Balling as a defence
mechanism for snakes
Raymond Hoser
488 Park Road
Park Orchards, Victoria, 3114, Australia.
E-mail: adder@smuggled.com
First published in hard copy
in Boydii (Journal of the Herpetological Society of Queensland), Spring
2005.
ABSTRACT
"Balling"
is a defensive mechanism for snakes.
This paper identifies (with examples) three uses, namely, 1/ To present
a shield from a predator, which to date is the most widely noted use of this
tactic. 2/ To escape a predator, either by rolling or avoiding detection due to
shape of the ball, or 3/ To retain heat
in extremely cold or rapidly cooling conditions.
INTRODUCTION
Coiling
in a ball is a common trait seen in snakes.
However until now there has been little thought as to why snakes do it,
save for to hide vulnerable parts from potential predators.
Presented
here are examples of balling behavior seen in Australian elapid snakes.
A
SHIELD FROM A PREDATOR
In
1996, I photographed an adult "whip snake" of the species Suta
dwyeri from north of Windsor, NSW.
Upon
removing the snake from a plastic container, it coiled itself into a tight ball
in which it hid it's head.
This
response is common to snakes from this and similar genera and I have observed
it numerous times.
The
only known reason for this behavior is to shield the most vulnerable parts (the
head) from predators.
I
have also observed balling in the same situations in Antaresia stimsoni
(see photo in Hoser 1989) and young Diamond Pythons (Morelia spilota).
TO
ESCAPE FROM A PREDATOR, BY ROLLING OR AVOIDING DETECTION DUE TO THE SHAPE OF
THE BALL
In
August 2003, I was raking leaves under an acacia tree at Tiddy Widdy Beach,
Ardrossan, South Australia.
As
I raked leaves a balled up Death Adder (Acanthophis antarcticus) rolled
past my body.
At
first I didn't notice the snake as it rolled like an inanimate object (the
snake was tough and rigid) and it was of similar colour and consistency to the
other leaves and vegetation being raked.
In hindsight I was lucky that the snake was actually detected by myself.
At
the time the air temperature was cold (10°C) and it is true that the snake may have also been
tightly coiled to retain heat.
Noting
this possibility, the snake was then gently poked and rolled around with a
stick and it became evident that the snake chose not to respond to the
poking. In other words it appeared to
be deliberately playing dead or similar.
Once
forcibly grabbed, the snake immediately outstretched itself and tried to squirm
free and it's relatively rapid movement implied that the prior rigidity was not
a result of it being cold at the time (as in the snake was not being held stiff
and immobilized due to severe cold).
In
terms of balling being a defence, it is easy to see how it'd favor the snake.
If
it's area was being raked by a large predatory bird (e.g. Emu) in search of
small animals for food, it'd be to the snake's advantage to pretend to be a
ball or lump of material, rather than to present as a small snake or
"worm" which would be welcomed by the bird as food.
Hence
the snake could literally roll-away as it is raked and wait until the bird or
other digging animal has left the area before it unballs itself to move away.
This
theory works in well with the underlying view that snakes prefer to be not seen
rather than having to snap, bluff or bite other animals in order to avoid attack
or predation.
To retain heat in extremely cold or rapidly cooling
conditions
This
reason to ball has only been seen by me in artificial situations such as when a
snake is placed in a container in the fridge or freezer.
The
snake balls itself in order to reduce the heat loss that would otherwise be
more rapid if the snake were to remain outstretched.
This
is noticed when placing active snakes in a plastic container and then into a
fridge or freezer.
When
placing snakes of several taxa in a fridge, including Tiger Snakes (Notechis
scutatus), Eastern Brown Snakes (Pseudonaja textilis) and
Red-bellied Black Snakes (Pseudechis porphyriacus), these snakes have
tended to ball up in order to avoid the cooling.
This
they do as soon as the snakes realise that they cannot escape the container and
when the cool air affects them.
On
relatively unusual occasions when snakes do not ball, they will move about
their container in order to find an escape route, which is the only other
defence they have against extreme cold.
While
cooling in the wild state may not be as fast as seen by placing a snake in a
fridge or freezer, there is no doubt that similar environmental temperatures
may occur and that snakes would sometimes either get caught in them, or seek to
avoid their most severe consequences.
Hence
the adaptation of balling to retain heat appears to be one that would also be
seen in wild snakes. This also explains
why in cooler weather, snakes found under cover tend to be tightly coiled and
may sometimes aggregate.
REFERENCE
Hoser, R. T. 1989. Australian
Reptiles and Frogs. Pierson and Co., Sydney, NSW, Australia:238 pp.