A Thomisid Crab Spider near Athens, Texas

BugsInTheNews is a VIEWER-PARTICIPANT WEBSITE. This article by Jerry Cates and Amanda L., first published on 29 November 2011, was last revised on 13 July 2012. © Bugsinthenews Vol. 12:11(3).

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Araneae: Thomisidae: Amanda L., Athens, TX --- 29 Nov 2011

001. Habitus

Araneae: Thomisidae: Amanda L., Athens, TX --- 29 Nov 2011

002. Habitus

Amanda wrote:

“I found this spider in my son’s toy box on 11/29/11.

We live in East Texas (close to Athens).

Is there any way you can tell me if it is a poisonous spider?

Thanks, Amanda L.”

I wrote Amanda back to let her know that this is a crab spider in the Thomisidae family.

Thomisids are not considered dangerous although they — along with practically all other spiders — will bite if handled, particularly if handled roughly. If you play with spiders, you will probably get bitten, but most spider bites do not produce medical symptoms beyond the local area of the bite itself. Note: if you have been bitten by a spider, read the material on the link at the head of this article on SPIDER BITE FIRST AID. For information on exterminating and controlling spiders in your environment read the material at the link under that title.

Collectors report that bites from crab spiders are relatively common if the spiders are brought into contact with the collector’s skin. Crab spider bites on fingertips sometimes cause the bitten finger to swell to twice its normal size and become somewhat discolored; generally the swelling and discoloration lasts a few hours before the digit returns to normal size and coloration.

The venom of most crab spiders produces, in most people, a small welt that will be reddened for a day or so, and may — for sensitive individuals — be more extensive, as described above. It is always wise, however, to consult with a medical practitioner whenever complications from a spider bite are observed, particularly if the person bitten experiences symptoms beyond the immediate bite, such as difficulty breathing, disorientation, changes in heart rate or blood pressure, and the like, or if unusual swelling or discoloration at the bite wound lasts more than a few hours.

Taxonomy:

Amanda’s specimen, though not the same species as the crab spider I found in Cameron, Texas back in July, is a close relative of that spider, so the material posted on that page provides added information about the family it hails from. We are constrained from arriving at an accurate identification of this specimen for several reasons: first, as Prof. Pekka Lehtinen, Turku University, pointed out (pers. comm. 2 Dec 2011), the ventrum is not in view and the general aspects of the epigynum (this is a female, judging from the pedipalps), cannot be examined. As with most entelegyne spiders, the morphology of the external female genitalia is crucial in distinguishing one species from another.

Araneae: Thomisidae: Dorsal carapace & palps; Amanda L., Athens, TX --- 29 Nov 2011

003. Carapace & palps

Araneae: Thomisidae: Dorsal abdomen; Amanda L., Athens, TX --- 29 Nov 2011

004. Dorsal abdomen

At least the identity of this spider as a member of the Thomisidae family appears rather straight-forward:

Though a number of other spider families exhibit anatomical and behavioral traits that are crab-like, only spiders in the Thomisidae have legs such that the first two, on each side (counting from the head backward) are long and stout, while the third and fourth legs on each side are comparatively short and slender (see Keyserling, 1880, p. 2, and Dondale, 2005, in Ubick et al., p. 246).

Notice in images 001 and 002 that Amanda’s spider has two very stout, relatively long legs (Legs I and II) in front of two much shorter, more slender legs (Legs III and IV).

Members of the Thomisidae are distributed worldwide. According to the American Museum of Natural History’s World Spider Book, edited by Dr. Norman I. Platnick, these spiders are presently represented by 177 genera and 2152 species (as of 30 November 2011); and, according to Dondale, writing in Ubick, et al., 2005, pp. 246-247, the subset of these thomisids that are found in North America were in 2005 represented by nine genera, within which some 130 species are presently recognized.

I list these nine genera, along with a few notes pertaining to the species presumed to belong to them, below, as the present state of thomisid taxonomy — at least in North America — is only slowly coming to grips with the taxonomical revisions of Lehtenin & Marusik, 2008, which introduce drastic changes to the present nomenclature (some of which are briefly discussed below):

  • Tmarus — 6 species have been found in North America, and are widespread; the species in this genus have a protruding carapace and a distinctive posterior abdominal tubercle, neither of which seems to be exhibited in Amanda’s specimen (see images  003 and 004).
  • Misumenoides — 1 species, M. formosipes (Walckenaer 1837) is found in North America, and that species is distributed widely, but its anterior eyes (the four eyes that form a row across the anterior face and annotated as ALE and AME in image 005) are of equal size in the Misumenoides, while the anterior eye row of Amanda’s specimen appears to comprise eyes of unequal diameters, as seemingly demonstrated in image 005: e.g., the leftmost anterior lateral eye (ALE) seems to be noticeably larger than the leftmost anterior median eye (AME), though the image quality may be conveying a false impression in this regard, as the disparity between the rightmost ALE and AME is not so obvious [ed. note: conjecture regarding relative eye size, based on evidence taken from these photos alone, is unreliable] — and, while the eyes of M. formosipes are immersed in a distinctive white eye mask, that character is not evident in Amanda’s specimen, though the portion of the face between the specimen’s ALEs is a lighter coloration than its surroundings.
  • Misumena — 2 species have been found in North America: M. vatia (Clerck 1757), commonly known as the Goldenrod Crab Spider, and M. fidelis (Banks 1898). Though absent the white eye mask of Misumenoides, spiders in the genus Misumena have anterior eyes of equal size, as in the Misumenoides and, as previously noted, possibly contrary to the anterior eyes of Amanda’s specimen.
  • Coriarachne — 4 species have been found in North America, and are distributed widely. These spiders have exceptionally flat carapaces, such that the carapace is as low at the level of coxa III as at the posterior eye row (Dondale, in Ubick et al., 2005, p. 246); this distinctive morphological feature cannot be ruled out for Amanda’s specimen, though it is not possible to accurately gauge the flatness of the carapace from the photos Amanda supplied.
  • Synema — 3 species, distributed throughout the southern U.S., except along the west coast: S. neomexicana has a carapace that is uniformly dark brown with a narrow white seam, and a dorsal abdomen that is grey to white, not the reddish coloration of the carapace (images 001, 002, 003) and the brownish coloration of the dorsal abdomen (images 001, 002, 004) of Amanda’s specimen; S. parvulum has an abdomen with a large dark caudal maculation, i.e., the posterior of the abdomen is darkened, but the remainder is otherwise pale in color; furthermore, the eyes of the anterior eye row are nearly straight, and the carapace is a light brown, all of which seems quite unlike the presentment of Amanda’s specimen (images 001, 002, 003, 004, 005), though judging the straightness of the eyes of Amanda’s specimen from these photos is unreliable; S. viridans has a green carapace and legs, and an abdomen maculation, while Amanda’s specimen has no trace of green, and its entire dorsal abdomen (image 004) is uniformly dark (ref: BugGuide, Thomisidae: Synema).
Araneae: Thomisidae: Eyes; Amanda L., Athens, TX --- 29 Nov 2011

005. Eyes

Araneae: Thomisidae: Leg I Femur; Amanda L., Athens, TX --- 29 Nov 2011

006. Leg I Femur

Araneae: Thomisidae: Leg I Tibia & Metatarsus; Amanda L., Athens, TX --- 29 Nov 2011

007. Leg I Tibia

008. Distal Left Leg I

008. Distal Left Leg I

009. Distal Right Leg I

009. Distal Right Leg I

  • Diaea — 2 species, ditributed throughout California and Florida. D. seminola (whose description presently eludes me) is found in Florida, and D. livens, an import from Europe with a distinctive greenish coloration similar to that of S. viridans, is found in California and possibly is more widespread than that; both species, however, have lateral eyes that are situated on completely conjoined tubercles, (knob-like outgrowths that are so conjoined as to form a single outgrowth within which both eyes are situated), while Amanda’s specimen presents with lateral eyes situated on what appear to be, if anything, incompletely conjoined tubercles (image 005, where the tubercles of the PLE are rather obvious, but the ALE appear to be on separate tubercles somewhat reduced from those of the PLE); species in the genus Diaea also exhibit prolateral macrosetae on metatarsus I, which, while not evident with certainty in Amanda’s specimen, would be difficult to diagnose from the photos she supplied; as 008 and 009 show, two possible prolateral macrosetae appear on the right and left metatarsus of leg I (Ta = tarsus, Mt = metatarsus, and Ti = tibia), and hints of others appear evident (though it is risky to speculate on this, given these images alone).
  • Misumenops — 25 species have been identified in North America, and are widespread; these spiders have lateral eyes situated on completely conjoined tubercles, which — as in the case of Diaea — appear to be ruled out for Amanda’s specimen; these species lack prolateral macrosetae on metatarsus I. — NOTE: Virtually all of the nearctic species previously placed in this genus have been moved to the genus Mecaphesa. Lehtinen redescribed the type species of that genus and transferred a large number of species into Mecaphesa in 2008. Presently, this latter genus is shown, in Platnick’s World Spider Catalog, to contain at least 18 North American species (BugGuide: Mecaphesa).
  • Xysticus — 67 species have been found in North America, and are widespread; these species have lateral eyes situated on incompletely conjoined tubercles, which cannot be ruled out for Amanda’s specimen; tibia I presents with more than 2 pairs of ventral macrosetae (a feature clearly present in Amanda’s specimen, as shown in image 007); femur I in the Xysticus is rather slender, some 4 times longer than wide, while that of Amanda’s specimen (image 006) appears to be somewhere between 3 and 4 times longer than wide, which — initially — I concluded as arguing against an assignment within this genus, but Dr. Schmalhofer, in a personal communication received on 5 Dec 2011, suggests that the measurement of femur I on Amanda’s specimen is consistent with Xysticus, and that the possibility exists that Amanda’s spider is Xysticus funestus Keyserling 1880.
  • Ozyptila — 20 species have been identified in North America, and are widespread; these species have lateral eyes situated on incompletely conjoined tubercles, a possibility for Amanda’s specimen, but tibia I has no more than 2 pairs of ventral macrosetae, while we see what appear to be 7 pairs in Amanda’s specimen (as shown in 007, the 7 visible macrosetae of tibia I are all ventral); femur I is about 3 times longer than wide (image 006), which may be inconsistent with Amanda’s specimen.

Using the key to the genera of the Thomisidae found in Ubick, et. al., 2005, p. 267, as a means of homing in on the genus this specimen falls into enables us to eliminate several genera from contention: namely  Tmarus, Misumenoides, Misumena, Synema, Diaea, and Misumenops/Mecaphesa.

Coriarachne cannot be ruled out, so a further analysis of the four species in that genus that are found in North America is underway. Similarly, we cannot rule out Xysticus or Oxyptila, though the latter seems a less likely possibility than the former. Besides conducting a more thorough review of the extant literature on the Coriarachne, Misumenops/Mecaphesa, Xysticus, and Ozyptila, I have also begged the opinions of three thomisid specialists: Prof. Pekka T. Lehtinen (Prof. Emeritus, Zoological Museum, Turku University, Finland), Victoria Schmalhofer (Rutgers University), and Prof. Ingi Agnarsson (University of Puerto Rico). Pekka Lehtinen and Victoria Schmalhofer have replied to my inquiry, supplying intriguing answers. As I told these scientists, their pithy replies remind me how much more I need to learn, but that doesn’t discourage, but rather spurs me on to learn more.

Cited References & Resources for Additional Research:

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