Balling as a defence mechanism for snakes
488 Park Road
Park Orchards, Victoria, 3114, Australia.
First published in hard copy in Boydii (Journal of the Herpetological Society of Queensland), Spring 2005.
"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.
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.
Hoser, R. T. 1989. Australian Reptiles and Frogs. Pierson and Co., Sydney, NSW, Australia:238 pp.