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I remember when I was a child, after I realized the role and function of human reproductive organs, that I had a realization that all other non-human animals have basically the same idea of sex. It is composed mostly of males with some fleshy appendage, forcing themselves upon females with organs designed to receive said appendage. This may seem obvious, but today I had another realization that I had not given evolutionary variability the credit it deserves when it comes to copulation.

In reference to our recent Valentine’s Day, below are examples of the diversity of sex in the animal kingdom: a selective suicide and absorption of the male angler-fish, an aide to some mammals that puts Viagra to shame (an actual bone (I mean exactly what you think I mean)), and beyond this you can find a few more interesting facts about animal sexuality.

Angling for a Mate

This bizarre-looking fish is a female anglerfish (Linophryne brevibarbata) with a male attached to her. Upon encounter, a rare event in the sparsely populated depths of the sea, the male bites into the female’s skin and doesn’t let go. Their tissues fuse, their blood vessels join and the male slowly atrophies (his body degenerates as if it was in a coma), first losing his digestive organs, then his brain, heart and eyes until he is nothing more than a pair of gonads (testes).

In this image, the small pipe-shaped structures clinging to the female’s bulbous underside is the atrophied body of the male. The female can carry several males on her body at once, ensuring a constant supply of fresh sperm for when she is ready to spawn. Animal sperm banks ask a high price.

Penis Bones


This photo shows walrus, Great Dane and raccoon penis bones, or bacula. The baculum, which aids rigidity during mating, is found in the penis of many mammals. The largest baculum belongs to the walrus and can measure a whopping 75 centimetres (2 and a half feet!). Humans don’t have a baculum, instead, men have a vascular penis which fills with blood to achieve an erection (and obviously are jealous).

Like most science, there’s still a lot of debate about the function of the bacula. Is it simply to prolong sexual intercourse? Some scientists speculate that, in some species, it’s actually there to do damage to the female genitalia so as to ensure she won’t mate again in a hurry.

This is known as sperm competition, and some animals take the tactic to extreme lengths: the banana slug bites off its own penis to leave it in the female, preventing others from depositing more DNA.

Doing it Like they Do on the Discovery Channel

Natural it may be, but animal reproduction can be a mighty strange business.

  • Barnacles, for instance, have a penis 30 times their body length.
  • Male snakes have a forked organ, allowing them to dodge the female’s tail and penetrate from either direction.
  • Hedgehogs plug their partner’s vagina with excess sperm to stop anyone else’s getting a look in.
  • Blue fairy wrens have testicles 25% their body weight.
  • The female hyena picks and dumps her male as she sees fit, and has even evolved genitalia that look like a male’s.


The difference is size between the male and female Black Widow spider

One of the most common animals that comes to mind in relation to their sexuality is the spider. The common practice for the female spider to eat the male after sex is what really triggers our “that’s weird” reflex because it seems completely opposite to the ideals of human love and personal connections that are associated with sex. But we have to realize that our feelings about sexuality are just one of the many offshoots from our evolution, and that many other viable sexual practices are just as evolved as ours. Because, when it comes down to it, romance aside, the purpose of our sex drive and passion is to pass on our genetic material. Spiders, as with the rest of the animal kingdom, do not disappoint when exhibiting the variability of nature.

Adult male spiders don’t have a penis at all. Instead, they produce a sperm web, deposit their sperm on to the web, and then draw it up into the palps (a pair of small, claw-like structures at the front of their bodies). They then slot their palps into the female like a lock and key, and have evolved a lot of strategies to do it so.

Compared with your average male spider, humans have it easy. Essentially, the male has to make sure the female is in the mood to mate, he has to show her he’s of the same species, and he has to demonstrate he’s not food. If he gets any of those three things wrong, he may well get eaten, because in most cases the female is bigger than the male.


  • A tarantula will stroke the female’s legs to ensure she is receptive.
  • A common garden spider will spin a web and then pluck its threads in a certain way to inform a female he’s there; in another species, the female will produce a perfumed “drag line” (a single line of thread impregnated with pheromones) to provoke a male’s courtship dance.
  • Male crab spiders spin loops of silk around a female to calm her down and get her in the mood.

Some spiders are into gift-giving and, generally speaking, the bigger the gift, the longer the copulation lasts. Others are into vaginal plugs (the tip of the palp breaks off), or will fight off rival suitors after the act. Male jumping spiders semaphore with their palps and body parts, prompting a gender-specific female dance that sends the male into a frenzy of sexual “anticipation”.

For many male spiders the risk, of course, is that copulation necessitates placing his juicy abdomen in front of his partner’s jaws (although some have evolved mechanisms to prevent those jaws from closing). But in evolutionary terms that makes sense because males have a far shorter lifespan than females anyway, and if they get eaten, that means that he’s been in the right position for longer and the female’s well-fed. In short, his genes will get passed on. He’s not been wasted.

Weirdly Similar

Other animals certainly exhibit similar aspects of our human sexuality. They entice mates, they give gifts, they sleep around, and they go out to eat (sometimes each other). It is fascinating to view these similarities along with the seemingly bizarre differences between us and them. But, in the end, our infatuations are the result of a finely tuned instinct to pass on our genes, and throughout the animal kingdom, we witness the other evolutionary avenues to this end.