size and symmetry of these append-
ages is such to cast serious doubt on
this hypothesis in my opinion.
Furthermore, many of these snakes
are endowed with cryptic colours and
patterns, and are effectively concealed
amongst leaf litter on the forest floor,
or, in the case of many desert
viperids, by almost completely bury-
ing themselves in sand. If enlarged
supraorbital or nasal scales functioned
purely to break up the creatures’
outlines, surely this would render
them superfluous.
blown by the wind will invariably
bank up against any exposed object
rather than flow around it, and in any
case, although snakes lack eyelids,
their eyes are protected by a special
transparent scale, or brille. A variation
on the ‘sand hypothesis’; that the
supraorbital spines may contribute to
both concealment and visibility by
facilitating a build up of sand above
the eyes but prevent it getting into the
eyes themselves, seems more appeal-
ing. It is a tantalising fact that horned
vipers from sandy habitat are more
likely to have supraorbital protuber-
ances than those from stony terrain.
spp. are alone in the sexual dimor-
phism of their facial protuberances).
Traditionally (along with their thin
build and sombre colouration), these
nasal extensions have been assumed
to assist the snakes to mimic vines or
branches. In this instance, the relative
size and shape of these appendages is
undoubtedly sufficient for this to be a
factor. Prey items, in the form of
small lizards, are actively stalked, and
typically remain oblivious to the
snakes’ presence. Lateral head sway-
ing is used while stalking, and this is
believed to enhance visual acuity in
For desert-dwelling species, it has
other arboreal snakes. Furthermore,
been speculated that supraocular
based upon behavioural studies, it has
projections may shade the eyes or
If all these theories seem to be getting been postulated that the elongated
protect them from drifting grains of
nowhere fast, perhaps the best clues
snout serves as an extension of the
sand. Presumably, this theory could
as to the function of these apparatus
eye-line and a point of reference
be extended to nasal horns, which
stem from research into two unusual
during stalking – in a similar manner
may prevent sand from entering the
and far-flung species of colubrids.
to the rigid tongue thrusting exhibited
nares. One line of thought is that
The Madagascar Leaf-nosed Snake
by Ahaetulla spp. and Oxybelis spp.,
supraorbital horns are bent down-
(Langaha madagascariensis) is a
amongst others – resulting in
wards to shield the eyes while the
small arboreal serpent endemic to the increased precision of strikes.
snakes lie partially submerged.
island of Madagascar. There is signifi-
Similarly, enlarged supraorbital scales cant sexual dimorphism; males being South-east Asia’s Tentacled Snake
have been postulated to protect
brown above, with a yellowish ventral (Erpeton tentaculatum) has eccentric
snakes’ eyes as they move through
surface, whereas females are a mot-
nasal projections that fulfil a very
dense undergrowth. However, there is tled grey in colour. Additionally,
different purpose. These aquatic
no real evidence to support this
females possess an exaggeratedly
snakes are specialist ambush hunters
conjecture, and the size and shape of elongated, leaf-shaped, laterally-
of fish and will wait motionless in a
the projections would again appear to compressed snout, while that of the
characteristic ‘J’ shape for prey to
mitigate against it. In addition, sand
male is tapering and pointed (Langaha venture close enough to deploy a