Spider Information

Spiders – Who is REALLY Biting You?

We attended a continuing education class on spiders. Our Speaker was Rick Vetter, an entomologist. He explained to us that spiders are extremely difficult to identify. It is easier to eliminate what kind of spider the spider is NOT rather than classify what it is. There are over 50,000 species of spiders classified into over 100 families in the world.

An arachnologist takes years of concentrated study to learn how to identify spiders.  They are identified by structure, not by markings.

The determining features involved are:

1) Arrangement of eyes

2) Number of claws

3) Location and arrangement of certain specialized hairs and spines

4) Structure and arrangement of the spinnerets (silk spinning organs at the rear end)

5) Other characters that you cannot see with the naked eye Species are separated mostly by the fine structure of the sex organs, which can only be seen with high magnification under a microscope.

Very few entomologists and physicians are also arachnologists. This helps to explain how doctor’s misdiagnosis spider bites. House spiders are usually not the same species as the yard or garden spiders outside the house. House spiders are adapted for indoor conditions. So when you are saving a spider by putting them outside, you are more than likely killing him. Spiders found in your bathtub did not arrive there via the drain.

Think about it, drains contain a liquid-filled sediment trap through which spiders cannot penetrate. They end up in bathtubs and sinks because they are looking for water. The probable way they reached the tub or sink is by crawling down your wall. Once in the tub or sink, they are trapped because the slick sides prevent them from escaping. Spiders are not bloodsuckers; they prey on insects and other small creatures.

They have no reason to bite humans, unless provoked. Spiders are the ones who usually suffer. Very few species have venom that can harm humans, dogs, or cats. Spiders, whose venom happens to be more toxic to us, are no more likely to bite us on that account; they are unaware of our existence. Webs are used for catching prey by about half of the spiders species, the remainder of them are either active hunters or some of them will sit and wait for their prey.

A set of images of a horrid injury to a thumb has been circulating since June 2003. These identical pictures surface over and over again, but with different details attached…like what kind of spider bite and where the bite occurred: supposedly ‘brown recluse’ spider bite (military base in Missouri, Wisconsin, Texas, Montana,Ohio, California, Alberta Canada, Costa Rica) supposedly ‘hobo’ spider bite in British Columbia supposedly ‘African’ spider bite in Belgium supposedly ‘solpugid’ bite on an American soldier in Iraq A word to the wise…be very suspicious about what you are reading on the internet, you have no idea what is true and what is not.

Don’t believe it because ‘it is written’…Question by whom and what are their credentials. These photos have been known to be used as PowerPoint presentations in paramedic classes, which spread misinformation rather than educating people.

Other factors to question are:

1) Where did the bite occur?

2) Was a spider caught in the act of biting?

3) Was a spider at the scene of the crime?

4) Was the victim tested for additional etiologic agents of necrosis such as bacterial infection?

5) Did a doctor actually make the diagnosis or was it a self-diagnosis from the victim?

6) Did the diagnosis come from an area of the country that actually has brown recluses?

In our educational class it was explained to us that the diagnosis of ‘brown recluse’ spider bites in Western Washington is incorrect due to the fact that the brown recluse CANNOT exist in our environment, even if they were imported from another part of our country.

Doctors misdiagnose the brown recluse because they see the puncture wound, look it up in their medical books and compare pictures of wounds by spiders and deduce that it was a ‘brown recluse’. The puncture wound is NOT a determining factor.

RODNEY L CRAWFORD University of Washington, College of Arts & Sciences MYTHS ABOUT IDENTIFING SPIDERS

MYTH 1: I found a photo of a spider species that looks just like the spiders in my house, so now I know what they are.

Fact: In other words, you have one color picture of one species of spider, and this magically enables you to tell how that species differs from hundreds of others of which you do not have pictures?

Sorry, but it doesn't work that way. In the first place, as noted elsewhere, naked-eye appearance is more deceptive than useful, in spider identification, to anyone but an experienced specialist. Furthermore, the appearance of one specimen of one species will give you no information on the differences between that species and similar ones, and no idea of how variable the species in question might be.

The geographic range of the species must also be considered. Even if your spider from Texas "looks just like" a photo from Belgium, the chances are that you have not made a correct identification. No spider can be considered reliably identified unless a spider specialist has examined it under a microscope. Not even if it's identical to that photo you found, right down to the very last spot!

MYTH 2: Physicians, exterminators, and entomologists can identify spiders.

Fact: Only arachnologists have the highly specialized skills needed to identify spiders, which take years of concentrated study to learn.

To be sure, a few entomologists (insect specialists) and a very small number of physicians are also arachnologists, but the vast majority are not. No medical school teaches even the basics of real spider identification; the most that medical students are likely to get is misinformation about identification by so-called "markings". Sad to say, numerous physicians have misdiagnosed patients with mysterious sores, without even seeing a spider, as having been bitten by spider species which did not even exist in their locations. Most pest control operators have very inadequate training even in the identification of common pest insects; few are trained entomologists, and I know of only one in the United States who is an arachnologist. Misidentifications by non-arachnologists are the source of a very large number of false spider reports and "scares" in the news media.

MYTH 3: Spiders are easy to identify.

Fact: No such luck! Laypersons often assume that there are only a few spider species around, and all they'd need to identify them would be a few pictures.

In reality, the world holds over 50,000 species of spiders classified into over 100 families. In your local area, there are likely at least 30 families and a few hundred species. Even identifying a spider to family is no trivial task; all the many published keys to spider families are so organized that a beginner will go wrong about half the time. At species level, one needs an expensive microscope, a library of hundreds of separate books, monographs and articles, and a few years of experience to understand the many microscopic details that identify a spider, their similarities, differences, and variation.

MYTH 4: Spider species are distinguished and identified by "markings."

Fact: No, they're not. Spiders do not come color-coded for our benefit.

Imagine trying to identify the make and model of a the color! Spiders are identified by structure. They are classified into families by the arrangement of the eyes (see above), number of claws, location and arrangement of certain specialized hairs and spines (see above), structure and arrangement of the spinnerets (silk spinning organs at rear end), and other characters that you cannot see with the naked eye.

Within families, species are separated mostly by the fine structure of the sex organs (yes, really, I'm not kidding! see below), which can't be seen without high magnification. Color patterns can be very variable within species, and very similar between different species.

For example, the majority of all spider species can be seen as having a "violin" shape somewhere on their bodies; thousands of species have a pattern of "chevrons" on the abdomen. These and other pattern features do not indicate any particular species, and are not signs of danger to humans.

There are exceptions to this rule; a very small number of species do have distinctive pattern elements; but in general, to recognize a spider by naked-eye appearance one must first know all, or almost all, the hundreds of species that live in your locality, their similarities, differences, and variability. Even then, you must usually have a microscope to do more than guess at the spider's identity.


MYTH 1: Spiders come into houses in the fall to get out of the cold.

Fact: This seemingly simple idea conceals many false assumptions.

In reality, house spiders are usually not the same species as the yard or garden spiders outside the house. House spiders belong to a small number of species specially adapted for indoor conditions (constant climate, poor food supply, very poor water supply).

Some house spider species have been living indoors at least since the days of the Roman Empire, and are seldom to be found outside, even in their native countries (usually Europe). Many of these species now live in houses worldwide, and most have been carried by commerce to more than one continent. House spiders colonize new houses by egg sacs carried on furniture, building materials and so forth.

They usually spend their entire life cycle in, on or under their native building. If a large number appear at a specific season, it is usually late summer (August and September) -- not a notably cold time of year! -- rather than fall, and their appearance coincides with the mating season of the given species.

What you are seeing is sexually mature males wandering in search of mates. The females and young remain hidden for the most part, in crawlspaces, storage areas and other neglected rooms; wall and floor voids; behind furniture and appliances, etc. Generally fewer than 5% of the spiders you see indoors have ever been outdoors.

MYTH 2: "I'm very kind to spiders; when I find one in the house, I put it back outside instead of killing it."

Fact: You can't put something "back" outside which was never outside in the first place.

Although some house spider species can survive outdoors, most don't do well there, and some (which are native to other climates) will perish rather quickly when removed from the protective indoor habitat. You're not doing them a favor. In any case, house spiders are mostly harmless and beneficial. Human property rights mean nothing to other species. There was spider habitat for millions of years where your home is now. My advice is, "just wave as they go by."

MYTH 3: Spiders found in bathtubs or sinks have come up through the drains from the sewers.

Fact: This myth goes together with the “coming in from the cold" one, and shows how very reluctant people are to confront the idea that the spiders in their house live there all the time.

I don't know of even one case where a spider was actually shown to migrate into a house through plumbing; modern drains contain a liquid-filled sediment trap through which spiders cannot penetrate.

House spiders are thirsty creatures living in a very water-poor environment, and any that venture near a sink or tub with drops of water in it will try to reach the water, often by climbing down a wall. Once in the slick-sided porcelain basin, they are unable to climb back out unless a helpful human "lends them a hand."

MYTH 4: Spiders in the home are a danger to children and pets.

Fact: House spiders prey on insects and other small creatures.

They are not bloodsuckers, and have no reason to bite a human or any other animal too large for them to eat. In any interaction between spiders and larger creatures like humans, the spiders are almost always the ones to suffer. It is so rare for spiders to bite humans that in a 30-year career of handling tens of thousands of live spiders, I personally have been bitten twice. Both bites had only trivial effects.

A person who is not an arachnologist would not likely be bitten more than once or twice in a lifetime. (“Mystery bites” which people thoughtlessly blame on spiders, don't count! There are no invisible spiders...). Very, very few spider species have venom that can harm humans, dogs, or cats. In most parts of the world, no spiders with medically significant venom have much chance of being found in houses.

In the few areas that are an exception to this rule, the harmless house spider species still greatly outnumber the more toxic ones. And spiders whose venom happens to be more toxic to us, are no more likely to bite us on that account; they are unaware of our existence. Why, why do people waste their time worrying about spiders? It is not spiders that are dangerous to your children; the dangerous ones are other humans!

MYTH 5: Spiders are insects.

Fact: Actually, not everyone believes this.

Around half of my callers did learn in school that spiders are not insects, but I find it rather appalling that the percentage is not higher. And how often, in mass media, we read or hear a phrase like "spiders prey on other insects!" Anyway, spiders belong to the Class Arachnida, insects to the Class Insecta. Arachnids are as distant from insects, as birds are from fish. It really is not a trivial distinction!

Spiders have 2 body parts, 8 simple eyes, no antennae Insects have 3 body parts, 2 compound eyes, 2 antennae, 4 pairs of legs abdomen unsegmented Fact: Technically, a web is a silk structure made to catch prey. Only about half of the known spider species catch prey by means of webs.

Others (shown above) actively hunt for prey (including members of the wolf spider, jumping spider, ground spider, sac spider, lynx spider, and other spider families) or sit and wait for prey to come to them (trap door spiders, crab spiders, and others). Hunting spiders use their silk for the drag line (the single thread all spiders leave behind them when they walk), the egg sac, and in some species, the retreat (a little silk "house" the spider rests in), all shown below, but do not make true webs.

MYTH 6: Any spider species can be found anywhere.

Fact: Except for a few of the house-spider species, most spiders have strictly limited ranges; perhaps a large part of one continent (almost never an entire continent), perhaps only a few states or provinces, or even more restricted.

Each locality has its own spider fauna, its own set of species to choose from in making an identification.


Courtesy of Washington State University Extension

Spiders -- Who's Biting You?

Spider Myths