Editor’s Note: In a genetics study, Myers et al. 2017 (Copeia 105(4):642-650) concluded that all New World racers and whipsnakes should be in the genus Masticophis except for Coluber constrictor.

Figure 1. Range of the three subspecies of Coachwhip (Coluber flagellum) in Arizona. Map by Thomas C. Brennan, www.reptilesofaz.org.

The Coachwhip, Coluber flagellum, is a fairly slender, smooth-scaled, fast-moving snake occurring in the deserts of the southwestern United States. In Arizona (Figure 1), there are three subspecies: Sonoran Coachwhip (C. f. cingulum; Lowe and Woodin 1954:247; Figure 2), Lined Coachwhip (C. f. lineatulus; Smith 1941:394; Figure 3), and Red Racer (C. f. piceus; Cope 1892:625; Figures 4 and 5).

These subspecies are differentiated mainly by color, color pattern, and geographic range. The Coachwhip was originally assigned to the genus Coluber by Shaw in 1802 (Figure 6), but was later switched to Masticophis (from Greek mastix meaning “whip” and ophis meaning “snake”; Ortenburger 1928). Nagy et al. (2004) hinted that the relationship between Masticophis and Coluber should be studied in closer detail, although their data could not conclusively combine the two genera. However, a year later Utiger et al. (2005) synonymized Masticophis with Coluber. A black “whip snake” in Arizona was originally known as Coluber flagellum frenatus (see King 1932), but was later determined to be a black morph of the Red Racer by Klauber (1942).

In one study of Coachwhips, snout to vent lengths (SVL) for six males and three nongravid females ranged from 67.7 to 106.3 cm (26.7 to 41.8 inches; mean 93.9 ± 2.7 cm [36.9 ± 1.1 inches]) and mass ranged from 115 to 256 g (4.1 to 9.0 oz; mean 173 ± 16 g [6.1 ± 0.6 oz]; Secor 1995). Eighty-one individual C. flagellum were examined during a dietary study and no sexual size dimorphism in SVL was detected; males = 83.1 ± 6.1 cm (32.7 ± 2.4 inches; range 33.0-165.0 cm [13.0-65.0 inches]), females = 80.6 ± 5.3 cm (31.7 ± 2.1 inches; range 37.5-152.0 cm [14.8-65.0 inches]), P = 0.73 (Halstead et al. 2008). Stebbins (2003) reported a total length range of 91 to 260 cm (36 to 102 inches).

The Coachwhip occurs in a variety of habitat types throughout the arid southwest. Habitats include creosotebush shrubland, mesquite dune habitats, and grasslands (Jones and Whitford 1989), as well as oak savannah (Johnson et al. 2007). Coachwhips also occur in sage scrub with a grassland component, riparian scrub, and fallow agricultural fields (Mitrovich et al. 2009) and in arid environments dominated with a variety of cacti species including Organ Pipe Cactus (Stenocereus thurberi; Hensley 1950), cholla (Opuntia fulgida and O. spinosior; Austin et al. 1972), and other species. Other habitats include prairie, juniper-grassland, woodland, and thornforest, but dense vegetation is generally avoided (Stebbins 2003). Coachwhips are known to travel up to 1 km (0.62 mi) within a 24-hr period, and therefore exhibit a pattern of long-distance movements, although these movements are not in a straight line and generally follow areas with the most cover (Johnson et al. 2007). Movements are likely influenced by prey distribution and abundance. Home range sizes did not differ between males and females in one study (Johnson et al. 2007). Average home range size was 70.4 ha (174 acres) in eastern Texas and 57.9 ha (143 acres) in the Mojave Desert (Johnson et al. 2007, Secor 1995).

Figure 2. Sonoran Coachwhip (Masticophis flagellum cingulum). Photo by Daniel M. Bell.

Coachwhips consume a variety of prey, with their staple being mainly lizards and other reptiles. Examples include Sidewinders (Crotalus cerastes; Secor 1995), horned lizards (Phrynosoma sp., Tyler 1977), Tiger Whiptails (Aspidoscelis tigris; McKinney and Ballinger 1966), and Common Side-blotched Lizards (Uta stansburiana; McKinney and Ballinger 1966), among many others (e.g., Sceloporus and scincids; Johnson et al. 2007). Some predatory encounters may be unsuccessful, such as when a Coachwhip attempted to take a Common Kingsnake (Lampropeltis getula; Repp 2002) or when death occurs as a result of attempting to consume species too difficult to swallow (i.e., Texas Horned Lizards, Phrynosoma cornutum; Sherbrooke 2008). Mammals and birds (nestlings and eggs) are also common prey species. Coachwhips consume Mexican Free-tailed Bats (Tadarida brasiliensis; Herreid 1962), Abert’s Towhees (Pipilo aberti; Finch 1981), House Finches (Carpodacus mexicanus; Swann 2004), and Cactus Wrens (Campylorhynchus brunneicapillus; Austin et al. 1972). Other dietary items include small mammals (rodents), frogs, toads, small turtles, insects, and carrion (Stebbins 2003). Cannibalism has also been observed in Coachwhips (Matos 2004).

Figure 3. Lined Coachwhip (Masticophis flagellum lineatulus). Photo by Erik F. Enderson.

The Coachwhip actively pursues its prey, as it is a fast-moving snake, and, with its large eyes, is thought to be a visual hunter (Secor 1995). There is evidence, however, that Coachwhips hunt by smell as well. In a clever experiment, researchers exposed naïve young Coachwhips to integumentary chemicals from several potential prey species, non-prey species, and distilled water and found that the hatchlings were able to discriminate between prey species and the controls, suggesting a genetic basis for prey species detection via odor (Cooper et al. 1990).

Figure 4. Red Racer (Masticophis flagellum piceus) from the Mojave Desert, Los Angeles County, CA. Photo by Howard Clark.

Secor (1995) also noted that Coachwhips are able to find prey through chemoreception.  A study animal was able to track a Sidewinder to a burrow using chemoreception. Secor (1995) also observed a Coachwhip, by using tongue-flicking, detect an adult Glossy Snake (Arizona elegans) beneath a sandy surface, and excavated it by using its head as a shovel. In addition to actively pursuing prey, Coachwhips were found to also be effective ambush predators (Jones and Whitford 1989). A Coachwhip was observed coiled around the stem of a mesquite bush and remained in the shade until a lizard came by. The snake then extended its head toward the lizard with the tail still attached to the mesquite stem. The snake was very successful in securing prey using this strategy. Coachwhips have skeletal muscle systems in their necks that facilitate an active-search strategy of capturing prey by allowing their head to be elevated while hunting. However, the sit-and-wait method described by Jones and Whitford (1989), depending on habitat structure and prey species composition, is an additional means of capturing prey. The sit-and-wait strategy seemed to be more common during the hotter summer months, where lizards often took refuge under shrubs to escape from high temperatures between shrubs. Coachwhips cryptically concealed under a shrub could therefore take advantage of shade-seeking prey, while at the same time being out of sight of other predators.

The Coachwhip typically emerges from hibernation by mid-March (see Kinney 1941) and during the first few weeks after emergence, surface activity is restricted to midday. During the night, the snake retreats to rodent burrows. In April, the Coachwhip gradually begins to increase activity to other parts of the day (Secor 1995). Throughout late spring and early summer, Coachwhips continue to expand their daytime activities to nearly a continuous level. During mid-summer, there is a split in activity, due to the higher temperatures (Secor 1995). Activity peaks occur during the late morning and late afternoon, while the lull during midday is spent in a burrow. By October, Coachwhips typically stop their two-peak activity pattern and begin decreasing their daytime activities until hibernation (Secor 1995). Coachwhips enter hibernation by mid- to late November and overwinter independent of conspecifics in rodent burrows (Secor 1995), however use of hibernacula has been documented with this species (Parker and Brown 1973).

Figure 5. Red Racer (Masticophis flagellum piceus). Photo by Erik F. Enderson.

Reproduction in the Coachwhip was studied in detail by Goldberg (2002). Reproductive tissue was examined from 145 sexually mature Coachwhip museum specimens collected from Arizona. Spermiogenesis in males is a seasonal testicular cycle, occurring from April to November (for scanning electron microscope photos of C. flagellum spermatozoa see Kofron 1980). Male Coachwhips collected from March to July and in December had regressed testes. Testes in recrudescence occurred in males collected from March to August. Females were typically reproductive from April to July. Clutch size for nine females ranged from 2 to 12 (mean = 7.2 ± 3.0). Here, Goldberg (2002) found a new minimum clutch size of 2 for the Coachwhip. The typical clutch size is reported as ranging from 4 to 20 (Stebbins 2003) but can be as high as 24 (Werler and Dixon 2000). Eggs are usually laid in June and July, with an incubation period of 76 to 79 days (Perkins 1952). Nest sites are usually established inside small mammal burrows in loose soil (Werler and Dixon 2000). Eggs are 2.5 to 3.8 cm (1 to 1.5 inches) long and hatch in August or September (Werler and Dixon 2000). Young measure 27.9 to 35.6 cm (11 to 14 inches) long (Werler and Dixon 2000).

The Coachwhip tends to be aggressive when handled, with bites to the handler being common, as well as emptying the contents of their cloaca. Sometimes it appears that the snake approaches people, but this may be because the snake was disturbed first and is simply eliciting an aggressive reaction.  See Repp 1998a and 1998b for descriptive details of aggressive Coachwhip behaviors. Additionally, if excessively handled, Coachwhips may play “dead” to avoid predation (Repp 2001, Gehlbach 1970). Another tactic commonly used to avoid predation is climbing into cacti, shrubs, and trees (Cunningham 1955). Coachwhips are excellent climbers and can leap from shrub to shrub in order to escape potential predators (See Repp 1998a, b, Werler and Dixon 2000).Coachwhips have several known predators. The most common are the Coyote (Canis latrans), Kit Fox (Vulpes macrotis), Raccoon (Procyon lotor), and predatory birds (Secor 1995, Johnson et al. 2007). Mortalities due to vehicles appear to be very common (Campbell 1956). Coachwhips have been known to live as long as 13 years, at least in captivity (Perkins 1955).

Figure 6. Description by Shaw (1802). Note that Shaw mentioned that Catesby
was the first describer for this species, but Shaw is given credit in the literature
as the first describer. Image by Howard Clark.

Coachwhips are known to harbor blood parasites. These include the blood protozoans, Hepatozoon serpentium (Hilman and Strandtmann 1960), Haemogregarina mansoni (Roudabush and Coatney 1937), and Karyolysus sp. (Wood and Wood 1936). Coachwhips also carry cestodes (Mesocestoides sp.; Conn and McAllister 1990), flatworms (Lechriorchis tygarti; Nelson 1950), and the coccidians Eimeria zamenis (Wacha and Christiansen 1974), Caryospora duszynskii, and C. masticophis (Upton et al. 1994). Three species of larval chiggers are known to parasitize Coachwhips: Euschongastia lacerta, Odontacarus shawi, and Trombicula arenicola (Powder and Loomis 1962).

The Coachwhip is an important member of the herpetofauna of the Arizonan desert landscape. Be sure to keep an eye out for this dynamic snake, taking note of its varied dorsal patterns within the 100-mile circle, and perhaps you will catch one in action hunting for a lizard, taking down another snake, or searching bird nests for hatchlings.