Chihuahuan Hook-nosed Snake – Tucson Herpetological Society

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Chihuahuan Hook-nosed Snake (Gyalopion canum)

[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2099″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Chihuahuan Hook-nosed Snake, San Pedro River Valley, AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2290″ img_size=”medium” add_caption=”yes” alignment=”center” onclick=”img_link_large”][vc_column_text]Chihuahuan Hook-nosed Snake, Cochise County © 1991 Manny Rubio / ASDM Sonoran Desert Digital Library[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Chihuahuan Hook-nosed Snake (Gyalopion canum) is a small species (384 mm total length [TL]) with a narrow tip to the snout that is upturned. The rostral is flat or concave at its broadest point and contacts the postocular scales. Loreal scales are usually absent (rarely one per side). The dorsal scales are smooth and in 17 rows at mid-body. The anal plate and subcaudals are divided. The dorsal pattern consists of 25-52 dark bordered dark brown bands or saddles on the body, and 8-15 on the tail. The background coloration is a lighter gray or gray brown to yellowish brown sometimes with vague, darker mottling interspersed. The dark bands narrow and often break up laterally. A dark bar crosses through the eyes and across the posterior portion of the snout. The venter is cream or white often with a central pink area. Gender is not reliably distinguished by external morphology. Females have a small hemipenis that is less developed than that of the male (Degenhardt et al. 1996, Ernst and Ernst 2003, Brennan and Holycross 2006).

No subspecies of the Chihuahuan Hook-nosed Snake are recognized (Crother 2012). Holm (2008) found G. canum to be more closely related to the hook-nosed snakes in the genus Ficimia than to G. quadrangulare of southern Arizona. Similarly, Pyron et al. (2013) found a close relationship between G. canum and F. streckeri (Taumalipian Hook-nosed Snake).

In Arizona, the Chihuahuan Hook-nosed Snake is most likely to be confused with the Mexican Hog-nosed Snake (Heterodon kennerlyi) or the Spotted Leaf-nosed Snake (Phyllorynchus decurtatus). The former grows much larger (< 760 mm TL in Arizona), the dorsal scales are keeled, the rostral is strongly keeled, and the venter is yellow with black blotches. The Spotted Leaf-nosed Snake occurs mostly to the west of the range of the Chihuahuan Hook-nosed Snake, the rostral is greatly enlarged and folded up over the snout, and the anal plate is undivided.

This is a rarely encountered snake in our area. Only 36 Arizona specimens are listed on HerpNet; most of those are within the 100-Mile Circle. The westernmost records are in the Pajarito/Atascosa Mountain range complex, from Sycamore Canyon east to Nogales. There are also records for the Sonoita area and the nearby site of historic Fort Buchanan, Highway 83 in the Empire Mountains, the Santa Rita Mountains, the upper San Pedro River Valley, Huachuca Mountains, Sulphur Springs Valley a few miles west of Chiricahua National Monument, Highway 80 northeast of Douglas, near Safford, and seven miles northeast of Guthrie on Highway 78. A disjunct collection is from a few miles northeast of Globe, Gila County. Documented elevational range in Arizona is about 1167-1634 m. The species is found from southeastern Arizona east to central Texas, and from eastern Sonora eastward through the Chihuahuan Desert of Chihuahua and Coahuila, and south to San Luis Potosí and Zacatecas. In Sonora, it is only known from two records: one from Plains grassland at Cananea, and a second from 1821 m in pine-oak woodland to the west of Yécora.

This is often thought of as a species of the Chihuahuan Desert in valleys and bajadas, and it certainly occurs in those situations in Arizona, but it is also frequently found in semi-desert grassland, occasionally in Plains grassland, and in oak woodland or savanna in the mountains. The high elevation record is from an area of oak woodland in the rugged terrain of Big Casa Blanca Canyon in the Santa Rita Mountains. The Gila County record is from an area of transition from semi-desert grassland to inland chaparral. Swann and Schwalbe (2007) found the Chihuahuan Hook-nosed Snake in grasslands at Coronado National Memorial during 1997-98, but surveyors failed to find it there in 1978. They postulated that the grasslands had recovered from previous overgrazing, favoring the Chihuahuan Hook-nosed Snake and other grassland species.

The Gila County collection suggests this species may have been overlooked in the northern portions of the Circle. Mead et al. (1984) described a fossil collection of this species from Deadman Cave on the northeastern slope of the Santa Catalina Mountains (1400 m) dating to 8,000-12,000 years before present. That locality is between the Gila County and more southern localities; the species could potentially still occur there.

In Arizona, most of these snakes are found at night on roads; however, they are sometimes encountered surface active during the day. One was observed just after noon at 1587 m elevation in the Santa Rita Mountains. The upturned snout suggests a burrowing habit. Degenhardt et al. (1996) say that rocks and loose soils are used for cover and burrowing. Tennant (1998) stated they can be found under rocks in Texas.

In a sample of 20 Chihuahuan Hook-nosed Snakes, the smallest mature male was 170 mm SVL and the smallest mature female was 237 SVL; however, the author stated that determining minimum size at maturity for females was hampered by small sample size (n=6) (Goldberg 2002). Males produce sperm from June into September, and females lay 1-4 eggs in June or July. Not all adult females reproduce each year (Hardy 1975, Degenhardt et al. 1996, Goldberg 2002).

Food items documented in the wild include spiders, scorpions, and centipedes. Captives have also taken small snakes, lizard eggs, rat parts, newborn mice, and raw meat (Degenhardt et al. 1996, see review in Ernst and Ernst 2003). This snake has enlarged, grooved teeth in the rear of the upper jaw that likely serve to deliver salivary toxins to prey items (Ernst and Ernst 2003).

This species will often strike with its mouth closed when captured. It also practices cloacal popping when first touched. The cloacal lining is everted, resulting in a bubbling or popping noise. A battle between a Ring-necked Snake (Diadophis punctatus) and a Chihuahuan Hook-nosed Snake was observed in Big Bend National Park (Degenhardt et al. 1996), and Painter et al. (2012) found remains of a Chihuahuan Hook-nosed Snake in the stomach of a Kit Fox from Roswell, New Mexico. Dennis Caldwell found a Chihuahuan Hook-nosed Snake in the stomach of a bullfrog at Las Cienegas National Conservation Area.

The Chihuahuan Hook-nosed Snake is listed as a species of least concern on the 2014 IUCN Red List. With a valid Arizona hunting license, four can be collected per year or held in possession, alive or dead, except that collection is prohibited without special authorization in protected areas such as National Park Service units and National Wildlife Refuges. Swann and Schwalbe’s (2007) suggestion that this species declines in heavily-grazed areas may be true, but the paucity of records and the fact that this species occurs in a variety of vegetation communities makes it difficult to prove (e.g. Mendelson and Jennings 1992).

Chihuahuan Hook-nosed Snake (Gyalopion canum)

Description

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