The maligned brown recluse and other spider misconceptions

brown recluseIrene Shonle, Director CSU Extension in Gilpin County.  There are few critters out there that inspire as much fear as spiders – the brown recluse spider in particular. The internet and news stories lead us to believe that there are thousands of people who are bitten each year, and that each bite turns into a huge necrotic wound that requires hospital stays and sometimes amputation.

I have two pieces of good news for everyone: first, there are no brown recluse spiders in Colorado. (Please see the distribution of the spider in the accompanying photo.) In very rare cases, they can be brought into the State in moving boxes, but there are no reported cases of them becoming established here.

Then why are there so many reports of brown recluses? Turns out we’re lousy at spider identification. In 2005, arachnologist Rick Vetter examined 1,773 specimens of suspected brown recluses submitted by the general public. Less than 20 percent — 324 — were brown recluses. All of the actual brown recluses were submitted from Arkansas, Missouri, Kansas, Oklahoma, the western portions of Tennessee and Kentucky, the southern parts of Indiana and Illinois, and the northeastern parts of Texas. No spiders from the other states were brown recluses, confirming this distribution.

The second bit of good news is that even if you were to be bitten by a brown recluse when you were visiting family in one of those states, only 10% of the bites lead to necrotic lesions. So why are people from Colorado being told they were bitten by a brown recluse? Turns out that many authorities, including poison control centers and physicians, aren’t much better at identifying the brown recluse, so even if a necrotic lesion is diagnosed as being a brown recluse bite, it probably isn’t. What may be happening is the diagnosis of a brown recluse bite has become a popular catch-all for situations where the cause of a skin lesion can’t be easily identified. Other possible causes are bacterial, viral and fungal infections; poison oak and poison ivy; thermal burns, chemical burns; bad reactions to blood thinners and even herpes.

Another spider myth is that ‘the daddy longlegs has the world’s most powerful venom, but its jaws (fangs) are so small that it can’t bite you’. This persistent urban legend has no basis in fact. Two different, unrelated species are called “daddy longlegs.” Harvestmen, what we usually call daddy long legs around here, have no venom of any kind (and is actually not a spider). Pholcid spiders (cellar spiders) do have venom, but it is quite weak.

Another myth is that spiders found in bathtubs or sinks have come up through the drains from the sewers. In reality, modern drains contain a liquid-filled sediment trap through which spiders cannot swim. House spiders crawl down walls to sinks or tubs with drops of water to get a drink. Once in the slick-sided porcelain basin, they are unable to climb back out unless a helpful human lends them a hand.

Finally, a reminder that spiders are beneficial insects, despite the fear they may provoke. They keep down populations of insect pests both in the home and in the yard. Most spiders are shy and will avoid humans. Very, very few spider species have venom that can harm humans, dogs, or cats, and in the rare cases where spiders do bite, most only cause a mild irritation. Consider allowing spiders to live and do their thing in peace.

The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, Colorado State University Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. Colorado State University Extension is dedicated to serving all people on an equal and nondiscriminatory basis.