The Snakes of Europe

by George Albert Boulenger

Fig. 35 (after Sordelli)

Head-Shields.—Rostral as deep as broad or slightly broader than deep, rarely once and one-third as deep as broad, not or but scarcely visible from above. In addition to the supraoculars, three large shields, the frontal and the parietals, are as a rule present on the top of the head. Frontal as long as broad or a little longer than broad, rarely much longer than broad, once and a half to twice and a half as broad as the supraocular, from which it is as a rule separated by one to four shields, as long as or a little shorter than its distance from the rostral, as long as or a little shorter than the parietals. Parietals usually in contact with the frontal and separated from the supraoculars by small shields, but sometimes in contact with both, or separated from the frontal. Exceptionally, in specimens from Great Britain, Germany, and Austria, the parietals, or the frontal and the parietals, are broken up into scales, and this is more frequently the case in specimens from North-Western Spain (var. seoanei). Upper surface of snout bordered by six (rarely by five or four) small shields, viz., two apicals (rarely one), and on each side two canthals, the second of which is usually in contact with the supraocular; canthals very rarely united into one shield; the space between these shields covered by four to twenty flat or convex, juxtaposed scales, which very exceptionally are fused into a single large shield. Supraocular usually extending posteriorly beyond the vertical of the eye. Six to thirteen scales round the eye, usually eight to ten; two or three superposed scales, rarely two vertical series of scales, separate the preoculars from the nasal, which is single. As a rule a single series of scales intervenes between the eye and the labials; specimens with two series are of very exceptional occurrence (single specimens from Isle of Arran, Normandy, Southern Norway, and Carniola, in the British Museum), but there are occasionally two series except just below the centre of the eye. Upper labials six to ten, usually eight or nine; fourth or fourth and fifth (rarely third and fourth) below the eye. Temporal scales smooth, rarely feebly keeled. Three or four (rarely five) lower labials in contact with the single pair of chin-shields.

Scales in twenty-one (rarely nineteen or twenty-three) rows, with two apical pits, strongly keeled, those of the outer row smooth or feebly keeled. Ventral shields 132 to 150 (usually 137 to 147) in males, 132 to 158 (usually 140 to 150) in females; anal entire; subcaudals 32 to 46 (usually 35 to 40) in males, 24 to 38 (usually 28 to 33) in females.

Coloration.—It is characteristic of this species, contrary to the rule in snakes, to present such marked differences of colour, according to the sexes, that these can be distinguished in most cases from that character alone.

Whitish or pale grey specimens, with black belly and jet black dorsal markings ([Plate XII].), are males. Brown and brick-red specimens, with the markings of a more or less dark brown or red, are females. There are also brown, reddish-brown or olive males with the markings of a deep black, and grey males with brown markings. A very pretty colour variety, which affects only females, is olive with brick-red band and spots. Some males, just before exuviation, have the lower surface of a pale greyish-blue (Coluber cæruleus, Sheppard), with the outer ends of the shields black. Specimens with yellowish-white chin and throat, which may be tinged with red, are females; males have the throat black, or whitish with the scales spotted or edged with black. Exceptional females occur (in Carniola) which in this respect resemble the males.

The markings vary considerably. Those on the back usually consist of a wavy or zigzag longitudinal band, flanked on each side with a series of spots corresponding to its sinuses; but this band may be partly or even entirely broken up into rhomboidal or transversely oval spots, or, losing its indentations, form a straight stripe edged on each side with a yellowish streak (as in some specimens of the var. seoanei, from North-Western Spain). The markings may be absent altogether (var. concolor, Jan), or reduced to a narrow straight vertebral band (Pelias dorsalis, Gray). In the var. seoanei the zigzag band is often replaced by a dark brown vertebral band, three to five scales wide, bordered on each side by a series of subtriangular or crescentic black spots opposite to each other, as in the Pyrenean specimens of V. aspis. A pair of elongate dark markings are usually present on the back of the head, affecting the following shapes: |\,)(,)(,)(; By uniting together, this pair of markings may form a Λ or an X. An oblique dark streak extends on each side from the eye to the last labial shields, being sometimes prolonged a short way down the neck. The snout and vertex may be uniform or bear some symmetrical dark spots, or in some males be entirely black, the black involving the apex of the Λ-shaped marking. The labial shields are whitish or yellowish, those at least which are anterior to the eye being more or less broadly edged with brown or black.

The belly and the lower surface of the tail vary from grey or brown to bluish, blackish-grey, or black, the sides usually dotted or spotted with whitish; sometimes, especially in females, the belly is dark grey, each shield with a white posterior border which is broken up by a series of small roundish black spots. The end of the tail is often yellowish, bright yellow, or pale orange below, rarely coral red, more commonly in females than in males.

The iris is usually coppery red, more rarely golden suffused with brown.

Black specimens occur, more or less frequently, all over the habitat of this species, and are often referred to as V. prester, Linnæus. A distinction has to be made between individuals which are black through darkening of the ground colour, and such as are thus coloured through expansion and confluence of the markings. The latter are males, and among them we may find intermediate stages showing how this melanism is brought about; in one case the black of the back is separated from the black of the sides by a narrow light brown wavy stripe, the remains of the ground colour. When, as in all females, and occasionally in males, the black is the result of a gradual darkening of the ground colour, the typical markings may still be detected under certain lights. Some specimens (from Schneeberg, Lower Austria) are black, with scattered golden dots, or of a dark mahogany brown speckled with yellowish. In nearly all the black specimens at least a few dots of whitish are visible on the lips, and of yellow under the end of the tail.

Most of the variations enumerated above occur irrespective of the geographical distribution. Two forms, however, deserve to be regarded as ill-defined local races: the var. seoanei, Lataste, from North-Western Spain, in which, in addition to the peculiarities of coloration mentioned in the description, the canthus rostralis is frequently more distinctly raised, and the frontal and parietal shields are often disintegrated into scales; and the var. bosniensis, Boettger, from Bosnia, Carniola, and Carinthia, which is sometimes very suggestive of, and has been taken for, the typical form of V. aspis, having like it, though not at all constantly, two series of scales between the eye and the labials, and the zigzag band replaced by a series of dark bars across the back. The var. pseudaspis, Schreiber, from the plains of Sclavonia, described as straw yellow above, with narrow dark cross-bars, is hardly separable from the var. bosniensis.