Jeroen Speybroeck wrote:But... as long as no one has seen this in the field (at least such a swolen head), how can you know this is natural behaviour? I'm sure, Mario, you are aware of that, but it needs mentioning nevertheless. Impossible to assess its significance, but interesting in terms of viper's venom metabolisation.
For sure, these bites (escalated combat) may be terrarium artifacts.
The same opinion has Thomas Kölpin: "No occurrence of escalated combats of snakes in nature has been described until now indicating that escalated combats may be an artifact of captivity."
Full paper
here.
This text I´ve found on the net - unfortunately no link saved: "Most males battling for a female will not bite each other and instead wrestle to try to force their rival’s head to the ground. The battle is more like a dance; combatants may “stand” erect parallel to each other, or twine around each other like a rope. A few snakes do actually bite each other. Sometimes a female initiates the first stage of combat and wrestles with the male. She will reject the suitor if he does not respond forcefully."
On the other hand: The chance to see such an escalated combat - or just the swolen head after a bite - is something like zero.
From my observation, the swelling leasts from 3 to 12 hours and the "victim" is hiding during this time.
So it might be more easy to find a two-headed albino Vipera ammodytes, with a straight orange dorsal line
Mario