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Desert Nightsnake (Hypsiglena chlorophaea)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2133″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Desert Night Snake, ©2013 Dancing Snake Nature Photography[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2555″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Desert Nightsnake (Cochise Clade), Cochise Co, AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2556″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake, Maricopa Co., AZ.. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2557″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake, Photo by Jerry Schudda[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2558″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake (Cochise Clade), Rancho El Aribabi, Sonora. Photo by Jim Rorabugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2559″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake (Cochise Clade), Western Dragoon Bajada, Cochise Co., AZ. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2560″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake eating Western Whiptail, Tucson Mountains © 2007 Howard Byrne III / ASDM Sonoran Desert Digital Library[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2561″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Desert Nightsnake, Photo by Young Cage[/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 systematics of Hypsiglena baffled herpetologists for decades.  In the 20^th century from one to five species were recognized within the genus. Today, based primarily on the work of Mulcahy (2008) and Mulcahy et al. (2014), Hypsiglena is known to consist of at least 10 species and numerous subspecies.  These are small (< 642 mm TL), slender snakes with vertically elliptical pupils, smooth dorsal scales in 17-21 rows, and dark blotches, spots or bands on the neck. Three species apparently occur in the 100-Mile Circle (Mulcahy 2008), although one of them (the “Cochise clade”) has yet to be described, and differences among the three are subtle.

The Desert Nightsnake (Hypsiglena chlorophaea) is small (< 642 mm TL) and slender, the smooth dorsal scales are in 21 rows at mid-body, the anal plate is divided, and the pupils are vertically elliptical.  One loreal scale is present on each side. This species possesses a dark neck collar that may be broken by one or two light stripes.  A dark elongated blotch or stripe on each side of the head extends downward and back from the eye and may join the neck collar.  The dorsum of the body and tail is tan or gray with 50-70 dark mid-dorsal blotches that often appear as two adjoining rows of offset blotches. There are smaller, dark lateral blotches.  The venter is white or cream and unmarked.  Females grow to a longer SVL, but males have proportionally longer tails.

This species can easily be confused with the Chihuahuan Nightsnake (Hypsiglena jani) and an undescribed species referred to as the “Cochise clade” or the Hooded Nightsnake (see Mulcahy 2008).  The former has three neck blotches, the two lateral blotches connect with the dark eye stripes and are elongated towards the rear.  The center blotch extends anteriorly as a narrow dark line to the parietal scales. The lateral and central blotches may or may not be joined at their edges.  Dark blotches on the body are relatively large and mostly in a single row, although some paired, offset blotches may be present, and those may be fused or not.  Hooded Nightsnakes have a single neck blotch that is rounded posteriorly and narrows on the dorsum.  It extends anteriorly along the mid-dorsal line as a dark stripe.  The eye stripe narrows to a point where it meets the neck blotch.  Hooded Nightsnakes also have two rows of small dark, offset blotches on the dorsum, some of which may be fused (Mulcahy 2008).  Problems arise, though, in identification because of individual variation.  For instance, in the image gallery, the snake from Maricopa County, clearly within the range of chlorophaea, has a single neck blotch and two rows of offset, small blotches.  Until it is formerly described, the Hooded Nightsnake is treated herein as part of Hypsiglena chlorophaea.  

These snakes are widely distributed within the 100-Mile Circle below about 1830 m in Sonoran desertscrub, Chihuahuan desertscrub, and semi-desert grassland. They are less frequently found in Plains grassland, oak woodland, and pine-oak woodland, and are more common in the Arizona Upland Subdivision as compared to the Lower Colorado River Subdivision of Sonoran desertscrub.  They are probably most abundant on bajadas, but can be found on rocky slopes and in valley bottoms, as well (Brennan and Holycross 2006, Rorabaugh and Lemos-Espinal 2016).  The distribution of the species, as defined by Mulcahy (2008), includes portions of western and southern Arizona and most of western and southern Sonora.  In the Circle, the Desert Nightsnake is replaced by the Chihuahuan Nightsnake at the base of the Pinaleño Mountains (Mulcahy 2008).  The Hooded Nightsnake occurs to the south and east of Tucson, generally east of the Sonoran Desert.  It extends marginally into southwestern New Mexico. Mulcahy (2008) speculated that it also occurs in northeastern Sonora, but he had no specimens or tissues from that region.  The Nightsnake featured in the image gallery from Rancho El Aribabi, Sonora, appears to be of the Cochise clade.  The author has also seen Nightsnakes from Rancho Los Fresnos northwest of Cananea that appear to be of the Cochise clade.  At the geographic boundary of the Hooded Nightsnake and the Chihuahuan Nightsnake, Mulcahy (2008) noted snakes with genetic signatures of one species but pattern characteristics of the other.

Desert Nightsnakes have been collected every month of the year in the 100-Mile Circle except November, although most are found March-September.   As its name implies, it is mostly nocturnal, although individuals are occasionally found surface active during the day.  They are not uncommonly found under cap rocks or debris, or in rock crevices during the day.

Reproduction in the Desert Nightsnake has not been well studied; however, a female measuring 340 mm SVL and 396 mm TL collected from Santa Cruz County laid three eggs on July 15. Two of those hatched on 12 September and the hatchlings measured 157 and 192 mm TL.  Two other females within the range of H. chlorophaea had three and four enlarged follicles in June and July (Clark and Lieb 1973).  Hypsiglena typically have clutch sizes of 2-9 eggs (Ernst and Ernst 2003).

No comprehensive study of the diet of the Desert Nightsnake has been conducted.  However, Lance (2012) observed a Desert Nightsnake in the morning at Tohono Chul Park consuming an adult Zebra-tailed Lizard (Callisaurus draconoides).  Howard Byrne III photographed a Desert Nightsnake preying upon a Western Whiptail (Aspidoscelis tigris) in the Tucson Mountains (see image gallery). Tuijl-Goode (2008) watched a Desert Nightsnake consume a Banded Sandsnake (Chilomeniscus stramineus) at a Tucson golf course.  Another predation attempt of a Desert Nightsnake on a Banded Sandsnake was documented in South Mountain Park near Phoenix (Brennan 2004).  Predation of juvenile Great Plains Toads (Anaxyrus cognatus) by a Desert Nightsnake was documented by Enderson (2001) in the Vekol Valley, Maricopa County. Rodriguez et al. (1999) examined stomach contents of 178 H. “torquata” (which until the recent work of Mulcahy included all Hypsiglena in Arizona) and summarized the literature and unpublished observations of predation by this species, but they had data for only four Arizona specimens.  Nonetheless, they found no geographic variation in the diet of examined snakes.  The authors concluded that H. “torquata” primarily eats Sceloporine lizards and the eggs of lizards and snakes, but occasionally takes frogs, snakes, insects, and amphisbaenians.  The Desert Nightsnake has enlarged, ungrooved teeth in the rear of the upper jaw that help deliver neurotoxins and hemorrhagic compounds from a Duvernoy’s gland to prey items. Desert Nightsnakes chew their venom into the wound. These snakes virtually never bite when handled and are probably too small to deliver a venomous bite to humans. When harassed or threatened, a Desert Nightsnake will sometimes pull itself into a very tight coil with its head in the center.

The status of the Desert Nightsnake has not yet been evaluated by the IUCN. However, Hypsiglena torquata, from which the Desert Nightsnake was recently split, is listed as a species of least concern on the 2014 IUCN’s Red List. With a valid Arizona hunting license, 20 can be collected per day or possessed, alive or dead.  The Desert Nightsnake is eliminated from areas of urbanization and intensive agriculture, but there is no reason to believe it is declining in wild lands.

Suggested Reading:

Brennan, T.C. 2004. Hypsiglena torquata (nightsnake). Diet. Sonoran Herpetologist 17:30.

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Clark, D.R. Jr., and C.S. Lieb. 1973. Notes on reproduction in the night snake (Hypsiglena torquata). Southwestern Naturalist 18:248-252.

Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996.  Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.

Enderson, E.F. 2001. Predation and method of ingestion by a Desert Nightsnake (Hypsiglena torquata) on a Great Plains Toad (Bufo cognatus). Sonoran Herpetologist 14(2):14-15.

Ernst, C.H., and E.M. Ernst. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington, D.C.

Lance, K. 2012. An instance of diurnal predation by a Desert Nightsnake, Hypsiglena chlorophaea. Sonoran Herpetologist 25(10):99-100.

Mulcahy, D.G. 2008. Phylogeography and species boundaries of the western North American Night Snake (Hypsiglena torquata): revisiting the subspecies concept. Molecular Phylogenetics and Evolution 46:1095-1115.

Mulcahy, D.G., J.E. Martinez-Gómez, G. Aguirre-Léon, J.A. Cervantes-Pasqualli, and G.R. Zug. 2014. Rediscovery of an endemic vertebrate from the remote Isla Revillagigedo in the eastern Pacific Ocean: the Clarion Nightsnake lost and found. PLOS ONE 9(5):1-5.

Rodriquez-Robles, J.A., D.G. Mulcahy, and H.W. Greene. 1999. Dietary ecology of the desert nightsnake (Hypsiglena torquata). Copeia 1999:93-100.

Rorabaugh, J.C., and J.A. Lemos Espinal. 2016. A Field Guide to the Amphibians and Reptiles of Sonora, Mexico. ECO Herpetological Publishing and Distribution, Rodeo, New Mexico, USA.

Tuijl-Goode. R. 2008. Battle of the snakes. Sonoran Herpetologist 26(6):66.

Author:  Jim Rorabaugh

For more information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 2001 Feb:14-15; 2004 Mar:30; 2008 Jun:66; 2012 Oct:99-100.

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