Eight Legs, Two Fangs, and an Attitude

Yes, that is in fact another movie reference, this time for the popular 1990 film Arachnophobia. Many Americans inspected their shoes and the toilet before getting to business after this movie. And with good reason! Fright from spiders is one of our most basic fears, ranking up there with snakes and heights. Some evidence suggests that these fears are innate, having evolved during our development as a species to increase survival. However, fear of spiders in the Northeastern United States is based more in fiction than in fact.

With eight legs and two body parts, spiders belong to a group of arthropods called arachnids; a title shared by ticks, mites and scorpions. Nope, spiders are neither bugs nor insects, which have six legs and three body parts! Worldwide there is an estimated 40,000 species of spiders, with 3,400 in the US and Mexico representing 64 different families. Identification to the family level relies on several key features, including the number of eyes and their arrangement on the cephalothorax, the body segment that contains the head. For example, spiders may have six or eight eyes arranged in pairs, rows, or clusters. As is true for most specimens requiring identification, habitat and behavioral information are invaluable in determining where a specimen lives and what it does.

Nearly all spiders are predators that feed on other living organisms to obtain nutrition. Most species have mouthparts that open and close sideways like ice tongs, with piercing fangs at the end of jaws called chelicerae. Other spiders, including tarantulas, have mouthparts that move up and down in a stabbing motion. Both mouthpart designs require spiders to liquefy food before consumption, and this is accomplished by injecting digestive fluids into captured prey. Proteins within these digestive fluids break down solid tissue, yielding a soupy liquid ingested by the feeding spider. Prey items are left as hollow exoskeletons or skins after being fed upon by a spider.

In pest management, we often hear the question, “what is the point of _[some pest]_?!” People want to know the role played by mice, clothing moths, ants or mosquitoes, which are commonly viewed only as pests. Sometimes this requires a bit of research to discover not only the ecological role played by an organism, but also the context that will give meaning for the non-ecologist. With spiders, the answer is simple: spiders provide pest control! In my own living space I consider the presence of spiders to be an indicator of spider food. Personally I would rather have the spider! Within reason, I will allow spiders to inhabit the hard to reach corners of a room so long as they do their job and eat invading insects.

Although myth and Hollywood lend to a heightened fear of spiders, there are only a few species of concern in the US. In general, spiders are not very aggressive, and only bite when they are threatened. Most reports of spider bites come from situations where people were sleeping and rolled over a spider, or someone put on an article of clothing that contained a spider. With no ability to make noise, a spider announces its presence the only way it can - with a bite. Reactions to a spider bite can range from no visible signs, an itchy raised bump, to severe cases that include ulcer-like sores or even death. In our area of the eastern United States, the brown recluse and black widow spiders are two species with dangerous and harmful bites.

Brown Recluse

The brown recluse or fiddle-back spider, named for the design on its cephalothorax, is a southern species occasionally introduced to our area with furniture, boxes or other items shipped north. Measuring 1/3 inch, they prey on small, soft-bodied insects and are active at night or in dimly-lit rooms during the day. Although their bite is not painful, the venom of a brown recluse spider contains a powerful cytotoxin that causes tissue death. Large ulcerating sores can form several days after a bite and require immediate medical attention. The presence of a single brown recluse spider in a home is enough to warrant action.

Black Widow

A second species of concern is the infamous black widow spider. Identified by her jet black abdomen with a contrasting red hourglass, this spider can be found in almost every state in the US, excluding Alaska. The danger posed by black widow spiders exceeds that of brown recluse based on the nature of the toxin. While brown recluse venom is cytotoxic, black widow venom is neurotoxic and can therefore create a systemic or whole-body reaction. On a per volume basis, black widow venom is more potent than that of a pit viper, but because it is injected in low levels, death is rare. Black widow bites are most dangerous to small children and the elderly.

Where to Look

Both black widow and brown recluse spiders can live indoors, where they hide in dark, infrequently disturbed spaces behind and under furniture, in basements, garages and closets, and with stored items. Webs are irregular in shape and typically found close to the ground. Outdoors, these spiders prefer to construct their webs in debris piles, in corners near windows and under the eaves of a house. These are areas visited by prey and ideal locations for a web.

Pictures of these and other spiders can be found on Bugguide.net. Some of the spiders more commonly received for identification at JP McHale include wolf spiders, cellar spiders, sowbug killers, yellow garden spiders, nursery web or fishing spiders, long-legged sac spiders, crab spiders and jumping spiders.

Spider Myths

Chances are you have heard one of the many variations about eating spiders while you sleep. Whether it is 4 spiders a year or 20 in a lifetime (which leaves interesting mathematical disputes), you would be hard-pressed to find any evidence to suggest that this is true (thank goodness). Myth Busted: we do not eat spiders in our sleep, nor do they obtain moisture from our eyes or mouth while we dream.

“Daddy-long-legs are one of the most poisonous spiders, but their fangs are too short to bite humans.” Actually, the truth about this one is comically ironic. First, the arachnids commonly referred to as daddy-long-legs are not spiders, but instead belong to a group called Opiliones or Harvestmen. What’s more? Harvestmen are not venomous and lack fangs altogether - they do not even bite! Myth Busted: harvestmen are docile predators and scavengers that contain no toxic venom.