There’s a famous picture that has probably been burned into the retinas of anyone who spends a lot of time on the internet. It’s a squirrel, standing up, with a surprisingly huge pair of testicles dangling beneath him. That’s a Cape ground squirrel and the image isn’t a fake. Males have a scrotum that’s 20% of their body length (excluding the tail) and their penis is more than twice as long.
These mighty genitals suggest that sex, and sperm in particular, is a serious business for Cape ground squirrels. To get the best odds of fathering the next generation, they need to ensure that it’s their sperm that fertilises the female’s eggs and not those of rivals. So they make a lot of it; hence, the oversized testicles.
With sperm being so important, it’s odd that some Cape ground squirrels regularly waste theirs. Yet that’s exactly what Jane Waterman saw while studying wild squirrels in Namibia. Some of them would masturbate, apparently squandering their precious sperm. What does squirrel masturbation look like? Apparently, it’s rather acrobatic. I’ll let Waterman describe it herself:
“An oral masturbation was recorded when a male sat with head lowered and an erect penis in his mouth, being stimulated with both mouth (fellatio) and forepaws (masturbation), while the lower torso moved forward and backwards in thrusting motions, finally culminating in an apparent ejaculation, after which the male appeared to consume the ejaculate.”
Sex might be fun but it’s not without risks. As your partner exposes themselves to you, they also expose you to whatever bacteria, viruses or parasites they might be carrying. But some animals have a way around that. Ekaterina Litvinova has found that when male mice get a whiff of female odours, their immune systems prepare their airways for attack, increasing their resistance to flu viruses.
Litvinova worked with a group of mice that were exposed to bedding that had previously been soiled by females in the sexually receptive parts of their cycle. She compared them to a second more monastic group that were isolated from female contact.
Male mice use smells to track down females who are ready to mate. They’ll follow markings of faeces and urine and when they actually find the female, they’ll continue sniffing her nose and genitals. Each of these nasal encounters could be a source of infection. She then pitted both groups against a flu virus. Influenza doesn’t affect wild populations of house mice, so the virus in this case is acting as more of an indicator of the animals’ defences, rather than a representative of a real threat.
Both groups of mice lost a bit of weight, but at certain doses of virus, those that had been exposed to female aromas kept more of their grams on. They also fared better in the long run – just 20% of them died, compared to 46% of those that had only smelled male odours.