Fun spider facts PMPs need to know

Cobweb spiders were found in 100% of homes in a recent
survey in North Carolina.  

Last year an article was published by Matthew Bertone and colleagues at North Carolina State University about arthropods found in homes.  The only organism found in 100% of the homes and over 90% of the basements surveyed was spiders.  The only other organisms that came close were flies and ants and carpet beetles.  By contrast, German cockroaches were found in only 6% of homes and fleas in 10% of homes.

What this tells me is that everyone in pest control needs to know something about spiders.  So here are some fun spider facts that you can impress your family and friends with.

• Spiders consume an estimated 400-800 million tons of prey every year, at least as much meat as all 7 billion humans on the planet (400 million tons of meat and fish annually).
• The world spider population weighs 29 million tons, as much as 478 Titanics.
• Most spiders kill and eat prey in forest and grasslands (95%) and only 2% of annual spider prey are eaten in agricultural lands, probably because of the regular disturbances caused by farming activities.
• Spiders have been around about 400 million years, longer than all but perhaps the earliest insects.
• Over 45,000 different species of spiders have been described by science.  Only about 3,800 species are known from the U.S. and Canada.
• Half of the different species of spiders in the U.S. are less than 3 mm (1/8 inch).
• Spiders disperse largely by parachuting or "ballooning".  Young spiderlings produce lightweight strands of silk to catch updrafts, especially on sunny mornings. 
• Some spiders have been captured ballooning at altitudes up to 2.5 miles, over 13,000 feet.  It's thought that electrostatic forces assist with flight.
• Spiders feed exclusively on liquids.  They lack jaws to chew food.
• Although nearly all spiders likely have venom, only a handful are capable of causing bites that are medically important to humans.  These include the widow and recluse spiders in the U.S.
• If you ever find yourself walking into an orb-shaped spiderweb, relax.  None of the orb weaver spiders are considered dangerous to humans (For you Hobbit and Lord of the Ring fans, Shelob was more likely a cobweb spider, not an orb weaver).

This post was inspired by a recent Washington Post article by Christopher Ingraham. The fun facts were gleaned from several sources, including the Bertone et al. paper which provided estimates about spider eating capacity; a National Geographic post by Liz Langley;  Evolution of the Insects by Grimaldi and Engel; and Common Spiders of North America by Richard Bradley.  As a handy reference for the common spiders, I heartily recommend the wonderful little book Spiders and Their Kin by Levi and Levi.  

One less pest to worry about...the hobo spider

This news is not something you are going to find anywhere else on the Internet. Rather it concerns something you will no longer find on the Internet.

Recently the Centers for Disease Control quietly removed hobo spider from its website on venomous spiders.  This goes back to a story previously blogged about on Insects in the City, namely that there appears to be no verified scientific evidence that hobo spider as a cause of necrotic bites in humans. Nevertheless, until now, the CDC continued to list hobo spider as a cause of venomous bites on its website.

The hobo spider (Eratigena agrestis) is a common house
spider in Europe, where there is no history of
human envenomization.

According to Colorado State University Extension entomologist, Whitney Cranshaw, "This is a... long overdue, but very welcome change. A large amount of scientific evidence had accumulated over the past 15 years that utterly refutes the claims of the original 1991 study that purported to make a link between slow healing wounds and the bites of this spider."

According to Cranshaw, over the past year the American Arachnological Society and others have petitioned the CDC to remove hobo spider from its web page.

Sometimes referred to as the aggressive house spider, the hobo spider is a European import that has established itself over the past century in the Pacific Northwest, from Washington to Colorado. Following a flurry of publicity in the early 1990s, it was thought to be an explanation for brown recluse like symptoms sometimes reported from this part of the country, where brown recluse is not found. This information even found its way into some pest control guide books.

Despite fears in the U.S. the spider has no history of association with necrotic bites in Europe, and repeated experimentation in recent years could not replicate skin lesions supposedly associated with its bite.

Cranshaw bemoans the fact that it will still be a long time before all the hobo spider misinformation on the Internet fades, but in the meantime you and your customers can sleep a little easier. There is one less pest to worry about.


For more information

Anyone who wishes to look into this issue in more depth may be interested in this bibliography compiled by Dr. Whitney Cranshaw, Colorado State University, of articles concerning Eratigena agrestis as a medically important spider.

Original articles suggesting Eratigena (formerly known as Tegenaria) agrestis is a medically important species 

• Akre, R. D., and E. A. Myhre. 1991. Biology and medical importance of the aggressive house spider,Tegenaria agrestis, in the Pacific Northwest (Arachinida: Araneae: Agelenidae). Melanderia 47: 1–30. 
• Vest, D. K. 1987a. Necrotic arachnidism in the northwest United States and its probable relationship toTegenaria agrestis (Walckenaer) spiders. Toxicon 25: 175–184. 
• Vest, D. K. 1987b. Short communications envenomation by Tegenaria agrestis (Walckenaer) spiders in rabbits. Toxicon 25: 221–224. 
• Vest, D. K. 1993. Differential diagnoses of necrotic arachnidism in the northwestern United States. Am. Arachnol. Soc. 48: 10 (Abstr.). 
• Vest, D. K. 1996. Necrotic arachnidism-Pacific Northwest, 1988–1996. J. Am. Med. Assoc. 275:1870–1871. 

Articles refuting the purported association of Eratigena (=Tegenaria) agrestis as a source of necrotic arachnidism (skin disfiguring spider bites)

• Binford G.J. 2001. An analysis of geographic and intersexual chemical variation in venoms of the spider Tegenaria agrestis (Agelenidae). Toxicon, 39:955-968. 
• Vetter R.S., Roe A.H., Bennett R.G., et al. 2003. Distribution of the medically-implicated hobo spider (Araneae: Agelenidae) and a benign congener, Tegenaria duellica, in the United States and Canada. Journal of Medical Entomology, 40:159-164. 
• Vetter R.S. 2004. Causes of Necrotic Wounds other than Brown Recluse Spider Bites. University of California Riverside. http://spiders.ucr.edu/necrotic.html. Last accessed August 19, 2011. 
• Vetter R.S. and Isbister G.K. 2004. Do Hobo Spider Bites Cause Dermonecrotic Injuries? Annals of Emergency Medicine. December, 44:6. 
• Melissa M. Gaver-Wainwright, Richard S. Zack, Matthew J. Foradori,3and Laura Corley Lavine. 2011. Misdiagnosis of Spider Bites: Bacterial Associates, Mechanical Pathogen Transfer, and Hemolytic Potential of Venom from the Hobo Spider,Tegenaria agrestis (Araneae: Agelenidae) . Journal of Medical Entomology 48(2):382-388. doi: http://dx.doi.org/10.1603/ME09224 
• Bennett, R. G. 2002. Hyperbole and hysteria on the path to enlightenment: a review of current Tegenaria projects of relevance to Canadian arachnologists. Can. Arachnol. Newsl. 4–10. 
• Bennett, R. G. 2004. An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada. Can. Fain. Physician 50: 1098–1101. 
• Benoit, R., and J. R. Suchard. 2006. Necrotic skin lesions: spider bite—or something else? Consultant 46: 1386–1394. 
• Bettini, S., and P. M. Brignnoli. 1978. Review of the spider families, with notes on the lesser known poisonous forms. In S. Bettinik (ed.), Arthropod Venoms, Handbook of Experimental Pharmacology. Springer-Verlang,Berlin, Germany. 
• Isbister, G. K. 2004. Necrotic arachnidism: the mythology of a modern plague. J. Lancet 364: 549–553. 
• Vetter, R. S., and G. K. Isbister. 2004. Do hobo spider bites cause dermonecrotic injuries? Ann. Emerg. Med. 44: 605– 607. 
• Vetter, R. S., and G. K. Isbister. 2008. Medical aspects of spider bites. Annu. Rev. Entomol. 53: 409–429.

What do socks and bulletproof vests have in common?

Last week Notre Dame and University of Wyoming scientists announced a breakthrough in the commercial mass production of spider silk. 

For years I have heard speakers talk glowingly of spider silk--about its tensile strength that is greater than steel, its amazing ability to stretch, and its ability to retain its strength at temperatures as low as -40 degrees C. It also is thought to possess antimicrobial properties that might make it useful in medicine. Possible uses of spider silk include making superior surgical suture thread, bullet-proof vests, automobile air bags and other strong, lightweight  fabrics that could be used for clothing like running socks and athletic shirts.

Unfortunately, spider silk is amazingly difficult to obtain.  Spiders have been milked, or more properly, "silked"; but this impractical for obtaining all but the smallest quantities of silk.  This is what makes the Notre Dame story interesting.  Molecular biologists have attempted in recent years to product silk through the process of genetic engineering.  One apparently failed biotech venture involved insertion of spider silk genes into goats, that produced silk in their milk.  The idea was that the silk could be extracted from the milk.  Lately researchers have focused on inserting spider silk genes into the all-time best producers of silk, the silkworm caterpillar. The result is a caterpillar that spins a combination of silkworm and spider silk, with improved toughness and elasticity.


All this reminds me of the many times people have asked me, "What good is that bug?"  Spider silk research is just one example of the many amazing products that are possible if we protect, and take the time to learn about our biological heritage.  Who would have guessed that tiny spiders might hold the secret of antibacterial socks, or a better air bag in your car?  And what other useful insects or arthropods are out there, if we just take the time to preserve and study them?  All this becomes especially significant when you consider that hundreds of thousands of insects will likely go extinct over the next 50 years if habitat destruction is not controlled.  The loss to humankind of failing to protect these resources is literally incalculable.