If you looked at the penis of a Drosophila fly under a microscope (for reasons best known only to yourself), you’d see an array of wince-inducing hooks and spines. These spines are present in all Drosophila and they’re so varied that a trained biologist could use them to identify the species of the owner.
What’s the purpose of these spines? Are they intended to actually wound the female during mating? Do they help the male fly to scrape out the sperm of his rivals? Do they actually pierce the walls of the female’s genital tract, allowing the male to bypass any barriers to his sperm, as other insects do? All of these explanations have been put forward, and it seems that all of them are wrong.
The spines are nothing more than biological Velcro. During sex, they help the male fly to clasp onto his mate from the inside so he can’t be easily dislodged. We know this thanks to Michal Polak and Arash Rashed, who shaved male flies with a laser to see if their sexual performance would be affected.
Normally, the duck keeps its penis inside-out within a sac in its body. When the time for mating arrives, the penis explodes outwards to a fully-erect 20cm, around a quarter of the animal’s total body length. The whole process takes just a third of a second and Brennan captures it all on high-speed camera. This isn’t just bizarre voyeurism. Duck penises are a wonderful example of the strange things that happen when sexual conflict shapes the evolution of animal bodies.
Childhood… violated… Innocence… lost… SCIENCE!Many ducks form bonds between males and females that last for a whole mating season. But rival males often violently force themselves onto females. To gain the edge in these conflicts, drakes have evolved large corkscrew phalluses, lined with ridges and backward-pointing spines, which allow them to deposit their sperm further into a female than their rivals. These extreme penises are even more unusual when you consider that 97% of bird species lack any penises whatsoever.
But female ducks have developed countermeasures. Their vaginas are equally long and twisting, lined with dead-end pockets and spirals that curve in the opposite direction. They are organic chastity belts, evolved to limit the effectiveness of the males’ lengthy genitals. Two years ago, Brennan showed that duck species whose males have the longest penises tend to have females with the most elaborate vaginas. Now, she has found further evidence that these complex genitals are the result of a long-lasting war of the sexes.
This is a bull elephant firmly establishing why it is he, and not the lion, who is king of beasts. The elephant’s penis is not only massive but prehensile. As we watched in baffled amusement (and the faintest tinge of inadequacy), he used his penis to prop himself up (as in the photo), swat flies from his side and scratch himself on his stomach. David Attenborough never showed us that…
There’s good reason for elephants to have prehensile penises. It’s hard enough for a six-tonne animal to get into the right position for sex, let alone having to do the rhythmic thrusting that’s required. So he let’s his penis do all the work for him.
You’ll also note the dark stain behind his eye – that’s a leak from his temporal gland. It means that this male was entering musth, the period when their testosterone shoots through the roof and they get incredibly horny and aggressive. We tried to drive round this male and he basically charged us. Tramply doom was averted by our driver who slammed his palm against the car door as hard as he could. The elephant stopped and huffed and puffed. We did our best to not soil ourselves.
This picture gives you an idea of how close he was. After a seemingly infinite standstill, he moved aside, extended his enormous penis and had a wee. It’s amazing how terror can convert into comedy so quickly…
The courtship rituals of the spider Harpactea sadistica start innocently enough, with a dance and a hug. The male spider taps the female gently with his front legs and embraces her. But from that point onwards, things for the female go rapidly downhill. The male bites her and she becomes passive, allowing him to manoeuvre her into position. Like all spiders, his genitals are found next to his head, on a pair of appendages called the pedipalps. But unusually, his penis ends in a needle-sharp tip called an embolus.
The embolus sits at the end of a loop called the conductor. The male hooks one of these loops around the opposite embolus to steady it. Then, by rotating the anchored needle, he drives the point straight through the female’s underside and ejaculates directly into her body cavity. On average, he does this six times, moving slowly downwards and alternating between his two penises. The entire cringeworthy sequence lasts about 15 minutes and throughout it, the male spider never penetrates the female’s actual genital opening.
The species was discovered in Israel last year by Milan Rezac from the Crop Rsearch Institute in the Czech Republic. He named it well. H.sadistica practices a style of sex that’s understandably known as “traumatic insemination“. It’s disturbingly common among insects and other invertebrates, and is most famously practiced by bedbugs. But this is the first time that the behaviour’s been seen among the chelicerates – the group of animals that includes spiders, scorpions and mites.
You can see it happening in the videos below. In the first, the male spider bites and incapacitates the female. In the second, he hooks the conductor of one pedipalp around the embolus of another and, with rotating motions, drives it into the female. These videos aren’t pretty – you’ve been warned.