A Male Trapdoor Spider in Cedar Creek, Texas 1

David and Adette have been battling scorpions in their home and yard Recently, they also began seeing a few of these large black spiders, and that was almost as troubling as the scorpions. Until, that is, she learned that they are signs of a healthy lawn.

Background : Adette and her husband own a relatively large ranch in rural Bastrop County, Texas, that is forested with mature oaks, hickories, cedars and pines. Their home is near the center of the ranch, and is over 20 years old. The home itself, and the immediate area around it, were badly infested with striped bark scorpions (Centruroides vittatus) when they moved in last year. A snake skin was also found, suggesting that snakes may be abundant in the area.

Of course, both of these organisms are common inhabitants of the area, so working out a PestAvoidance program, which Adette and her husband have now begun to carry out as a do-it-yourself project, was a good idea. Though the program appears to be working to help them avoid scorpions and snakes, the mode of action for their particular program is such that certain other organisms in the same environment may not be affected. Actually, that’s a good thing, but only so long as the other organisms are not dangerous.

Beginning in the fall of 2009, for example, she noticed a few relatively large, black spiders in her home. They were slow-moving, and not aggressive, so Adette scooped each one up on a piece of cardboard and carried it outside “where it belonged.” I’d surveyed the spiders in their home when they first moved in, and besides some spitting spiders (Scytodidae: Sytodes), and a few wolf spiders (Lycosidae), nothing of significance had been noted. These new ones were a kind of spider she had not seen before. When she called me about them several weeks ago, I asked if she would take some photographs that would help identify them. This e-mail was her reply to that request, delayed by several weeks until she found a suitable specimen to photograph.

The Photograph:  The original image was very dark, and showed few details, so I used image enhancement software to bring out some of the subtle features and created a line drawing that could be annotated.  You may want to click on these images to enlarge them; then just click on the back arrow to return to this post.  I’m used to working with low resolution imagery, and often have to use minimal cue analysis to pull out indistinct features that, when combined, often tell a lot about the identity of the organism. This is one of those cases where using minimal clues is required and–fortunately–produces positive results.

Paraxial Chelicerae: Notice how the mouthparts (chelicerae=jaws) of this spider project outward, from the face, a considerable distance. Look closely and you will see an indistinct line that separates the jaws (chelicerae) into left and right halves. These end, at the face, such that the line of separation is roughly perpendicular to the forward margin of the face (the leading edge of the spider’s clypeus). Common spiders, in the Araneomorphae, have chelicerae that drop sharply downward at the clypeus, rather than projecting outward as with this spider. Thus, it is not an araneomorph, but a mygalomorph, i.e., a member of a group that includes tarantulas and trapdoor spiders.  This is an important point to make early in the identification process, as it narrows the range of candidates considerably.

Hard Shiny Carapace: Now notice that the carapace (the part of the spider between the mouthparts and the abdomen) appears hard, black (or very dark brown), and shiny. That clue comes from the small, but telling glint of light off a portion of its lower left quadrant. It’s another important point. A glabrous (not hairy) carapace that is hard, very dark, and shiny is characteristic of certain mygalomorphs, and does not include the tarantulas. Some tarantulas have a hairless carapace, but the surface is leathery, not hard, dark, and shiny like this one.

Enlarged Distal Pedipalps: Notice next that the pedipalps (two diminutive leg-like appendages extending from the face outward, in front of the spider) are greatly enlarged at their distal ends. See, in particular, how the far ends of these appendages are swollen, while the segments attaching them to the face are slender stalks. This tells us the spider is a male, as the swelling at the end of each pedipalp–and this happens to be true for araneomorph males as well–serves as a sperm reservoir, and is used to physically transfer sperm to the female’s epigynum during mating. The female pedipalp, by comparison, is more like a diminutive leg throughout its length (the distal end is not enlarged).

Projecting Spinnerets: Another characteristic of the mygalomorphs is that, in most cases, their spinnerets project outward, beyond the posterior edge of the abdomen. Notice that is the case with this spider.  Now, some of the araneomorphs have this same anatomical character, most notably the Agelenidae–the funnel-web weavers.  But the agelinids (and all the rest of the araneomorphs) don’t have paraxial chelicerae, so that takes them out of the running.

This spider has stout legs, and if you look at the two legs on the right side at the top of the image, you will see that the last discernible segment, which is actually two segments (the tarsus and metatarsus), joins to the tibia where the proximal end (the end closest to the spider’s body) of the tarsus is noticeably bowed. This is a common feature seen in a number of trapdoor spiders. other important characteristics in the legs that cannot be seen in this photo but that, if we could see them, would tell us more about the species. For example, if the tibiae of legs I and II sport large mid-ventral megaspines, that would place this spider in the genus Eucteniza; though these structures may be present on this specimen, we cannot see them clearly.

But suffice it to say that males of many if not most species of trapdoor spiders are prone to leaving their burrows in search of females following a cold rain. From all indications, this one did just that, but failed to find a mate before the freezing cold air brought its life to an untimely end. The pursuit of a mate carries certain risks, and this fellow went to its reward doing what nature demanded.

North American Mygalomorphs in General: It happens that the mygalomorphs, as a group, are capable of delivering a painful, but medically insignificant bite. Your experience may vary, depending on your particular sensitivity to allergens etc. Any time you are bitten by a venomous critter, you should watch for signs of complications, and if such signs are observed (usually within the first couple of hours), it is important to consult a medical professional immediately. It is unlikely, in any case, that you will even experience a bite from a trapdoor spider. Like the tarantulas that they are closely related to, they only bite if provoked.

Trapdoor Spiders are Beneficial Yard Fauna: Over 120 species of trapdoor spiders have been identified worldwide, where they prey on organisms that are smaller, about their own size, or slightly larger than they are. In North America, these spiders are large enough to prey on fairly large insects, and if you find them in your home or on your patio after a cool rain, that is a good indication that you have a healthy yard. In fact, if you don’t see any trapdoor spiders in those places, your yard may not be as healthy as it should be. It’s easy to make your yard unhealthy. Broadcasting broad-band pesticides, for whatever reason, will often kill these spiders. That’s counter-productive, because trapdoor spiders, along with the wolf spiders in the Lycosidae family (which are also killed en masse when broadcasted pesticides are applied in yards) are very good at killing many of the bugs you are putting pesticides out for. In other words, putting pesticides on your yard usually kills a lot more than “bad” bugs. More often than not, such pesticides also kill the “beneficial” ones, like the trapdoor spiders. That, of course, makes things worse, not better.

Now, what should be done about these spiders? Good question. They are not nearly as prolific as scorpions (they rely on food that drops by, not on actively searching for prey the way scorpions do), so the danger of their populations skyrocketing is rather small. At the density seen in Adette’s yard, they are probably good at preying on scorpions, so their presence would reduce the scorpion population. They attack just about every arthropod — besides their own species — that comes too close to their lairs, so scorpions would be wise to avoid getting too close.  I am inclined, for this reason, to want as many trapdoor spiders in my yard as the yard can support. That means not broadcasting pesticides of any kind, and not extending the use of habitat modifiers (essential oil sprays and granules) beyond the perimeters of yards and structures, by broadcasting them except as part of a habitat modification project carried out to control ticks and fleas.

Adette is one of those special people who has an appreciation for the importance of maintaining a healthy ecosystem in her own yard. Every trapdoor spider she’s found in the house got picked up and taken outside, unharmed. She knows now that these spiders do not pose a risk to her or her family, and actually provide benefits to the yards they live in by preying on insects they encounter there.

The world could use more people like Adette, in my humble opinion…

The following posts feature spiders in the Cyrtaucheniidae family:

• Male Trapdoor Spider; Marvin W., Kempner TX–11.12.2008

• Male Trapdoor spider; Joy R., San Antonio, TX–03.19.2010

• Male Trapdoor spider; Stacey, Austin, TX–01.09.2011

• Euctenizidae (Myrmekiaphila, poss. new species): 2 Male Trapdoor spiders; Dave Peters, Cresson, TX–02.24.2011

• Euctenizidae (Myrmekiaphila neilyoungi): Trapdoor Spider: Jeannette H., Mobile, AL–03.10.2011

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Taxonomy:

• Kingdom Animalia (an-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (1707 – 1778), using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products;
• Phylum Arthropoda (ahr-THROPP-uh-duh) — first described in 1829 by the French zoologist Pierre André Latreille (1762 – 1833), using the two Greek roots αρθρον (AR-thron) = jointed + ποδ (pawd) = foot, in an obvious reference to animals with jointed feet, but in the more narrow context of the invertebrates, which have segmented bodies as well as jointed appendages;
• Subphylum Chelicerata (Kuh-liss-uh-RAH-tah) — first described in 1901 by the German zoologist Richard Heymons (1867 – 1943) using the Greek noun χηλη (KEY-lay) = a claw, talon, or hoof + the Greek noun κερας (SAIR-as) = an animal’s horn + the Latin suffix ata — which by convention is suffixed to the names of animal subdivisions — to refer to animals that have specialized appendages before the mouth that they use in feeding, capturing and securing prey and that — in the case of spiders — are further equipped to inject venom and digestive agents into their prey;
• Class Arachnida (uh-RAKH-nuh-duh) — first described in 1812 by the French naturalist and zoologist Jean Léopold Nicolas Frédéric Cuvier (1769 – 1832), usually referred to as Georges Cuvier, using the Greek noun αραχης (uh-RAH-kes) = a spider, in reference to all eight-legged arthropods, including such disparate animals as ticks, mites, scorpions, harvestmen, solpugids, and spiders;
• Order Araneae (uh-RAY-neh-ee) — first described in 1757 by the Swedish entomologist and arachnologist Carl Alexander Clerck (1709 – 1765), who used the Latin word aranea = a spider or a spider’s web, to refer to eight legged arthropods that spin webs;
• Suborder Opisthothelae (oh-PIS-thoh-THEE-lee) — first described in 1990 by the American arachnologists Richard C. Brusca and Gary J. Brusca, who used the Greek words οπισθεν (oh-PIS-thehn) = behind, at the back, yet to come + θηλη (THEE-lee) = nipple or teat, to distinguish this grouping of spiders from the more primitive spiders in the suborder Mesothelae, in that certain characters (e.g., tergite plates, ganglia in the abdomen, and — in particular, inasmuch as the suborder name is a direct reference thereto — median-positioned spinnerets) of the latter are absent in the former; thus spiders in this suborder have spinnerets positioned at the hindmost portion of the abdomen;
• Infraorder Mygalomorphae (my-GAL-oh-MOHR-fee) — spiders with paraxial chelicerae and two pairs of book lungs, as in the more primitive Mesothelae, but without the latter’s tergite plates and most of the latter’s abdominal ganglia, and having their spinnerets positioned at the abdomen’s hindmost portion rather than mid-ventrally as in the Mesothelae; presently comprised of fifteen families:
  • Atypidae (Thorell 1870) — 3 genera, 49 species (Platnick WSCv13.5); commonly known as purseweb spiders; 8-27 mm, yellow-brown to dark purple-black in color; the legs of male specimens of Sphodros rufipes (Latrielle 1829) and S. fitchi (Gertsch & Platnick 1980) are bright orange-red;
  • Antrodiaetidae (Gertsch 1940) — 2 genera, 33 species (Platnick WSCv13.5); commonly known as foldingdoor, collardoor, or turret spiders (Antrodiaetus), and trapdoor spiders (Aliatypus); 6-26 mm, tan to chestnut brown, with one or more tergites on the anterodorsal abdomen; live in burrows with a flexible collar, a rigid turret, or a trapdoor at the mouth;
  • Mecicobothriidae (Holmberg 1882) — 4 genera, 9 species (Platnick WSCv13.5); no common name; mygalomorphs with two tergites on their anterodorsal abdomen (these sclerotized patches may be fused); build sheet webs with silk tubes from sheet to ground that lead into hiding places under terrestrial objects;
  • Hexathelidae (Simon 1892) — 12 genera, 112 species (Platnick WSCv13.5);
  • Dipluridae (Simon 1889) — 24 genera, 179 species (Platnick WSCv13.5); commonly known as mygalomorph funnelweb spiders; 3.5-17 mm, pale tan to purple-brown in color; thoracic furrow in the form of a short longitudinal groove or a shallow pit or rounded depression;
  • Cyrtaucheniidae (Simon 1889) — 10 genera, 102 species (Platnick WSCv13.5);
  • Ctenizidae (Thorell 1887) — 9 genera, 128 species (Platnick WSCv13.5); no common name; 10-30 mm or more in length, tan, dark chestnut brown, and black in color; the females lack scopulae, but are equipped with a number of robust lateral digging spines on their pedipalps, as well as on the tarsus, metatarsus, and tibia of legs I and II; carapace generally glabrous, with few distinct spines; thoracic furrow is transverse, typically very deep and procurved; burrows are covered with a thick cork-type trapdoor for all genera, except Cyclosmia Ausserer 1871, which have wafer-type trapdoors;
  • Euctenizidae (Raven 1985) — 7 genera, 33 species (Platnick WSCv13.5);
  • Idiopidae (Simon 1889) — 22 genera, 314 species (Platnick WSCv13.5);
  • Actinopodidae (Simon 1892) — 3 genera, 40 species (Platnick WSCv13.5);
  • Migidae (Simon 1889) — 10 genera, 91 species (Platnick WSCv13.5);
  • Nemesiidae (Simon 1889) — 43 genera, 364 species (Platnick WSCv13.5); 16-30 mm, golden brown to dark gray, generally concolorous but sometimes with an indistinct chevron pattern on the dorsal abdomen;
  • Microstigmatidae (Roewer 1942) — 7 genera, 16 species (Platnick WSCv13.5);
  • Barychelidae (Simon 1889) — 44 genera, 307 species (Platnick WSCv13.5);
  • Theraphosidae (Thorell 1869) — 124 genera, 946 species (Platnick WSCv13.5);
  • Paratropididae (Simon 1889) — 4 genera, 8 species (Platnick WSCv13.5);
• Family not presently determined;
• Genus not presently determined;
• Species not presently determined;

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References:

• Beccaloni, Jan. 2009. Arachnids. Univ. Calif. Press.
• Bond, Jason E. 1994. Seta-Spigot Homology and Silk Production in First Instar Antrodiaetus unicolor Spiderlings (Araneae: Antrodiaetidae). J. Arachnol., 22:19-22.
• Bond, J. E., and Platnick, N. I. (2007). A Taxonomic Review of the Trapdoor Spider Genus Myrmekiaphila (Araneae, Mygalomorphae, Cyrtaucheniidae). American Museum Novitates. Number 3596
• Coyle, Frederick A. 1983 . Aerial dispersal by mygalomorph spiderlings (Araneae, Mygalomorphae) . J. Arachnol., 11 :283-286.
• Coyle, Frederick A. and Wendell R. Icenogle. 1994. Natural History of the Californian Trapdoor Spider Genus Aliatypus (Araneae, Antrodiaetidae). J. Arachnol., 22:225-255.
• Coyle, Frederick A. 2005a. Antrodieaetidae. Ubick, et al., Spiders of North America, an Identification Manual, p. 39-40.
• Coyle, Frederick A. 2005b. Atypidae. Ubick, et al., Spiders of North America, an Identification Manual, p. 41-42.
• Comstock, John Henry. 1912. The spider book: a manual for the study of the spiders and their near relatives. University of Michigan.
• Emerton, James H. 1902. The Common Spiders of the United States. Kindle, hardcopy, and paperback editions.
• Foelix, Ranier F. 2011. Biology of Spiders, Third Ed. Oxford Univ. Press.
• Gertsch, Willis J., 1979. American spiders. Von Nostrand Reinhold Company.
• Hendrixson, Brent E., and Jason E. Bond. 2005a. Testing species boundaries in the Antrodiaetus unicolor complex (Araneae: Mygalomorphae: Antrodiaetidae): “Paraphyly” and cryptic diversity. Molecular Phylogenetics and Evolution 36: 405–416.
• Hendrixson, Brent E., and Jason E. Bond. 2005b.  Two sympatric species of Antrodiaetus from southwestern North Carolina (Araneae, Mygalomorphae, Antrodiaetidae). Zootaxa, 872: 1–19
• Herberstein, Marie Elisabeth (Ed.). 2011. Spider Behaviour: Flexibility and Versatility. Cambridge University Press.
• Howell, W. M., and R. L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Pearson Edu.
• Jackman, John A. 1999. A Field Guide to Spiders & Scorpions of Texas (Gulf Publishing Field Guide Series). Gulf Press.
• Kaston, B. J. 1978. How to know the spiders (The Pictured key nature series). WCB McGraw Hill.
• Levi, Herbert W., and Lorna Levi. 1987. Spiders and Their Kin (Golden Guide). Golden Press, New York.
• Paquin, Pierre, and Nadine Dupérré. 2003. Guide d’identification des Araignées (Araneae) du Québec. Association des entomologistes amateurs du Québec, p. 50.
• Platnick, Norman I. 2011a. The World Spider Catalog, V. 13.5; CURRENTLY VALID SPIDER GENERA AND SPECIES (Dec. 13, 2012). American Museum of Natural History.
• Preston-Mafham, Rod. 1996. The Book of Spiders and Scorpions. Barnes & Noble.
• Ubick, Darrell, and Pierre Paquin, Paula E. Cushing, V. Roth (Editors). 2005, Spiders of North America: An Identification Manual. American Arachnological Society.
• Vincent, Leonard S. 1993. The Natural History of the California Turret Spider Atypoides riversi (Araneae, Antrodiaetidae): Demographics, Growth Rates, Survivorship, and Longevity. J. Arachnol., 21:29-39.
• Wagner, James D., et al. 2003. Spatial Stratification in Litter Depth by Forest-Floor Spiders. J. Arachnol., 31:28-39.

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