— BugsInTheNews is a VIEWER-PARTICIPANT WEBSITE. This article, by Jerry Cates and Regina Weishuhn, was first published on 29 April, 2012. It was last revised on 8 July 2012. © Bugsinthenews Vol. 13:04(04). Note: Regina has recently provided additional images which are in process and will be posted as soon as possible.
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Regina Weishuhn, of Grand Prairie, Texas, wrote the following on 18 April 2012:
She attached two images to that email, both of extraordinarily beautiful crab spiders that she had found in her extensive flower garden. I wrote back that they were both crab spiders in the Thomisidae family, and that I would be adding them to the website, as additions to the two existing pages on crab spiders, one that was photographed near Athens, Texas and another that was collected at a medical facility in Cameron, Texas. I then asked if by chance she had taken more photos. It happened she had. Soon a wealth of images came my way, for which I — and, no doubt, soon a host of viewers — am and are grateful.
If you, like me, are interested in the kind of camera Regina used to photograph these spiders, the embedded file information revealed it to be a Canon EOS Rebel T3. Of course, having a great camera is a good start, but knowing how to use it expertly, as Regina did, is another. Thanks, Regina, for the care and attention you paid to the composition of these images. I have cropped and processed them lightly, to bring out important details, but they are otherwise unmodified.
NOTE: all photos on this web page may be enlarged for more detailed viewing by positioning your cursor over the photo and clicking.
Crab spiders in the Thomisidae family will bite if handled. In fact, they are among our more pugnacious arachnids, and often bite without provocation. Their venom, however, is not considered dangerous to humans, though the bite wound may turn red and produce a swelling of several day’s duration.
These two spiders — one a male, the other a female — appear to be members of the genus Mecaphesa. I have tentatively identified the male as Mecaphesa celer (Hentz, 1847), and the female as Mecaphesa asperata (Hentz, 1847). On one level, the fact they represent two separate species is surprising. One authority (Preston-Mafham, 1996, p. 25) points out that the much smaller males of the species Misumena vatia enjoy an amicable relationship with their much larger females, to the point that the former often hitch rides on the backs of the latter and share in whatever the female catches; all this is done without fear of being eaten, with the added benefit of being permitted to mate with the female at will, again without risking death in the process. It is not known if the same kind of gratuitous relationship typifies the dimorphic sex partners of the genus Mecaphesa. However, Regina did not find the partners of either of these two species despite conducting a thorough search after I asked for additional photos. I did not specifically ask her to find their partners, but it seems doubtful that, had she found them, she would have passed over the temptation to take their photographs.
The remarkable coloration of the female is presumed to be a beneficial adaptation referred to as mimicry. In this case the mimicry is optical in nature, but mimicry can take many other forms (olfactory, geometrical, auditory, etc.) as well. For another example of optical mimicry, see the article on eastern hog-nosed snakes mimicking the pygmy rattlesnake in the Sam Houston National Forest. Optical mimicry, for its part, occurs in a number of forms as well; the form observed in the SHNF eastern hog-nosed snakes appears to be Batesian (wherein a non-venomous or palatable organism mimics a venomous or non-palatable one), while the form observed in the female spider shown here seems merely to be a kind of camouflage. The spider takes on the dominant colors of the flowers on which it sits while awaiting the arrival of prey.
Whether the coloration is temporary or permanent varies from species to species, but a number of authorities (Foelix, 2011, pp. 311-312; Wickler, 1968, p. 54) describe it as permanent in Micrommata viriscens and Araniella cucurbitina (Foelix), and reversible in Misumena vatia (Wickler), Misumena varia, and Thomisus onustus (Foelix, p. 311). According to Wickler, the reversible change from white to yellow in Misumena vatia occurs as a result of the transfer of a liquid pigmented material from the intestine to the skin; the pigment is withdrawn to return to a white coloration. Foelix, writing 43 years later, explains that the color change in Misumena varia and Thomisus onustus, which takes place over several days, is due either to the production or destruction of ommochromes, or yellow pigments; in the white coloration, the spider’s skin contains mostly — what are evidently somewhat large — intracellular guanine crystals and a small quantity of relatively tiny yellow ommochromes (pro-granules, or precursors to larger yellow crystals); when the spider is moved to change from white to yellow, the pro-granules slowly aggregate, gradually changing the spider’s skin from white to yellow.
The benefits conferred by optical mimicry in these spiders have been the subject of much conjecture in the past, and remain controversial even today, almost 150 years after Henry Bates first postulated his theory of optical mimicry in Amazonian butterflies. Foelix, for example, points out that although it seems logical that camouflaged spiders should both acquire more prey by stealth, and be passed over more often by predators by virtue of being colored like the flowers they inhabit, the results of several recent studies suggest we only vaguely understand the full extent of the benefits such “camouflage” provides. I won’t attempt to summarize those studies here, but suffice it to say that we have only scratched the surface, and much, much more remains to be learned about such things…
Regina’s spiders are close relatives of the crab spiders previously posted from Athens and Cameron, Texas, so the material posted on those pages provides added information about the family it hails from.
We are technically constrained from arriving at an absolutely accurate identification of these specimens for the same reasons mentioned in those other pages: as Prof. Pekka Lehtinen, Turku University, Finland, pointed out (pers. comm. 2 Dec 2011) regarding a previous spider under investigation, whenever the ventrum is not in view (as with Regina’s female), the general aspects of the epigynum cannot be determined. This is generally the case for any spider examined as a live specimen in its native habitat. Similarly, the specifics of the pedipalps (for the male), though sometimes visible in photos of live specimens of some spider families, are less so with the Thomisidae, and in any case are not depicted in Regina’s photos with the detail necessary to speak to the palpal characters hinging on speciation. As with most entelegyne spiders, the morphology of the external male and female genitalia is crucial in distinguishing one species from another.
The identity of these spiders as members 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).
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 174 genera and 2151 species (as of 31 December 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 by either of the specimens posted here.
- Misumenoides — 1 species, M. formosipes (Walckenaer 1837) is found in North America, and that species is distributed widely; the anterior eyes (the four eyes that form a row across the anterior face, as depicted for the female in 104, and for the male in 201) are of equal size in the Misumenoides and appear equal in size in both of Regina’s spiders — but, while the eyes of M. formosipes are immersed in a distinctive white eye mask, that character is not evident in Regina’s female specimen and — if present in the male — is obscured by that spider’s overall pale coloration, unlike in typical specimens of M. formosipes.
- 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 — from all the evidence in the photos posted here — also in both of Regina’s spiders.
- 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 Regina’s spiders.
- 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; 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; S. viridans has a green carapace and legs, and an abdomen maculation, while Regina’s spiders have no trace of green (ref: BugGuide, Thomisidae: Synema).
- 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 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); species in the genus Diaea also exhibit prolateral macrosetae on metatarsus I.
- Misumenops — 25 species have been identified in North America, and are widespread; these spiders have lateral eyes situated on completely conjoined tubercles; 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).
- Mecaphesa — 18 North American species, all moved here from the genus Misumenops following the latter’s redescription by Lehtinen in 2008. These spiders have lateral eyes situated on completely conjoined tubercles and lack prolateral macrosetae on metatarsus I, as in the Misumenops. Note the fully conjoined tubercles of the lateral eyes for Regina’s female spider in figs. 102-104, and for the male spider in fig. 207. Metatarsus I of the female, depicted in figs. 108-110, and for the male in figs. 201, 205, and 206, are shown without evidence of prolateral macrosetae:
- M. aikoae (Schick, 1965)
- M. asperata (Hentz, 1847)
- M. californica (Banks, 1896)
- M. carletonica (Dondale & Radner, 1976)
- M. celer (Hentz, 1847)
- M. coloradensis (Gertsch, 1933)
- M. deserti (Schick, 1965)
- M. devia (Gertsch, 1939)
- M. dubia (Keyserling, 1880)
- M. gabrielensis (Schick, 1965)
- M. importuna (Keyserling, 1881)
- M. importuna belkini (Schick 1965)
- M. lepida (Thorell, 1877)
- M. lowriei (Schick, 1970)
- M. quercina (Schick 1965)
- M. rothi (Schick, 1965)
- M. schlingeri (Schick, 1965)
- M. sierrensis (Schick, 1965)
- M. verityi (Schick, 1965)
- Xysticus — 67 species have been found in North America, and are widespread; these species have lateral eyes situated on incompletely conjoined tubercles; tibia I presents with more than 2 pairs of ventral macrosetae; femur I in the Xysticus is rather slender, some 4 times longer than wide.
- Ozyptila — 20 species have been identified in North America, and are widespread; these species have lateral eyes situated on incompletely conjoined tubercles; tibia I has no more than 2 pairs of ventral macrosetae; femur I is about 3 times longer than wide.
Cited References & Resources for Additional Research:
- Anderson, John F., 1996. Metabolic rates of resting salticid and thomisid spiders. J. Arachnology 24:129-134.
- Beccaloni, Jan. 2009. Arachnids. University of California Press, p. 34.
- Carrel, James E., and R.D. Heathcote, 1976. Heart Rate in Spiders: Influence of Body Size and Foraging Energetics. Science, 193: 148-150.
- Comstock, John H., 1912. The spider. Doubleday, Page & Company.
- Dondale, Charles D. 2005. Thomisidae; Chap. 24, Ubick, et al., 2005, pp. 246-247. Published by the American Arachnological Society.
- Emerton, James H., 1902. The common spiders of the United States. Dover Books.
- Foelix, Rainer F. 2011. Biology of Spiders, Third Edition. Oxford University Press.
- Gertsch, Willis J., 1979. American Spiders, 2nd Edition. Von Nostrand Reinhold Company.
- Hillyard, Paul, 1994. The book of the spider. Random House Inc.
- Howell, W. Mike, and Ronald L. Jenkins. 2004. Spiders of the Eastern United States; a photographic guide. Pearson Education; pp. 285-298.
- Jackman, John A., 1997. A field guide to spiders & scorpions of Texas. Gulf Publishing Co., pp. 14, 19, 21-22, 120, 122-126, P22.
- Jiménez, Maria-Luisa, 1992. New species of crab spiders from Baja California Sur (Araneae: Thomisidae). J. Arachnology 20:52-57.
- Keyserling, Herman Graf. 1880. Die Spinnen Americas — Laterigradae. Verlag von Bauer & Raspe.
- Kaston, B. 1978. How to Know the Spiders. McGraw-Hill.
- Lehtinen, P. T. 2000. Generic revision of some thomisids related to Xysticus C.L.Koch, 1835 and Ozyptila Simon, 1864. European Arachnology 2000, pp. 315-327.
- Lehtinen, P. T. & Y. M. Marusik. 2008. A redefinition of Misumenops F. O. Pickard-Cambridge, 1900 (Araneae, Thomisidae) and review of the New World species. Bulletin of the British Arachnological Society. 14: 173-198.
- Levi, H. and L. Levi. 1987. Spiders and their Kin. Golden Press, New York.
- Platnick, Norman I. 2011a. The World Spider Catalog, V. 12.0; FAM. THOMISIDAE Sundevall, 1833b: 27 [urn:lsid:amnh.org:spiderfam:0058]. American Museum of Natural History.
- Preston-Mafham, R. 1996. The Book of Spiders and Scorpions. Barnes & Noble.
- Salmon, J., and N. Horner. 1977. Aerial dispersion of spiders in North Central Texas. J. Arachnology, 5:153-157.
- Schmalhofer, Victoria R., 1999. Thermal tolerances and preferences of the crab spiders Misumenops asperatus and Misumenoides formosipes (Araneae, Thomisidae). J. Arachnology, 27:470-480.
- Schmalhofer, Victoria R., 2000. Diet-induced and morphological color changes in juvenile crab spiders (Araneae, Thomisidae). J. Arachnology 28:56-60.
- Ubick, D., P. Paquin, P.E. Cusing and V. Roth, editors, 2005. Spiders of North America. Published by the American Arachnological Society.
- Young, O . P. and G . B. Edwards . 1990. Spiders in United States field crops and their potential effect on crop pests. J. Arachnology, 18:1-27.
- Wickler, W. 1968. Mimicry in Plants and Animals. World University Library.