Unlimited by a legless lifestyle.
Climbing steep surfaces poses challenges for any animal:
the entire body weight must be continually lifted, in
addition to preventing slipping (and potentially fatal
consequences). Despite lacking grasping limbs, claws or
the adhesive toe pads present in other arboreal animals,
snakes from diverse lineages have independently evolved
to be remarkable climbers. Snakes use muscular gripping
forces to climb, as do primates, but have a distinct advan-
tage because their entire body can be used (rather than just
the hands, feet and sometimes the tail), enabling them to
grip branches spanning a wide range of diameters.
If snakes are climbing rough, relatively horizontal
surfaces with adequately-spaced irregularities, they can
shimmy up without needing to use their body for
additional grip. But when climbing smooth, steep,
cylindrical structures, snakes use a type of concertina
locomotion involving periodic static gripping: looping the
body around a branch one to three times, stretching
forwards, then looping around again and dragging the
lower part of the body up behind. This ‘friction-gripping’
concertina locomotion prevents slipping, but requires the
‘BOA CONSTRICTORS
have a ‘safety first’ policy, and are
the most SAFETY
CONSCIOUS of snakes. ’
application of considerable force, and involves a lot of
stop-starting. Energy expenditure is high, and progress is
relatively slow.
Given the energetic cost of using muscular forces to grip
inclined, cylindrical surfaces, and that snakes have consid-
erable control over the size and orientation of their grip,
one would expect some economisation in that a minimum
amount of exertion would be used. Yet a study in 2014
found that this was not the case; rather, snakes have a
policy of ‘safety first’ and will grip the substrate with a
safety factor often exceeding three. Of the five species
examined, Boa Constrictors, the species least specialised
for an arboreal existence, were the most safety conscious,
with safety factors of five recorded. Nevertheless, the
extra force may represent an overall energy saving, be-
cause it minimises the risk of slipping backwards, which
may be energetically costly given that any ground lost
must be recovered.