Red-spotted Antmimic Spiders 29

This article by Jerry Cates, Dawn-Marie Hightower, Staci B., and Ashley A., first published on 3 August 2012, was last revised on 2 June 2024. © Bugsinthenews Vol. 13:08(02).

Over the past thirteen years or so, usually during the busiest time of the summer, I’ve received a smattering of photos from BugsInTheNews viewers depicting a black spider, most often with a bright red stripe down the middle of its dorsal abdomen, but sometimes with a small number of red dots at the abdomen’s dorsal posterior, aligned longitudinally. In each case the general morphology of the spider was such that it clearly was not a black widow (which has a shiny, bulbous, almost spherical abdomen), and thus was unlikely to be dangerous. I suspected, however, that — owing to the black widow’s bad reputation and these spiders’ superficial resemblance to it — most people might be moved to quickly destroy them, without so much as a second thought. If so, few if any would be able to provide me with a specimen to study.

In almost every case I was annoyed at myself once more for not recognizing the spider’s identity outright, and cursed the little time seemingly available to conduct a serious inquiry from scratch. That had always led me to inform the sender that not much could be learned from the photo. The darkness of the spider’s body, and the lighting in which the photo was taken, prevented the kind of character analysis that was necessary to key it to family, genus, and species.

“Please,” I would write back, “save the spider for me to examine under the microscope…”

But, alas, in every case but one, my plea was for naught. The sender nearly always replied that the spider was no longer in custody. It had either been destroyed (the most frequent situation) or released back into the wild.

College Station, TX; 03 Aug 2012: Original

Round Rock, TX; 26 July 2012: Original

And so the saga continued, year after year, with me still hoping that someone would eventually write back and say “No problem, Jerry, old chap. It’s in a glass jar just waiting for you to come and pick it up.” Well, this year — 2012 — is different. Though two photos of this species, shown above, followed the usual sequence, a third — received after I’d finally identified the species and posted the first two — arrived with the welcome words “I have the spider, still alive!“Photos of that spider are attached later in this article. First, though, we’ll discuss the two photos that preceded the third one, and my reaction to them.

The one on the right, found in Round Rock, Texas on 26 July by Staci B. (maddeningly, within a mile or so of my office), was released into the wild before Staci could get back to me. The one on the left, found by Ashley A. in College Station, Texas on 3 August, was pulverized into a misshapen mess by the Ashley’s mother, shortly after the photo was taken.

After receiving those first two photos, I decided to stop making excuses. Waiting for a specimen of this particular spider, which by any account appeared a lost cause, was just a delaying tactic on my part. The honest thing, I figured, would be to recognize it as such and deal with with it properly. Busy or no, I put aside what I was doing and found out — once and for all — what this spider’s name is. Besides posting the two raw photos above, I processed both with PhotoShop software, in what was expected to be a vain attempt to bring out added detail by enhancing contrasts, shadows, and brightness settings. The processed images, showing the maximum details that could be revealed, are posted below:

College Station, TX; 03 Aug 2012: Processed

Round Rock, TX; 26 July 2012: Processed

The resulting images, to my surprise, turned out to be far from useless. Though the eyes remained hidden in the darkness, a number of other details were revealed in them that were not evident in the originals:

1. The faces of both spiders are unusually flat, much like spiders in the Salticidae family of jumping spiders. That impression led me to conduct another thorough review of the Salticid literature, which — as before — produced nothing to suggest this species was a member of that family.
2. The palps, though not well defined in the spider from College Station, show no signs of being modified distally as are the palps of most male spiders. Such modifications are sometimes less noticeable in the Salticidae and in several other families, so this lack is less suggestive that this is a female as that both specimens are of the same gender. Markings often vary considerably between the sexes of the same species of spiders.
3. The carapace is elongated longitudinally, and is about as long and as wide as the abdomen, and these two body divisions are noticeably separated by a “waist”. That’s odd… For most spiders the carapace is either broader than the abdomen or dramatically smaller, and only rarely about the same length and breadth; furthermore, the two divisions are not usually sharply delineated by what might be thought of as a narrow waist.
4. Spiders whose body divisions are similar in size and shape, and whose major body divisions are separated by a narrow waist, are generally considered “antmimics,” for the fact that spider predators mistake the disguised spiders for certain ants and other, similar organisms found in their immediate environment. Some Salticid antmimics exhibit these features, but with noticeable constrictions, within the carapace, the abdomen, or both of those body divisions, that are ant-like or wasp-like, and — more to the point — quite un-spider-like.
5. The spider before us, however, retains its spider-like qualities in both the carapace and the abdomen, which is typical of antmimics from another grouping of spiders, those of the genus Castianeira in the Corinnidae family. The red-spotted antmimic (Castianeira descripta), in fact, has a black or mahogany brown body and a dorsal abdominal band of red along its midline. The scalloped edges of the red band pretty much nail our specimen. A close relative — also known as the red-spotted antmimic but with a different taxonomic name, Castianeira crocata, is identical to C. descripta in outward appearance, but has certain microscopic characters of its genitalia that differ enough to distinguish it as a separate species. The distributions of these two species overlap, and both are represented in some parts of Texas.

So, on 4 August 2012, I published the two photos, along with my identification of the spider. Six days later, on 10 August, an email was received from Dawn-Marie Hightower, of Taylor, Texas, with this subject line:

“I Have the Spider Still Alive!!“

She supplied a photo, which — though of such low resolution it will not be published here — was clearly the same species, and added the following note:

“Hello Jerry: I am in Taylor Tx and I still have the Black/Red spider still alive in a glass. As I have two small children I am not killing it until I know what it is and how much damage it’s bite can do. Below is a picture of the spider is question.“

Dawn not only sent an email, but also called me on the telephone. I informed her this spider is not known to pose a danger to her, her children, or her canine and feline pets. Since I was in town at the time we made arrangements to meet at the Lowes Home Improvement Store in Hutto that afternoon so she could hand the spider over for me to study under the microscope. Later that evening I did just that. The photos from that session are provided below:

200. Dorsal Habitus

201. Carapace

202. Eyes

203. Face

204. Dorsal pedicel

205. Abdominal band

206. Book lungs

207. Epigynum

208. Spinnerets

209. Sternum

210. Sternum

Anatomy:

• Body Size: (fig. 200) the specimen supplied by Dawn-Marie Hightower measured 7.9mm in body length; most Corinnidae measure from 1-15mm in body length (Ubick & Richman, 2005), placing this specimen near the median;
• Color: Except for book lungs and a band of red on the dorsal abdomen, the body is black to mahogany brown in color;
• Carapace: (fig. 201) pear-shaped/pyriform, truncated to form an elongated cephalic region extending anteriorly;
• Sternum: (figs. 209-10) oval, in the Corinnidae typically with precoxal triangles — also known as precoxal sclerites, consisting of triangular sclerotized extensions between the sternum and the coxae, sometimes fused with the sternum and sometimes free, with their pointed tips directed toward the coxae — but not obviously present in fig. 210 and possibly absent in this specimen;
• Eyes: (figs. 202-3) eight subequal eyes in two straight rows;
• Chelicerae: (fig. 209) with toothed margins, not visible in fig. 209, as the cheliceral claws (fangs) are retracted and obscure the margins of the cheliceral grooves in which the claws rest in the retracted state;
• Mouthparts: (fig. 209) endites longer than wide, constricted medially, with serrula; labium longer than wide;
• Legs: Though most Corinnidae have several pairs of ventral spines on the tibiae, those in the Castianiera have fewer pairs; the tarsi have 2 claws;
• Abdomen: (fig. 200) oval, absent obvious scutes;
• Spinnerets: (fig. 208) six, in a cluster; colulus present as small, narrow, fleshy lobe anterior of spinneret cluster;
• Respiratory system: (fig. 206) one pair of book lungs;
• Genitalia: female (figs 206-7) epigynum weakly sclerotized with two separate copulatory openings;

The Functionality of Ant Mimicry in Spiders

Most of the time, including the case before us with the red-spotted antmimic, when spiders mimic non-spider organisms in their surroundings, the mimicry is Batesian in form. In Batesian mimicry one organism (the mimic) that is harmless to its natural predators — and thus considered a prize morsel of food to them — adapts via natural selection a sufficient number of characters in its shape, form, coloration, and/or markings to outwardly imitate those of another organism (the model) that is harmful to the mimic’s natural predators. When those predators observe one or more of the mimicked characters, they mistake them as warning signs of the model. Instead of snatching the mimic up, they pass it by, preferring to eat one of its cousins that is not so fortuitously adorned.

This form of mimicry is named after the English naturalist Henry Walter Bates, whose work in the rainforests of Brazil led him to postulate that such mimicry evolves from the ordinary processes of natural selection. Predators seek out and exploit species that do not exhibit any of the warning signs of harmful organisms, leaving a disproportionately larger number of harmless species fortunate enough to serendipitously sport one or more such warning signs. Over time, species of prey that naturally exhibit a range of variation in body shape, coloration, and/or markings tend to produce more and more that mimic harmful organisms, and less and less of those that do not.

It should be noted that antmimics seldom fool the organisms they mimic. In many if not most cases — as for example in the one before us — they don’t even fool humans into thinking they are anything but spiders. Kaston (1978) points out that, in fact, the red-spotted antmimic doesn’t actually mimic an ant, but rather a red mutillid wasp. Even so, there seems little doubt that such wasps would mistake this spider for one of their numbers, or that we humans — on seeing such a spider — would think it a mutillid wasp, but that’s not the point. It is sufficient that some of the predators of these spiders (many of them other species of wasps) will be fooled, or momentarily confused, just long enough to allow the spider to escape. Some, unsure momentarily of its identity, might pass this particular spider by altogether, rather than chance an unfortunate encounter. In either case, the spider and its future offspring would benefit incrementally.

A special thanks to those who, since this article was first published, have found one or more of these spiders and offered to keep and send them to me. I no longer need additional specimens, however. Inasmuch as this spider is not known to be dangerous, it should be released back into the wild.

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Taxonomy:

• Kingdom Animalia (ahn-uh-MAYHL-yuh)  — first described in 1758 by the Swedish taxonomist Carolus Linnaeus [23 May 1707 – 10 January 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 [November 20, 1762 – February 6, 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 (Ser-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 [August 23, 1769 – May 13, 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 – 22 July 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 Araneomorphae (Uh-RAY-nee-oh-MOHR-fee) — distinguished from the mygalomorphae by having opposing fangs that open and close perpendicular to the spider body’s longitudinal axis, in a pinching action, whereas, in the mygalomorphae (e.g., tarantulas and trapdoor spiders), which have fangs that open and close more nearly in alignment with the spider body’s longitudinal axis.
• Series Entelegynae (inn-TELL-uh-jiy-nee) — araneomorph spiders which, unlike the Haplogynae, have hardened, i.e., sclerotized, female genitalia. Foelix (2011) points out that “entelegyne spiders have more complex reproductive organs (with an epigyne and separate fertilization ducts in the female)…” and that “Male entelegyne genitalia are very diverse…“;
• SuperfamilyCorinnoidea — a grouping of entelegyne spiders that includes the Corinnidae and Liocranidae families;
• FamilyCorinnidae —this family name, proposed by the Finnish arachnologist Pekka Lehtinen in 1967, and accepted by Jörg Wunderlich in 1986, was first described in 1880 by the German arachnologist Ferdinand Karsch (1853-1936), at the age of 27; it follows the naming of the genus Corinna, in 1841, by C. L. Koch, after the 6th century B.C. lyric poetess of that name; one wonders, too, if the Greek κορις (COHR-iss) = bug or fish, might not have figured in as well, inasmuch as many of these spiders are characterized as having morphological features similar to certain insects, particularly ants;
• Genus Castianeira — first described in 1880 by the German arachnologist Eugen von Keyserling (1833-1889), after Καστιανειρα (Castianeira), one of the wives of Priam in Homer’s Iliad; Kaston (1978) describes the genus as spiders that “run about over the ground and may resemble large ants or mutillid wasps“… they “resemble in form and manner of movement large carpenter ants, and they have been found associated with the ants. While ordinarily they move about slowly, like the ants, raising and lowering their abdomens and their front legs (which simulate the antennae of ants), they may run very rapidly when disturbed…“;
• Species Castianeira descripta or C. crocata(both of which were first described in 1847 by the French American arachnologist Nicholas Marcellus Hentz, 1797-1856)— Kaston (1978) describes C. descripta in these words: “The carapace and abdomen are deep mahogany brown to black. On the abdomen are red spots often restricted to the posterior end but sometimes extending forward to the anterior end. The legs have the femora dark like the carapace, but the distal segments are lighter, especially on legs I and II. Length of female 8 to 10 mm; of male 6.2 to 7.6 mm…“; Howell & Jenkins (2004) describe C. descripta thusly: “C. descripta has a longitudinal red band along the abdominal midline that gives it the appearance of a red mutillid wasp. The red band in some individuals is reduced to a series of red dots extending the length of the abdomen or limited to small red dots at the posterior end of the abdomen. The remainder of the abdomen and cephalothorax is brown or black. The femora of the legs are brown or black, similar to the color of the body. The distal segments of legs I and II are yellow. Tibia I and II have two pairs of ventral spines…“

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References to Relevant Scientific Literature:

• Ahrens, Lily, and Johanna M. Kraus. 2006. Wolf Spider Movement Along a Pond Edge. J. Arachnology 34:532-539.
• Beccaloni, Jan. 2009. Arachnids. Univ. Calif. Press.
• Brady, Allen R. and Kelly S. McKinley. 1994. Nearctic Species of the Wolf Spider Genus Rabidosa (Araneae: Lycosidae). J. Arachnology 22:138-160.
• Brady, Allen R. 2007. Sosippus Revisited: Review of a Web-building Wolf Spider Genus from the Americas (Araneae, Lycosidae). J. Arachnology 35:54-83.
• Comstock, John Henry. 1912. The spider book: a manual for the study of the spiders and their near relatives. University of Michigan.
• Dean, D. Allen. 2012. Catalog of Texas Spiders. Texas A&M University.
• Dondale, Charles D., and James H. Redner. 1978. Revision of the Nearctic wolf spider genus Schizocosa (Araneida: Lycosidae). The Canadian Entomologist110(2):143-181.
• Dondale, Charles D., and James H. Redner. 1983. Revision of the genus Arctosa C. L. Koch in North and Central America (Araneae:Lycosidae). J. Arachnology 11:1-30.
• Dondale, Charles D. 2005. Chap. 37: Lycosidae, in Ubick et al., 2005, Spiders of North America: An Identification Manual. American Arachnological Society.
• 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.
• 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.
• Lubin, Yael, and Trine Bilde. 2007. The Evolution of Sociality in Spiders. Adv. Study of Behav. 37.
• Platnick, Norman I. 2012a. The World Spider Catalog, Version 12.5; FAM. CORINNIDAE Karsch, 1880c: 374 [urn:lsid:amnh.org:spiderfam:0049]. American Museum of Natural History.
• Platnick, Norman I. 2012b. The World Spider Catalog, Version 12.5; Currently Valid Spider Genera and Species. American Museum of Natural History.
• Preston-Mafham, Rod. 1996. The Book of Spiders and Scorpions. Barnes & Noble.
• Uetz, George W., Jennifer Bischoff, and Joseph Raver. 1992. Survivorship of Wolf Spiders (Lycosidae) Reared on Different Diets. J. Arachnology 20:207-211.
• Vogel, Beatrice R. 2004. A Review of the Spider Genera PARDOSA and ACANTHOLYCOSA (Araneae, Lycosidae) of the 48 Contiguous United States. J. Arachnology 32:55-108.
• Wickler, Wolfgang.1968. Mimicry in Plants and Animals. World University Library.

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