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The Sonoran Desert toad (Incilius alvarius) is the largest native toad in the United States ([less than or equal to] 200 mm total length) and occurs near perennial and seasonal bodies of water across southern Arizona, southwestern New Mexico, and northwestern Mexico (Brennan and Holycross, 2006; Rorabaugh and Lemos-Espinal, 2016). It is a dietary generalist and known prey items include invertebrates (e.g., beetles, ants, moths, and small spiders), small lizards, small toads, and mice (King, 1932; Cole, 1962; Jennings and Hayes, 1994; Brennan and Holycross, 2006). Analyses of stomach contents of numerous Sonoran Desert toads have identified terrestrial beetles as being the predominant prey item (ortenburger and ortenburger, 1926; Bogert and Oliver, 1945). Other researchers have noted the presence of harvester ants (Pogonomyrmex), velvet ants (Timulla), and scorpions (Scorpiones) in stomachs of Sonoran Desert toads (Gates, 1957; Cole, 1962), suggesting these toads are capable of eating prey that have formidable biting and stinging defenses.

On 28 August 2016 at 1945 h, we observed a large (~175 mm total length) Sonoran Desert toad attempting to eat a large (~45 mm body length, ~90 mm leg span) western desert tarantula (Aphonopelma chalcodes) at Sabino Canyon, Arizona. Upon finding the toad (using a headlamp), we noticed tarantula legs sticking out of the toad's mouth, with approximately 90% of the spider contained in the mouth and throat of the toad (Fig. 1a). The toad likely attacked the tarantula from behind, attempting to swallow its abdomen first and its legs last, but we do not know how long the interaction had transpired before we arrived. We watched for approximately 45 s as the toad attempted to finish swallowing the tarantula. During this time, however, the tarantula appeared to fight back, and the toad struggled to contain it. The toad repeatedly blinked and drew its nictitating membranes across its eyes (Fig. 1b). We also observed protrusions through the skin of the toad's throat which may have been the tarantula's chelicerae and fangs striking from inside the toad. it is likely that the tarantula also was ejecting urticating hairs from its abdomen into the throat of the toad (Battisti et al., 2011). After 45 s of observation, the toad suddenly wretched, and the tarantula sprang out of its mouth (Fig. 1c). The tarantula quickly scurried away, covered in slime and with two legs seeming to be impaired (i.e., not fully articulating), but wholly intact (Fig. 1d). The toad sat still for approximately 30 s before hopping away downhill.

Sonoran Desert toads have been described as eating anything that fits in their mouths (Fouquette et al., 2005), even prey items "endowed with seemingly formidable protective devices" (Cole, 1962). Although tarantulas are larger than previously documented prey, and much larger than other prey with biting and stinging defenses (e.g., scorpions, wasps (Vespidae), and ants), they nonetheless can fit in the mouth of a Sonoran Desert toad. Another toad species (Anaxyrus americanus) preys upon bombardier beetles (Carabidae) despite the potent chemical defenses of those beetles. However, Dean (1980) found that toads frequently reject bombardier beetles after attempting to ingest them and "exhibit behavior that suggests discomfort and display temporary aversion to striking again at the beetle." Tarantulas are very common in Sonoran Desert and, similar to toads, are most active during summer evenings (Lizotte, 2000). This behavioral similarity likely increases the probability of toad-tarantula interactions. Our observation suggests that toads certainly try to consume tarantulas. How frequently Sonoran Desert toads successfully prey on tarantulas, or what their aversion to tarantulas may be following failed predation attempts, remain unknown.

We thank D.D. Houser for translating the abstract and two anonymous reviewers for their helpful comments on an earlier version of this manuscript.

Literature Cited

Battisti, A., G. Holm, B. Fagrell, and S. Larsson. 2011. Urticating hairs in arthropods: their nature and medical significance. Annual Review of Entomology 56:203-220.

Bogert, C. M., and J. A. Oliver. 1945. A preliminary analysis of the herpetofauna of Sonora. Bulletin of the American Museum of Natural History 83:297-426.

Brennan, T. C., and A. T. Holycross. 2006. A field guide to amphibians and reptiles in Arizona. Arizona Game and Fish Department, Phoenix, Arizona.

Cole, C. J. 1962. Notes on the distribution and food habits of Bufo alvarius at the eastern edge of its range. Herpetologica 18:172-175.

Dean, J. 1980. Encounters between bombardier beetles and two species of toads (Bufo americanus, B. marinus): speed of prey-capture does not determine success. Journal of Comparative Physiology 135:41-50.

Fouquette, M. J., Jr., C. W. Painter, and P. Nanjappa. 2005. Bufo alvarius Girard, 1859 Colorado River toad. Pages 384-386 in Amphibian declines: the conservation status of United States species (M. J. Lannoo, editor). University of California Press, Berkeley.

Gates, G. O. 1957. A study of the herpetofauna in the vicinity of Wickenburg, Maricopa County, Arizona. Transactions of the Kansas Academy of Science 60:403-418.

Jennings, M. R., and M. P. Hayes. 1994. Amphibian and reptile species of special concern in California. California Department of Fish and Game, Rancho Cordova.

King, F. W. 1932. Herpetological records and notes from the vicinity of Tucson, Arizona, July and August, 1930. Copeia 1932:175-177.

Lizotte, R. 2000. Spiders. Pages 294-303 in A natural history of the Sonoran Desert (S. J. Philips and P. W. Comus, editors). university of California press, Berkeley.

Ortenburger, A. I., and R. D. Ortenburger. 1926. Field observations on some amphibians and reptiles of Pima County, Arizona. Proceedings of the Oklahoma Academy of Science 6:101-121.

Rorabaugh, J. C, and J. A. Lemos-Espinal. 2016. A field guide to the amphibians and reptiles of Sonora, Mexico. Eco Herpetological Publishing, Rodeo, New Mexico.

Submitted 7 September 2016. Accepted 19 February 2017.

Associate Editor was Felipe de Jesus Rodriquez-Romero

Michael T. Bogan * and Drew E. Eppehimer

School of Natural Resources and the Environment, University of Arizona, 1064 East Lowell Street, Room N384, Tucson, AZ 85721

* Correspondent:

Caption: Fig. 1-Attempted predation of a western desert tarantula (Aphonopelma chalcodes) by a Sonoran Desert toad (Incilius alvarius) at Sabino Canyon, Arizona, on 28 August 2016: (a) our initial observation, (b) the toad reacting to the tarantula's defenses, (c) the toad wretching, and (d) the tarantula's escape.
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Title Annotation:NOTES
Author:Bogan, Michael T.; Eppehimer, Drew E.
Publication:Southwestern Naturalist
Geographic Code:1U8AZ
Date:Jun 1, 2017

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