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Higher TaxaColubridae, Colubrinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common Names 
DistributionDemocratic Republic of Congo (Katanga [Zaire])

Type locality: Mulisi, Nzovu Est, Kahuzi-Biega National Park (02.447291° S, 28.2825378° E, 1101 m), South Kivu Province, DRC.  
TypesHolotype. UTEP 22196 (field number MUSE 10341; Fig. 10), adult male, collected by Guillain M. Mitamba, Deo Kujirakwinja, Emmanuel Muhindo, Radar Nushili, Wandege M. Muninga, and Andrew J. Plumptre on 13 November 2015.
Paratypes. UTEP 22195 (field number EBG 1362; Figs. 1B, 9C), adult female collected in the vicinity of Irangi (01.8780° S, 28.4524° E, 811 m), South Kivu Province, DRC, collected from a tree by a resident and brought to Maurice Luhumyo, Chifundera Kusamba, Mwenebatu M. Aristote, Wandege M. Muninga, and Eli Greenbaum on 30 August 2007; RBINS 2698 (formerly RBINS 8621) (field no. Leloup #27), adult male from Bunyakiri (2.075630° S, 28.573194° E, 1000 m), South Kivu Province, DRC, collected by Paul Leloup on 6 March 1958. 
DiagnosisDiagnosis. A species of Toxicodryas restricted to east-central and East Africa (east of the confluence of the Congo and Ubangi rivers), defined by the following combination of characters: maximum SVL > 1 meter (vs. maximum SVL < 1 meter in T. pulverulenta and T. adamanteus sp. nov.); DSRN 23–29 (vs. 19–21 in T. pulverulenta and 18–23 in T. adamanteus sp. nov.); DSRM 21–25 (vs. 19–21 in T. pulverulenta and 18–21 in T. adamanteus sp. nov.); cloacal plate divided or undivided (vs. usually divided in T. blandingii, and always undivided in T. pulverulenta and T. adamanteus sp. nov.); adult males glossy or velvety black with a yellow venter, and adult females light brown, gray, or yellowish-brown with light-brown or cream cross-bars on the flanks, with yellowish-brown venters (vs. both sexes brown to pink with darker cross-bars that often enclose a whitish spot, and the dorsum and venter sprinkled with fine dark brown or black spots in T. pulverulenta and T. adamanteus sp. nov.); hemipenis relatively short and massive (i.e., broad), proximal third covered with spines, distal two-thirds dimpled with a flattened apex (vs. relatively long with long spines mid-way along the shaft that decrease in size towards the apex and base, and with a domed apex in T. pulverulenta and T. adamanteus sp. nov.); venom toxicity LD50 = 4.88 mg/kg in mice (vs. venom toxicity LD50 = 2.85–3.55 mg/kg in mice for T. blandingii) (Greenbaum et al. 2021).

Coloration (in life) of the holotype. Solid black over the entire length of the dorsum, and black ventrally except for the anterior half of the body, where the ventral scales are pale yellow with a black posterior edge that increases in thickness in correlation with increased distance from the head. The head is black dorsally and laterally except for yellow on the lower, anterior region of the 5th–9th supralabials, and yellow ventrally except for thin black rims on the posterior edges of the infralabials (Greenbaum et al. 2021).

Variation. For years, the size record for this species was attributed to Goodman (1985), who recorded a total length of 2515 mm for an adult female collected in Uganda. However, Hedges (1983:20) measured a specimen from Kenya that was 2707 mm total length, and said it “is reputed to exceed 3300 mm.” Weinstein et al. (2011) noted the species may exceed 3.5 meters. Spawls & Branch (1995, 2020) listed the maximum size as “about 2.8 m” (no specific location provided), but Weinstein (pers. comm.) estimated a captive specimen from Kakamega was approximately 3.0 meters total length.
Schmidt (1923:104) remarked that two specimens from DRC had fused prefrontals, creating a single transverse scale. Five of his 20 DRC specimens had a divided cloacal plate, “with indications of a groove in two others,” and as a result, he stated that the condition of the cloacal plate is “obviously useless” as a diagnostic character. Laurent (1956) noted that, with the exception of DRC specimens from Mayombe (north of the Congo River in Kongo Central Province and thus attributable to T. blandingii as recognized herein) with consistently divided cloacal plates, 13 of 31 snakes from other areas of DRC had an undivided cloacal plate. Our examined specimens confirm this sentiment, because 17/92 specimens have a divided cloacal plate, and an additional five specimens have a partially divided cloacal plate. Hellmich (1957b) noted maximum sizes of Angolan males (1740 mm SVL; 523 mm TL) and females (1730 mm SVL; 505 mm TL), and aberrant individuals that had 11 supralabials and 9–14 infralabials. De Witte (1966) noted that the species has 17 scale rows at midbody, but this datum is so aberrant that it is likely an error (Pitman 1974; Table 1). Skinner (1973) provided ranges of scale counts (161–274 ventrals, 86–147 subcaudals) that are so aberrant that they are clearly erroneous (at least for lower counts), and noted a maximum length of about 3 meters. For Uganda snakes, Pitman (1974) listed ventral scale counts from 240–260 (males) and 240–259 (females). De Witte (1975) noted a single individual with 25 scale rows at midbody, and Broadley et al. (2003) also noted 25 scale rows as the maximum amount of variation. Based on two specimens from Lukolela, Belgian Congo (AMNH 45907) and Akenge, Belgian Congo (AMNH 12243), Bogert (1940:61) described their maxillary teeth as “ten in number, followed after a short diastema by three enlarged, grooved fangs, the posterior one of which is smaller than the other two.”
Schmidt (1923:105) described two color phases of DRC specimens, including (1) a black phase with the anterior portion of the venter yellow, each ventral scale bordered with black on its posterior edge, the border increasing in width until the yellow color disappears on the posterior two-thirds of the venter; and (2) a brownish phase, “with more or less distinct wide dark cross-bars, confluent anteriorly, alternate posteriorly on the vertebral line.” Pitman (1938:211) described an unsexed individual from Uganda as “darkish gunmetal with a purplish mottling towards the tail, belly pale yellow from head to tail but with slight brown markings on the posterior half increasing in occurrence towards and on the tail.” A female from Uganda was described as rich chestnut dorsally and ventrally, with handsome chocolate blotches on the flanks, each one containing a small white spot. On the posterior part of the body, including most of the tail, these blotches were confluent with pale edging. The ventral aspect of the head and the first 50 ventrals were “paly yellowish tinged green.” The dorsum of the head was dark brown, and the posterior supralabials were dull greenish grey. The supralabials had black edging posteriorly, except for the last one. There were two elongated dark brown blotches behind the eye, which was iridescent hazel.
Bogert (1940:61) provided data for a specimen (AMNH 45907; determined to be a subadult male based on photographs examined by EG) that had been described by James P. Chapin as “olive-brown, with dark brown patches; below grayish brown.” Hellmich (1957b) described the coloration of several individuals from Angola, including an adult male that had a blue-reddish-black dorsum with a venter that was pale yellow in the front half of the body, with an ever-widening blue-black border that eventually enclosed the entire ventral scales towards the posterior side. Another adult male had a dark black-brown dorsum, and light yellow venter on the first third of the body, but starting on the 5th ventral, there was a dark gray-blue spot that increased in size posteriorly until it covered the entire venter towards the posterior end of the body. An adult female’s dorsum was described as clay yellow with mostly alternating dark transverse bars and a pale yellow venter. A second adult female had similar coloration to the latter specimen, but the transverse bands were only faintly visible on the posterior sixth of the body and tail. A juvenile dorsum was described as gray-brown with transverse black-brown spots that converge in the anterior part of the body, but then alternate posteriorly, with a light yellowish-white spot in the lower center of the spots.
Laurent (1956:195) listed a section about possible sexual dimorphism for this species, but stated that nothing glaring appears in his data. Pitman (1974:125) described several individuals from Uganda that were similar to the descriptions above, and added that both color phases “exhibit a handsome suede effect.” He noted that although subadult males might retain the brown phase, black females are unknown, and the black and brown color phases have “sexual significance.” The dark blotches of juveniles were noted to vary from “blackish, chocolate, reddish-brown or dark or bright chestnut,” with interspaces ranging from light gray, pale brown or chestnut, sometimes with a pinkish tinge. Goodman (1985:56) described two adult females from Uganda as “dingy olive-brown.” Hughes (2000) noted that Laurent (1964) seemed to imply that his largest male specimen from Dundo, Angola was not black, but this is not clear, because the latter author only mentioned in passing that a smaller male from Andrada, Angola represented the black phase. Spawls & Branch (1995, 2020) remarked that the yellow ventral pigmentation might form a stripe in the middle of the venter. In the brown color morph, the skin between the scales is bluish gray, and especially visible when the snake inflates its body during a threat display. The eye can be yellowish or brown. The black phase snakes are usually male, whereas the brown phase ones are usually female. Based on photos of an adult male from Banalia, DRC (individual shown in Fig. 9A), the base of the tongue is bluish black, and the forked tip is silvery gray (Greenbaum et al. 2021). 
CommentFor further references see Greenbaum et al. 2021 (not provided upon request). 
EtymologyThe specific epithet is a noun in apposition, invariable, from the Latin noun vexator, meaning harasser or stalker, in reference to the fact that this snake stalks prey when they are sleeping, and to its aggressiveness when disturbed. 
  • Greenbaum, E., Allen, K. E., Vaughan, E. R., Pauwels, O. S., Wallach, V. A. N., Kusamba, C., ... & Brown, R. M. 2021. Night stalkers from above: A monograph of Toxicodryas tree snakes (Squamata: Colubridae) with descriptions of two new cryptic species from Central Africa. Zootaxa 4965 (1): 1-44 - get paper here
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