Now you can't unsee it. You're welcome.
It looks like a French tickler, but much more like something used by Torquemada on stubborn Jews and Muslims. Those spikes at the tip are actually nasty, painful spikes and when the particular beetle that this particular penis belongs to, the seed beetle or bean weevil (Callosobruchus maculatus), inserts it into the female, it's... not pleasant. It tears up the vagina and can cause terrible internal injuries that leave visible scars. Ugh...
But the big question is why did this nightmarishly horrific torture device evolve in the first place? Well, they may simply cause so much damage that the female will smack any other male beetle across their mandibles if they try to have sloppy seconds, ensuring her first mate's genes passage into the next generation. But they may also be a result of sperm competitions, where males play the odds by fertilizing many eggs. They ejaculate as much as possible during sex while the spines serve some other purpose in (maybe literally) cockblocking sperm from other males. Any internal damage the female suffers is just a side-effect -- a very, very painful side-effect, but a side-effect nonetheless.
A study carried out by Cosima Hotzy and Goran Arnqvist of Uppsala University recently concluded that may implicate just that, as Ed Yong of Not Exactly Rocket Science explains:
The duo studied beetles taken from 13 countries across the tropics, from Brazil to the USA, and from Nigeria to Oman. The genitals of these different populations are very varied and to study them under a microscope, Hotzy and Arnqvist first had to fluff their subjects. They anaesthetised the males with carbon dioxide, and erected their penises with an "artificial inflater" - a microscopic plastic tip connected to a pump.
Beetle penis pump? Who knew?
Under a microscope, they measured the length of the longest spines and the size of the entire spine-bearing area.
They studied female beetles too, and all from a single population. Each one was allowed to mate once with a single male. A week later, Hotzy and Arnqvist dissected their sexual tracts to see how much scarring they had, using the distinctive black pigments on the scars to spot them. As you might expect, the males with the spiniest genitals inflicted the most amount of scarring on the females, in a way that was independent of the partners' overall body size.
To measures the effects of these spines on the males' reproductive success, the duo first mated virgin females with males from a single Nigerian population, who had all been sterilised by radiation. Two days later, the females were then paired with a second male, taken from one of the 13 worldwide populations. One week later, they counted all the eggs she laid. Every one of these must have been fathered by the second male, so their number represents his ability to successfully oust the sterile sperm of the first partner.
Again, the males with the longest penile spines were more likely to be the victors of the sperm competition and again, this link had nothing to do with either the male's body size or his general health. The degree of scarring in the females was also linked to the male's success at sperm competition, but to a much lesser extent and certainly not when the length of the spines was taken into account. It is the spines, rather than the damage they inflict, that is the key to the male's success.
What the spines actually do is a mystery, but the correlation between sharp, nasty, pointy penis spines and reproductive success exists. It's not like the females are without defenses against the mace shoved into her though:
The female seed beetle, for example, has a huge amount of connective tissue lining her sexual tracts so that the damage inflicted by the males doesn't affect her too badly. She also takes a more direct approach to protecting herself - when she's had enough, she simply kicks the male until he lets go.
Unfortunately this isn't the most painful example of bug sex, and apparently when it comes to painful sex, nobody beats the bugs. Yong describes the dung fly, that has armor on its penis, and the familiar laboratory insect, the Drosphillia fruit fly, that actually injects lethal toxins along with its sperm to kill other sperm from other males. They also drastically shorten the life of the female, and they can literally fuck themselves to death by poisoning. But they don't hold candles to the infamous bed bug:
And possibly the most cringeworthy sexual technique of all belongs to the male bed bug, whose penis is like a hypodermic needle. He stabs it through the female's back and injects his semen straight into her abdominal cavity. It's a method that's been appropriately named "traumatic insemination".
Do not want... Yet another reason not to have these crawling around your bed.
National Geographic also covered this and has some fun pictures, including the shot I used at the beginning. And some hardcore beetle porn. You're welcome again :3