Male and female hamsters look similar at first glance. They don't have obvious differences in colour, as seen in many pet birds or size, as seen in other rodents such as rats. Naturally, it is useful to know the gender when naming a hamster, and it may influence behaviour and disease risk. In the case of dwarf hamsters, which should be kept in pairs or small groups, it is crucial to know the sex. The situation of buying two girl hamsters that turn out to be a boy and a girl usually results in baby hamsters, which aren't particularly easy to find good homes for.
The external genitalia of hamsters is unobtrusive and quite difficult to see. To sex a hamster, pick it up and turn it upside down. Female hamsters have two tiny holes very close together near the tail. Males also have two little holes -- the penis retracts --- but the holes are further apart, nearly 1/2 inch in Syrian hamsters. They also have testicles nearer the body, which they can retract. Male dwarf hamsters have scent glands on their bellies, roughly where a naval would be in humans. Female hamsters have nipples running on either side of the belly, but these are very difficult to see, especially on dwarf hamsters or longhair Syrian hamsters.
Buying Male or Female Hamsters
It is recommended you buy hamsters from a breeder or get them from an animal sanctuary, and these places will know the gender. If you plan to take a hamster from anywhere else, such as a friend or neighbour, you'll need to sex it. Pet shop staff may not know how to sex hamsters so it is always advisable to check yourself, even if the staff insist a certain tank only contains male or female hamsters. With Syrian hamsters, you can wait until the hamster matures and the process is easier if you are unsure. There is no risk of a solitary hamster breeding. With dwarf hamsters, you may need help. A local rodent club could provide assistance. It may also be worth taking all the hamsters to the vet for an initial check-up and sexing.
While the effects of gender on disease risk are well known in well-studied animals such as rats and larger pets such as cats, dogs and rabbits, much less is known about hamsters. Female hamsters appear more prone to cancers, mainly cancers of the uterus.
Anecdotal evidence, which is not proof, suggests female hamsters spend more time hoarding food and making nests and make more determined efforts to escape. Scientific studies have shown there are some clear differences in the social behaviour of male and female hamsters. For example, male hamsters remain submissive if they lose a fight with another male for much longer than females, who may be submissive only briefly or not at all.