Hi Chantilly
Assuming that they have been sexed correctly which is much easier when they are adults many get mis sexed with they are younger if your unsure there are plenty of articles on line showing the difference.
So assuming it's a male and female its normal male behaviour he wants to mate, the male is naturally aggressive towards the female during mating the male bites the back of the females neck.
They should be separated as the male will constantly harass the female otherwise its normal.
2 females will happily live together but 2 males will fight.
Hope that helps





