Someone I know has Puff adders and Horned adder (Bitis caudalis) in the same cage. Despite my warning he left them together. A few nights ago he checked on them during the night and found this:
He thought the puff adder was mating with the horned adder because he knew for a fact the puff adder was a male. The puff adder is also small and probably a yearling. It is quite obvious that the Horned adder was mating with the puff adder and with them both being male nothing can come of this.
This was recorded at the Transvaal museum as well and the male puff adder was very indignant and wanted to kill the male horned adder.
It is strange that this should happen twice and in both cases there was not a female horned adder in the vicinity. Captivity does strange things to people and animals.