A Metaltella simoni Spider, imported from South America, in Arlington Texas

This article by Jerry Cates and Jess, first published on 21 February 2010, was last revised on 23 April 2016. © Bugsinthenews Vol. 11:02(10).


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The following email was received from Jess, Arlington TX, on the morning of 9 February 2010:

Jerry–We live in Central Arlington, and have a LOT of these spiders in our home. This is the best quality picture I was able to get with my camera. They are generally between ½” and ¾” in diameter, no bigger. But there are a lot of them, I kill at least 2 a day. Any idea what they are and if they are dangerous?

Unidentified house spider: Jess, Arlington TX, 020910

Unidentified house spider: Jess, Arlington TX — 09 Feb 2010

This is an interesting spider. It has eight eyes, four in each of the two anterior and posterior eye rows, which alone rules out the brown recluse. Its gross body anatomy, including that of the pars cephalica, is nothing like that of a black widow. Those two are the only generally-accepted “dangerous” spiders found in Texas, though a third, the yellow sac spider (Cheiracanthium spp.), is thought by some to pose dangers similar to those of the brown recluse, while many others disagree (though nobody disputes its bite is painful).

By ruling out the first two, I could tell Jess immediately that it probably wasn’t anything to worry about. But what if it is a yellow sac spider? It happens that two species in the genus  Cheiracanthium are found in North America, and both enjoy a wide distribution.  Further, the eyes of these spiders are similar to the eyes we see in our present specimen (two rows of four). The legs are also similar, as are their habits, as they are often found in homes, infesting them as nocturnal wandering hunters, much the way brown recluse spiders do.

However, while Cheiracanthium chelicerae are stout, they are not robustly elongated as with our specimen. Additionally, Cheiracanthium’s spinnerets project posteriorly beyond the abdomen when the spider is viewed dorsally, and our specimen shows no signs of spinnerets. I therefore feel somewhat confident that this is not a yellow sac spider. Of course, I don’t shrink from making mistakes, but one should never be reckless in that regard.

Several gross anatomical features caused me to make a tentative identification for this specimen as Azilia affinis. That conclusion was disputed on 10 October 2011 by Zack Lemann, with the Audubon Institute, New Orleans, LA.

By coincidence I had studied one much like this specimen, under the microscope, just a few days prior to Jess’s email. In September of 2009 a home in Newark, TX was found to be infested with brown recluse spiders. Beginning that month I made monthly visits there, as part of an IRIM P.A.™ program, to apply habitat modification (pest avoidance) techniques as a means of resolving the infestation without using pesticides. As in all the previous cases where I or the homeowner used such measures, the program was a success. On the fourth month of the program the glue monitors ceased to have brown recluse spiders in them, so the program appears to be working.

However, a  few other spiders, some with long chelicerae like this specimen,  do get caught from time to time. When those spiders were viewed from above, under the microscope, their chelicerae showed just like this one, seemingly projecting outward from the face like the chelicerae of a mygalomorph. Of course, under the microscope their distal tips were never in focus when the clypeus was, so the mind could not be tricked by even a casual inspection. In this photograph, made in good lighting that produced a greater depth of field, the illusion is harder to avoid. I hasten to add, however, that although the chelicerae seem to project outward from the face, they are nothing like the chelicerae of a mygalomorph. The latter have chelicerae that, when viewed dorsally, appear as the toe of a boot, not like the wings of a butterfly as these do.

Unidentified house spider, Head & Palps: Jess, Arlington TX 020910

Unidentified house spider, head & palps, line dwg: Jess, Arlington, TX 020910

The line drawing of the head and palps makes it easier to see the positioning of the eyes. It seems clear that both the lateral eyes and the posterior median eyes are separated by more than a single eye diameter, but it is wise to be cautious when analyzing a less than ideal photograph like this one. It is possible that these eyes are closer together than can be discerned. To be certain, one would need to have the preserved specimen available to study under magnification.

Ideally there would be additional information available in the literature to tell us more about this species, so that additional tests could be made using this photograph. Alas, that is not the case. It happens that Azilia affinis is one of those spiders about which not much has been written of late, so I went with what I had and pronounced it, tentatively, a male of that species.

The enlarged emboli in the distal palps give the sex away, as females have no such emboli on their distal palps. It would help if we knew how the emboli appear in all three dimensions; we are at a disadvantage with this single photograph, as the emboli show as simple clubs when, no doubt, their ventral aspects, which are not shown, most likely show important structural details that might point us in another direction.

Many thanks to Zack for informing me of his strong doubts. He kindly provided me with photos of Azilia affinis, which will soon be posted. In the meantime, though I had hoped to visit Jess (or send several vials of alcohol for collection purposes) and thereby try to obtain several specimens of this spider that, when examined in the lab under magnification, would make it possible to arrive at a firmer conclusion regarding its identity, circumstances made that impossible. When making arrangements for that visit, Jess informed me she had employed an exterminator to thoroughly treat her home’s interior for spider control, and that she had not seen any more of these spiders afterward.

My best guess, at present, is based on the fact that this spider appears to have many of the characters of a spider in the Amphinectidae family, Metaltella simoni, a species in the Amphinectidae family. This family was first described by Forster & Wilton in 1973. The genus Metaltella was first described by Mello-Leitão, in 1931, and the species simoni was first described by the German arachnologist Eugen von Keyserling in 1878. It is native to temperate South America, but in the 1940’s was introduced into ports along the Gulf Coast of the United States, arriving via freight from docks in South America. From these introductions it spread along the Gulf Coast from Florida to Texas, and later was also introduced into California via freight shipments arriving there from South America.

This spider is not considered dangerous, though it will bite if handled roughly. It has a tendency to collect in homes, producing rather large numbers of spiders that can be annoying and, for those with arachnophobia, scary encounters. The spider is easily controlled using methods described on a web page I’ve written that is devoted to Spider Extermination and Control.



 Questions? Corrections? Comments? BUG ME RIGHT NOW! Feel free to e-mail jerry.cates@entomobiotics.com. You may also leave a comment in the space provided below.


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