Notes on Brown Recluse Spider Behavior 2

— BugsInTheNews is a VIEWER-PARTICIPANT WEBSITE. This article by Jerry Cates, first published on 2 January 2011, was revised last on 7 July 2012. © Bugsinthenews Vol. 12:01(02)

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Related Links:

• Brown recluse Anatomy
• Brown recluse encounters in Austin, Texas
• Brown recluse encounter in Wichita Falls, Texas
• Brown recluse encounter near Lake Travis, Texas
• Brown recluse encounter in Collin County, Texas

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Sicariidae: Brown Recluse Spider (Loxosceles reclusa); Male on painted cinderblock wall, dorsolateral view; at Home of Jane T., Joplin, MO--Photographed on 15 Oct 2010

Sicariidae: Brown Recluse Spider (Loxosceles reclusa); Dorsal view of male on wall; at Home of Jane T., Joplin, MO--Photographed 15 Oct 2010

Brown recluse behavior:

Most of the photos used in this article were taken during inspection and collection visits to locations in Joplin Missouri,  Grove Oklahoma, and various locations in Collin, Hays, Parker, Tarrant, Travis, and Wise Counties, within the state of Texas.

Note that the spider depicted in the above photos is positioned on the vertical surface of a painted cinder block wall. As the wide-angle photo below confirms, the spider was actually positioned near the ceiling, presumably having climbed there from the floor, below.

This is a very interesting phenomenon, given that one of the anatomical features of recluse spiders is the absence of scopulae on their feet. Scopulae enable spiders to scale smooth vertical surfaces; spiders bereft of these structures are at a significant disadvantage when placed in containers with smooth, vertical, or near-vertical sides. That is one reason why brown recluse spiders are often found trapped in kitchen pots and pans, and in glass or ceramic jars, bowls, and similar kitchenware. Once they fall in, they cannot climb back out.

However, though these spiders cannot scale perfectly smooth vertical surfaces, they are equipped with a pair of sharp, multi-pronged claws on the tips of each foot (tarsus) that provide the spider with remarkable climbing faculties on surfaces that claws can dig into. Brown recluse spiders use skills analogous to those that mountain climbers employ when attacking a sheer mountain face with well practiced fingers and toes trained to find and grip the smallest mountain ledge or socket. Notice in the photo directly below how the claws of the spider’s right leg IV appear to have a firm grip on the partially pliable painted surface of the cinder block wall. The tarsal claws of the brown recluse enable it to obtain a purchase on surfaces that are provided with no more than the faintest of indentations.

This same specimen later used its claws to scale partially up the smooth vertical plastic surface of a laboratory enclosure, simply by gripping the thin edge of a barely discernible mold seam, as discussed below. A note of warning is in order, therefore, for those arachnologists who might presume from a spider’s lack of scopulae that they can safely be kept in ordinary plastic enclosures with vertical sides…

Some people with brown recluse spider infestations are all too  aware that their homes and apartments are infested. However, many if not most who have brown recluse infestations are unaware they are sharing their abodes with these spiders.

Among those who do know, many are reluctant to admit it. Most are acquainted with the common presumption that brown recluse spiders only infest cluttered, unkempt homes. Thus, admitting you have brown recluse spiders is supposedly tacit admission that your home is not very clean. Never mind that this presumption is false; my experiences have proved that the brown recluse spider are often found — often in large quantities — within some of the cleanest homes in the U.S.

Sicariidae: brown recluse (Loxosceles reclusa); Closeup of RL4 claw gripping painted cinderblock wall; Home of Jane T., Joplin, MO--photographed on 15 Oct 2010

Sicariidae: brown recluse (Loxosceles reclusa); Male specimen high on painted cinderblock wall at home of Jane T., Joplin, MO--photographed on 15 Oct 2010

Few of those with brown recluse infestations understand the real reasons why their homes are infested, where these spiders are likely to  congregate, or what they feed on, much less how many of spiders might be involved.

This lack of knowledge is not limited to members of the general public. Many licensed pest management professionals, including those who service clients in areas where brown recluse spiders are common, have only a surface knowledge of brown recluse spider biology. My own particular case is an excellent example: I serviced a large number of nursing homes, hospitals, and medical clinics all over Texas for over 25 years without ever finding a single brown recluse spider. Only over the past few years have my travels crossed paths with this arachnid, though now — as an active investigator into brown recluse anatomy, habitat, and behavior — my encounters with this spider occur quite often, in very unlikely places.

According to one investigator (Sandidge, 2009) many pest management companies tackle brown recluse infestations with little or no training and without testing the pesticides they use.

They also tend to rely on information from outdated publications and from misleading, inaccurate sources, many of them acquired via Internet searches.

As mentioned earlier, when the brown recluse spider–collected on 15 oct 2010 from the wall of Jane T.’s home in Joplin Missouri–was brought to the EntomoBiotics Inc. laboratory, it was placed in a spacious plastic enclosure. This rectangular enclosure had 12-inch high, smooth, vertical walls. Four days later it was observed to have climbed nearly three inches up the side of one of the enclosure’s seemingly smooth walls (see the photo below). On closer examination, it became clear that a horizontal mold seam in the plastic surface of each wall, some 2.5 inches above the floor of the enclosure, provided a lip that the spider’s claws could attach to (as shown in the accompanying photograph).

Inasmuch as there were no other mold seams in this particular enclosure’s walls, the risk that the spider might extricate itself from the enclosure by its claws was low to nonexistent. Later observations proved that out, as the spider never succeeded in extending its reach beyond the mold seam shown in these photos.

What this observation pointed out, though, was how persistent and facile these spiders are. In order to reach the lip of the mold seam it was necessary for the spider to stretch its legs as far as possible, while palpating the enclosure wall for anything it could attach to. This exercise would have taken a considerable amount of time, and a modicum of energy, to achieve success. However, that initial success could not be capitalized upon, as no other seams could be found higher up the enclosure wall.

Sicariidae: brown recluse (Loxosceles reclusa); closeup of tarsal claw of right leg IV of male specimen, collected on 15 October 2010 at home of Jane T., Joplin, MO, gripping mold seam of plastic enclosure at EntomoBiotics Lab--photographed on 19 Oct 2010

Sicariidae: brown recluse (Loxosceles reclusa); closeup of male specimen, collected on 15 October 2010 at home of Jane T., Joplin, MO, scaling vertical wall of plastic enclosure at EntomoBiotics Lab--photographed on 19 Oct 2010

Dr. Sandidge went on to say that most pest management companies use unnecessarily expensive equipment to control brown recluse spiders.

His experience has shown that the use of power sprayers, power dusters, and fogging machines, leads to excessive applications of pesticides. Additionally, he points out that companies that rely on such equipment typically fail to achieve control of the brown recluse spider infestations they are after. Not only are those pesticides not helpful, says Dr. Sandidge, but sometimes they end up making a bad situation worse.

To paraphrase Sandidge’s comments, it is more effective to use a lot of knowledge with a modicum of toxicants, than the other way around.

My observations, though based on experiences that are much less extensive than those of Dr. Sandidge, substantiate his views in almost every particular. However, rather than simply limiting the use of pesticides to control brown recluse spiders, I prefer avoiding pesticides altogether in favor of a completely non-toxic approach. The PestAvoidance concept developed and expanded at EntomoBiotics Inc.  emphasizes habitat modification products and techniques to produce an environment that neither nurtures nor attracts pests. Tests conducted in homes infested with brown recluse spiders indicate that program works as effectively on them as it does with other pests.

One of the homes in which I recently collected  a number of brown recluse specimens turned out to be one of the most immaculate, well-cared-for homes I’ve seen. The homeowner, in fact, is one of those people who cannot stand clutter. Furthermore, she has lived in this home for over twenty years. So much for the mythical cluttered, unkempt abode these spiders are generally believed to prefer.

The first two photos posted, above, are of a male brown recluse spider on the wall of the downstairs living/recreation area of her clean, beautiful, elegantly appointed home.

Sicariidae: brown recluse (Loxosceles reclusa); Examining Specimen Removed from Hot Tub Drain; Home of Jane T., Joplin, MO--15 Oct 2010

Sicariidae: brown recluse (Loxosceles reclusa); webbing in hot tub drain at home of Jane T., Joplin, MO--photographed on 15 Oct 2010

Though the owner, along with me and my wife, searched that home diligently for brown recluse spiders, none of us noticed the (rather conspicuous) spider on the wall until the inspection was nearly complete. We had each passed by that location several times. Perhaps it was because the wall was in a darkened corner of the room. Maybe it was the fact that the spider kept very still, without moving a hair (not hard to do, since the brown recluse is — in comparison with most other spiders, excepting the small hairs adorning each leg — essentially hairless), as though it was fast asleep.

Once we noticed it, we took a series of photos, sometimes merely a few inches from the spider. Still, the spider didn’t move a muscle. That enabled me to carefully place a collection vial over it, so it could be trapped unharmed. In an instant the spider came alive, scurrying around in the collection vial, searching frantically for an avenue of escape.

One interesting find in this home was that two brown recluse spiders had taken up residence in the open drain of a floor-level hot tub that had not been used for several months (see the photos directly above, and below). Here we witnessed a classical rendition of  the brown recluse blues: “I’ve fallen (in), and I can’t get (out)”. Out of the hot tub, that is. The spiders were able to enter and exit the drain with ease; they just couldn’t scale the smooth walls of the tub itself.

But, at least until I happened by, the plight of these spiders wasn’t all that bad. Though unable to leave the bowl of the hot tub, they managed to survive. Many kinds of crawling bugs cannot get out of such places, either, so the captive spiders were practically guaranteed a good meal from time to time. All they needed was patience, and a low metabolic rate. Which brings up another point about brown recluse biology: their atypically low heart and metabolic rates, coupled with a few other anatomical traits (e.g., an ability to conserve moisture loss), enable them to survive for long periods with little or no food or water.

Student arachnologists with even a brief acquaintance with brown recluse biology know to expect such experiences. Brown recluse spiders are prone to behaving this way. When at rest they often revert to a trance-like state, remaining in the same place, with their limbs frozen in a characteristic slanted posture, for hours–even days–at a time.

Sicariidae: brown recluse (Loxosceles reclusa); Closeup of webbing in hot tub drain; at Home of Jane T., Joplin, MO--Photographed 15 Oct 2010

Sicariidae: brown recluse (Loxosceles reclusa); dorsal view of corpus of male scaling plastic enclosure at EntomoBiotics Lab; collected on 15 Oct 2010 at Home of Jane T., Joplin, MO--Photograpshed on 19 Oct 2010

There is more to this pattern of behavior than meets the eye.

Although the heart rates of most spiders are negatively correlated with body weight, one study (Carrel et al., 1976) determined that brown recluse spiders–which have unusually low body weights–also have among the slowest heart rates of any spiders.

In fact, their heart rates, along with those of their close relatives, the spitting spiders (Scytodidae), were found to be comparable to those of mygalomorph tarantulas, which are some of the largest spiders known.

Carrel concluded that recluse and spitting spiders, being near-sighted ambush hunters, feed only occasionally and prefer to feed on prey that they do not have to forcefully subdue.

As we searched this home for evidence of brown recluse spiders, we eventually arrived at the interior hot tub mentioned above.

It was a floor-level tub, with a central drain, and had not recently been used.

A quick look in the drain revealed a crude web of silk, and what appeared to be one or two live spiders.

Sicariidae: Brown Recluse Spider (Loxosceles reclusa); Closeup of pars cephalica, showing dorsal pubescence; Collected on 101510 at Home of Jane T., Joplin, MO--Photographed 08 Dec 2010

Sicariidae: Brown Recluse Spider (Loxosceles reclusa); Closeup of pars cephalica, showing eye details; Collected on 101510 at Home of Jane T., Joplin, MO--Photographed 08 Dec 2010

The photos of the drain, above, show these spiders (look for the long, spindly legs), but you have to look hard for them. Using a forceps to dismantle the webbing, it was possible to retrieve both spiders–excellent brown recluse specimens–to add to my collection.

More to come…

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References:

• Carrel, James E., and R.D. Heathcote, 1976. Heart Rate in Spiders: Influence of Body Size and Foraging Energetics. Science, 193: 148-150.
• Cramer, Kenneth L., 2008. Are Brown Recluse Spiders, Loxosceles reclusa (Araneae, Sicariidae) scavengers? The influence of predator satiation, prey size, and prey quality. J. Arachnology 36:140-144.
• Cramer, Kenneth L., Alex V. Maywright, 2008. Cold temperature tolerance and distribution of the brown recluse spider Loxosceles reclusa (Araneae, Sicariidae) in Illinois. J. Arachnology 36:136-139.
• Gertsch, Willis J. 1958. The Spider Genus Loxosceles in North America, Central America, and the West Indies. AMNH Novitates 1907: 1-46.
• Gertsch, Willis J., Franklin Ennik, 1983. The Spider Genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae). Bull. AMNH 175: 254-360.
• Guarisco, Hank, 1999. House Spiders of Kansas. J. Arachnology 27:217-221.
• Hogan, Christopher J., Katie C. Barbaro, Ken Winkel, 2004. Loxoscelism: Old Obstacles, New Directions. J. Annemergmed 08: 608-624.
• Parks, Jennifer, William V. Stoecker, Charles Kristensen, 2006. Observations on Loxosceles reclusa (Araneae, Sicariidae) feeding on short-horned grasshoppers. J. Arachnology 34:221-226.
• Sandidge, Jamél S., 2009. Brown Recluse Spiders: A knowledge based guide to control and elimination. Pubkished by BRS Pest Control, McLouth, KS.
• Ubick, D., P. Paquin, P.E. Cusing and V. Roth, editors, 2005. Spiders of North America. Published by the American Arachnological Society.
• Vetter, Richard S., 2008. Spiders of the genus Loxosceles (Araneae, Sicariidae): a review of biological, medical and psychological aspects regarding envenomation. J. Arachnology 36:150-163.

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