Heloderma suspectum - Cope, 1869
Gila Monster
Taxonomic Status: Accepted
Related ITIS Name(s): Heloderma suspectum Cope, 1869 (TSN 174113)
Unique Identifier: ELEMENT_GLOBAL.2.103164
Element Code: ARACE01010
Informal Taxonomy: Animals, Vertebrates - Reptiles - Lizards
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Reptilia Squamata Helodermatidae Heloderma
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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Concept Reference: Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.
Concept Reference Code: B90COL01NAUS
Name Used in Concept Reference: Heloderma suspectum
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 24Jun2005
Global Status Last Changed: 23Oct1996
Rounded Global Status: G4 - Apparently Secure
Reasons: Occurs in the southwestern U.S. and northwestern Mexico; fairly common in some areas; some habitat has been lost to agriculture and urbanization, and illegal collecting may limit certain local populations, but the species is apparently secure at the present time.
Nation: United States
National Status: N4 (21Oct1996)

U.S. & Canada State/Province Status
United States Arizona (S4), California (SNR), Nevada (S2), New Mexico (S3), Utah (S2)

Other Statuses

IUCN Red List Category: NT - Near threatened
Convention on International Trade in Endangered Species Protection Status (CITES): Appendix II

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: The Gila monster ranges from extreme southwestern Utah, southern Nevada, and adjacent southeastern California south through southern Arizona, southwestern New Mexico, and much of Sonora to Sinaloa, Mexico (Stebbins 2003). The core of the range is in Arizona and Sonora. Elevational range extends from near sea level in Sonora and 30 m in Arizona to at least 1,545 m in southeastern Arizona (Lowe et al. 1986); 1,180-1,950 meters in New Mexico (Degenhardt et al. 1996).

Number of Occurrences: 21 - 300
Number of Occurrences Comments: This species is represented by well over 100 collection/observation sites that are well distributed throughout the range (e.g., see Campbell and Lamar 2004). Degenhardt et al. (1996) mapped approximately 17 collection sites in New Mexico (Campbell and Lamar 2004 mapped only 5); these represent several relatively distinct occurrences. The easternmost locations may represent displaced, released, or escaped captive individuals (Degenhardt et al. 1996).

Population Size: Unknown
Population Size Comments: Total adult population size is unknown but probably is at least several thousand; the species is fairly common in at least some parts of the range. Lowe et al. (1986) stated that Gila monsters are infrequently seen but not rare or uncommon in Arizona. In New Mexico, the species is commonly encountered in the Redrock Wildlife Area in Grant County and at Granite Gap in Hidalgo County; a density of approximately 5 individuals per square kilometer was estimated for one area (Degenhardt et al. 1996).

Number of Occurrences with Good Viability/Integrity: Unknown

Overall Threat Impact: Medium
Overall Threat Impact Comments: Populations have been exploited (illegally) by commercial and private collectors, and they have suffered from habitat destruction due to urbanization and agricultural development (New Mexico Department of Fish and Game 1985). Concrete-lined canals are barriers to movement (Brown and Carmony 1999), as are busy highways. Mortality on roads likely is increasing as traffic volume increases on established highways and new roads are built. The most important reason for the decline is habitat loss resulting from development (Campbell and Lamar 2004).

Short-term Trend: Unknown
Short-term Trend Comments: Populations are declining over most of the range (Campbell and Lamar 2004), but the rate of decline is unknown.

Long-term Trend:  
Long-term Trend Comments: Beck (1985) estimated that the population in Utah included 450-800 individuals, down from an estimated 2,000-5,000 before the 1930s.

Intrinsic Vulnerability: Moderately vulnerable

Other NatureServe Conservation Status Information

Protection Needs: Stringent prohibitions against commercial explitation and unnecessary killing should be maintained.

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) The Gila monster ranges from extreme southwestern Utah, southern Nevada, and adjacent southeastern California south through southern Arizona, southwestern New Mexico, and much of Sonora to Sinaloa, Mexico (Stebbins 2003). The core of the range is in Arizona and Sonora. Elevational range extends from near sea level in Sonora and 30 m in Arizona to at least 1,545 m in southeastern Arizona (Lowe et al. 1986); 1,180-1,950 meters in New Mexico (Degenhardt et al. 1996).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AZ, CA, NM, NV, UT

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.

Range Map Compilers: NatureServe, 2005


U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Cochise (04003), Gila (04007), La Paz (04012), Maricopa (04013), Mohave (04015), Pima (04019), Pinal (04021), Yavapai (04025), Yuma (04027)
CA Imperial (06025)*, Inyo (06027)*, Riverside (06065)*, San Bernardino (06071)*
NM Dona Ana (35013)*, Grant (35017)*, Hidalgo (35023)*
NV Clark (32003), Lincoln (32017), Nye (32023)
UT Washington (49053)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
13 El Paso-Las Cruces (13030102)+*
15 Lake Mead (15010005)+, Grand Wash (15010006)+, Hualapai Wash (15010007)+, Upper Virgin (15010008)+, Fort Pierce Wash (15010009)+*, Lower Virgin (15010010)+, White (15010011)+, Muddy (15010012)+, Meadow Valley Wash (15010013)+, Detrital Wash (15010014)+, Las Vegas Wash (15010015)+, Havasu-Mohave Lakes (15030101)+, Piute Wash (15030102)+, Sacramento Wash (15030103)+, Imperial Reservoir (15030104)+*, Bouse Wash (15030105)+, Tyson Wash (15030106)+, Lower Colorado (15030107)+*, Yuma Desert (15030108)+, Big Sandy (15030201)+, Burro (15030202)+, Santa Maria (15030203)+, Bill Williams (15030204)+, Upper Gila-Mangas (15040002)+*, Animas Valley (15040003)+*, San Simon (15040006)+*, San Carlos (15040007)+, Middle Gila (15050100)+, Lower San Pedro (15050203)+, Upper Santa Cruz (15050301)+, Rillito (15050302)+, Lower Santa Cruz (15050303)+, Brawley Wash (15050304)+, Upper Salt (15060103)+, Tonto (15060105)+, Lower Salt (15060106)+, Lower Verde (15060203)+, Agua Fria (15070102)+, Hassayampa (15070103)+, Centennial Wash (15070104)+, Lower Gila (15070201)+, Rio Sonoyta (15080102)+*, San Bernardino Valley (15080302)+
16 Dry Lake Valley (16060009)+*, Ivanpah-Pahrump Valleys (16060015)+
18 Upper Amargosa (18090202)+, Death Valley-Lower Amargosa (18090203)+*, Mojave (18090208)+*, Southern Mojave (18100100)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A large, stout lizard with beadlike scales.
General Description: A large, heavy-bodied lizard with a massive head, short thick tail (thin in emaciated individuals), beadlike dorsal scales, short limbs with strong claws, and loose folds of skin on the neck; dorsal coloration gaudy, black and pink, orange, or yellow; adult snout-vent length 22-35 cm (Stebbins 1985). Occasionally exceeds 50 cm in total length (Campbell and Lamar 1989, which see for further description details).
Diagnostic Characteristics: Differs from other U.S. lizards in large size and bulk, beadlike dorsal scales, and bold dorsal pattern of black and yellow, orange, or pink. Differs from the similar H. HORRIDUM of Mexico as follows: tail length less than 55% of snout-vent length (vs. at least 65%); 48-62 scales in longitudinal midline from vent to tip of tail (vs. 74-87); dorsal coloration includes yellowish, orange, or pink (vs. black with or without yellow). See Campbell and Lamar (1989) for further details.
Reproduction Comments: In southern Arizona, sperm formation occurs in May-June; females have oviductal eggs from late June into August (Goldberg and Lowe 1997). Eggs are laid primarily in July-August. Clutch size averages about 6, ranges up to 13 (Goldberg and Lowe 1997). In Arizona, eggs reportedly overwinter underground and hatch the following late April-early June, after an incubation period of about 10 months (Lowe et al. 1986, Goldberg and Lowe 1997). Females are sexually mature at about 24 cm SVL; mature females evidently reproduce every year (Goldberg and Lowe 1997).
Ecology Comments: Basically solitary but may use communal overwintering sites.
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: May migrate locally (usually less than 1 km) between highland winter retreat and lowland summer habitat (Lowe et al. 1986).

May travel up to several hundred meters in one day but typically much less. In northwestern Arizona, moved an average of 26 m per day in April-May, 3 m per day in June-July (Jones 1983). In Utah, 27 individuals (including only one immature) were observed in an area of 2 sq km over 3 years; home ranges of 3 individuals were 66, 33, and 6 ha (Beck 1990). In New Mexico, home ranges of 7 individuals ranged from 6 to 105 ha (mean 58 ha), were up to at least 3.5 km long (Beck and Jennings 2003).

Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Desert, Shrubland/chaparral, Woodland - Hardwood
Special Habitat Factors: Burrowing in or using soil, Fallen log/debris
Habitat Comments: Occupied vegetation types include desert grassland, Mohave and Sonoran desert scrub, and thorn scrub (Sonora); less often oak or pine-oak woodland. In Mexico, it occurs on lower mountain slopes and adjacent plains and beaches (Stebbins 2003), sometimes in irrigated areas. Canyon bottoms, arroyos, and rocky slopes may support relatively dense populations in some parts of Arizona and Sonora. In southern Arizona, the Gila monster is more abundant in wetter and rockier palo verde-sahuaro desert than in drier and sandier creosote-bursage desert, where it occurs mainly in or near rocky buttes or mountains (Lowe et al. 1986). In New Mexico, the species is most commonly associated with desert scrub vegetation in rocky regions of mountain foothills and canyons; sometimes it is found along the lower fringes of pinyon-juniper woodland or oak woodland; rarely encountered in agricultural areas (Degenhardt et al. 1996). Gila monsters are mainly terrestrial but infrequently climb into vegetation. Refuges include spaces under rock, dense shrubs, burrows, or woodrat nests. Sub-surface shelters are important components of the habitat, and certain ones are used with a high degree of fidelity (particularly in winter), sometimes by multiple individuals concurrently (Beck and Jennings 2003). In Arizona, Gila monsters spend about 98% of the year under cover (Lowe et al. 1986). In Utah, individuals spent over 95% of active season underground; occasionally they basked near shelters in spring; shelters were burrows or crevices in rocky areas; hibernacula faced south (Beck 1990).
Adult Food Habits: Carnivore, Invertivore
Immature Food Habits: Carnivore, Invertivore
Food Comments: Eats small mammals, eggs (especially of ground-nesting birds, also of reptiles), lizards, insects, and carrion. In northwestern Arizona in April-May, ate mainly eggs of ground-nesting birds; in June-July, diet apparently shifted to small mammals (Jones 1983). Ate eggs and young mammals taken from nests in Utah (Beck 1990). Two juveniles salvaged in Arizona contained reptile eggshells (McGurty 2002). Prey is detected mainly by olfaction.
Adult Phenology: Crepuscular, Diurnal
Immature Phenology: Crepuscular, Diurnal
Phenology Comments: In Arizona and Utah, active mainly from early spring through early fall (surface activity peaks in spring in Arizona); some may bask in winter. In summer, crepuscular-nocturnal or relatively inactive. In northwestern Arizona, relatively inactive (in rodent burrows) in June-July (Jones 1983). Often encountered on roads at dusk or after dark following warm summer rains (Stebbins 1985). In Utah, activity peaked between late April and mid-June, from 0800-1200 h; some nocturnal activity may occur in summer (Beck 1990).
Length: 61 centimeters
Economic Attributes
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Economic Comments: Venomous; one of two venomous lizards worldwide; see Ernst (1992) and Lowe et al. (1986) for information on effects of bites on humans.
Management Summary
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Management Requirements: Translocation of individuals away from urban locations does not appear to be an effective conservation tool. In Arizona, individuals that were moved less than 1,000 m from the site of capture returned within 30 days, whereas those translocated farther incurred a high mortality rate (Sullivan et al. 2004).
Population/Occurrence Delineation
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Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy highway or highway with obstructions such that lizards rarely if ever cross successfully; major river, lake, pond, or deep marsh; urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Gila monsters may travel up to several hundred meters in one day but typically much less. In northwestern Arizona, individuals moved an average of 26 m per day in April-May, 3 m per day in June-July (Jones 1983). In Utah, home ranges of 3 individuals were 66, 33, and 6 ha (Beck 1990). In New Mexico, home ranges of 7 individuals ranged from 6 to 105 ha (mean 58 ha) (Beck and Jennings 2003). Lowe et al. (1986:13) stated that annual home range size tends to be less than 1 kilometer in maximum dimension, but Beck and Jennings (2003) mapped several home ranges that were larger than this (up to about 3.5 km long).

The separation distance of 10 km for suitable habitat is approximately three times the diameter of a large home range.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 2 km
Date: 08Oct2003
Author: Hammerson, G.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 24Jun2005
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 23Jun2005
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Beck, D. D. 1985. The natural history, distribution, and present status of the gila monster in Utah. Department of Biology and Ecology Center, Utah State University, Logan, Utah. Report submitted to Utah Division of Wildlife Resources.

  • Beck, D. D. 1990. Ecology and behavior of the Gila monster in southwestern Utah. J. Herpetol. 24:54-68.

  • Beck, D. D. 2005. Biology of Gila monsters and beaded lizards. University of California Press, Berkeley. 256 pp.

  • Beck, D. D., and R. D. Jennings. 2003. Habitat use by Gila monsters: the importance of shelters. Herpetological Monographs 17:111-129.

  • Behler, J. L., and F. W. King. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp.

  • Brown, D. E., and N. B. Carmony. 1999. Gila monster: facts and folklore of America's Aztec lizard. University of Utah Press, Salt Lake City. 129 pp.

  • Campbell, J. A., and W. W. Lamar. 1989. The venomous reptiles of Latin America. Comstock Publ. Associates, Division of Cornell Univ. Press, Ithaca, New York. xii + 425 pp.

  • Campbell, J. A., and W. W. Lamar. 2004. The venomous reptiles of the Western Hemisphere. 2 volumes. Cornell University Press.

  • Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.

  • Crother, B. I. (editor). 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Sixth edition. Society for the Study of Amphibians and Reptiles Herpetological Circular 37:1-84. Online with updates at: http://www.ssarherps.org/pages/comm_names/Index.php

  • Crother, B. I. (editor). 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 7th edition. SSAR Herpetological Circular 39:1-92.

  • Degenhardt, W. G., C. W. Painter, and A. H. Price. 1996. Amphibians and reptiles of New Mexico. University of New Mexico Press, Albuquerque. xix + 431 pp.

  • Ernst, C. H. 1992. Venomous reptiles of North America. Smithsonian Institution Press, Washington, D.C. ix + 236 pp.

  • Goldberg, S. R., and C. H. Lowe. 1997. Reproductive cycle of the Gila monster, HELODERMA SUSPECTUM, in southern Arizona. Journal of Herpetology 31:161-166.

  • Jones, K. B. 1983. Movement patterns and foraging ecology of Gila monsters (HELODERMA SUSPECTUM Cope) in northwestern Arizona. Herpetologica 39:247-253.

  • Lowe, C. H., C. R. Schwalbe, and T. B. Johnson. 1986. The venomous reptiles of Arizona. Arizona Game and Fish Department. ix + 115 pp.

  • McGurty, B. M. 2002. Heloderma suspectum: egg predation by juveniles. Herpetological Review 33:205.

  • New Mexico Department of Game and Fish. 1985. Handbook of species endangered in New Mexico.

  • Stebbins, R. C. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.

  • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. Third edition. Houghton Mifflin Company, Boston.

  • Sullivan, B. K., M. A. Kwiatkowski, and G. W. Schuett. 2004. Translocation of urban Gila monsters: a problematic conservation tool. Biological Conservation 117:235-242.

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