which the antivenin is stored), often reluctant to administer the antivenin.

Other species found in Colorado that have been accused of causing necrotic lesions are two species of Clubionidae spiders, Cheiracanthium mildei and Cheiracanthium inclusum, commonly called the yellow sac spiders and an Agelenidae spider, Eratigena agrestis, commonly called the hobo spider. The latter species was introduced into the Pacific Northwest from Europe and has been slowly spreading eastward. 

However, the evidence supporting these three species as the causative agents of necrotic lesions is extremely weak. At the present time, there is no cause for undue concern about these spiders.

Sadly, this is a widespread internet hoax. Rick Vetter, the author of this website, and his colleague, P. Kirk Visscher, traced the hoax to its originator and published an entertaining article about the hoax and how quickly it spread across the net in the Winter 2000 issue of the magazine American Entomologist, published by the Entomological Society of America.

If you are ever bitten by an arthropod (insect or spider) or stung by an arthropod such as a bee or an ant and begin to experience unpleasant symptoms, you should go see your doctor. But do not go alone. If you can, take the six- or eight-legged suspect with you, even if the culprit is, by that time, dried up or squashed. It is nearly impossible to administer an effective treatment against symptoms caused by an arthropod sting or bite unless (1) it can be verified that the wound or symptoms were indeed caused by an arthropod and (2) the arthropod can be identified. The treatment for a black widow bite (antivenin or serious pain killers) is going to be quite a bit different than the treatment for a jumping spider bite.