1. Elephant ᴘᴇɴɪses are prehensile.
Speaking of elephants: The elephant ᴘᴇɴɪs is so huge that ᴍᴀʟᴇs can rest on it like it’s a leg. When ᴇʀᴇᴄᴛ, it can weigh in at 66 pounds and can be more than 3 feet long. It’s also prehensile, which means that an elephant can move it around and even use it to sᴄʀᴀᴛᴄʜ ʜᴀʀᴅ to reach places. As we mentioned, feᴍᴀʟᴇ elephants have long reproductive tracts—nearly 10 feet from start to finish—and the ᴠᴀɢɪɴᴀ doesn’t ʙᴇɢin until about 4.27 feet in, so the elephant ᴘᴇɴɪs doesn’t enter the ᴠᴀɢɪɴᴀ.
2. One Australian marsupial has s.ᴇ x until it ᴅɪᴇs.
The Antechinus is a mouse-like marsupial that ᴇᴀᴛs insects, nests in trees, and has so much s.ᴇ x that it literally ᴅɪᴇs. By the time they ʜɪᴛ 11 months old, ᴍᴀʟᴇs of this species have produced all the sᴘᴇʀᴍ they’ll crᴇᴀᴛe in their short lifetimes; for the next couple of weeks, they’ll go at it for up to 14 hours at a time with one feᴍᴀʟᴇ before moving on to another, over and over again, until their boᴅɪᴇs ʙʀᴇᴀᴋ ᴅᴏᴡɴ. The ᴍᴀʟᴇ’s fur wɪʟʟ fall out; he’ll ʙʟᴇᴇᴅ internally; he’ll get gangrene and any number of other ɪɴfᴇᴄᴛions, ultiᴍᴀᴛᴇly ᴅʏɪɴɢ before he reaches one year. But he’s ᴄʜᴀsɪɴɢ tail up until the end: As Diana Fisher from the University of Queensland told National Geographic, “By the end of the ᴍᴀᴛɪɴɢ season, physically disintegrating ᴍᴀʟᴇs may run around frantically searching for last ᴍᴀᴛɪɴɢ opportunities. By that time, feᴍᴀʟᴇs are, not surprisingly, avoiding them.” The laᴅɪᴇs are a little luckier, at least if they’re of larger Antechinus species: Between 30 and 50 percent of them wɪʟʟ live to produce two litters.
3. Mouse sᴘᴇʀᴍ is bigger than elephant sᴘᴇʀᴍ.
Sorry, dudes: The size and shape of a ᴍᴀʟᴇ animal’s sᴘᴇʀᴍ is more related to the biology and ᴍᴀᴛɪɴɢ practices of the feᴍᴀʟᴇ—which is why mouse sᴘᴇʀᴍ is longer than the sᴘᴇʀᴍ of the biggest land animal on Earth, the elephant.
Two major factors in sᴘᴇʀᴍ size include the literal length and size of the feᴍᴀʟᴇ reproductive tract and how many ᴍᴀᴛɪɴɢ partners the feᴍᴀʟᴇs have. Mice produce big sᴘᴇʀᴍ beᴄᴀᴜsᴇ, in most species, feᴍᴀʟᴇs have a lot of partners. The grouping of sᴘᴇʀᴍ can help to increase its competitiveness in promiscuous animals. Accordingly, the deer mouse has sᴘᴇʀᴍ equipped with small hooks that helps them clump together in groups of up to 35 sᴘᴇʀᴍ to fɪɢʜᴛ their way to the egg. Grouping sᴘᴇʀᴍ allows the cluster to swim in a straighter line to the egg; the ideal number is seven. Too many sᴘᴇʀᴍatozoa wɪʟʟ eventually start working ᴀɢᴀɪɴsᴛ each other. Meanwhile, feᴍᴀʟᴇ elephants have a very long reproductive tract (more on that below), so ᴍᴀʟᴇ elephants have evolved to produce more but smaller sᴘᴇʀᴍ to ᴄᴏᴍʙat the ʀɪsᴋ of dilution. To follow the reproductive strategy of mice sᴘᴇʀᴍ, elephant sᴘᴇʀᴍ would need to be scaled up enormously to make a difference.
4. Monogamy makes for small gorɪʟʟa ᴘᴇɴɪses.
You’d never know it by looking at them, but ᴍᴀʟᴇ gorɪʟʟas have surprisingly tiny ᴘᴇɴɪses: They measure just 1.5 inches in length when ᴇʀᴇᴄᴛ. How can an animal that weighs up to 485 pounds be so humbly endᴏᴡᴇᴅ? It’s beᴄᴀᴜsᴇ priᴍᴀᴛᴇ ᴍᴀᴛɪɴɢ practices are a huge factor in the evolution of the ᴍᴀʟᴇs’ ɢᴇɴɪᴛᴀʟia. When ᴍᴀʟᴇs have to ᴄᴏᴍᴘᴇᴛᴇ among other ᴍᴀʟᴇs—as the s.ᴇ xually promiscuous bonobos do—the species’ ᴘᴇɴɪs size is bigger. In gorɪʟʟa society, ᴍᴀʟᴇ silverbacks ᴍᴀᴛᴇ with many feᴍᴀʟᴇs who are all monogamous to him. No reproductive competition equals a tiny ᴘᴇɴɪs.
5. Nᴀᴋᴇᴅ mole rats have ᴅᴇfᴏʀᴍed sᴘᴇʀᴍ.
The wrinkly, nearly ʙʟɪɴᴅ ɴᴀᴋᴇᴅ mole rat is a successful ʙʀᴇᴇᴅer despite how inept its sᴘᴇʀᴍ is at being sᴘᴇʀᴍ. Small, ᴍᴀʟfᴏʀᴍᴇᴅ—many have multiple heads or are shaped oddly—and deficient in the mitochonᴅʀia that most mammal sᴘᴇʀᴍ rely on for energy, just 15 percent, max, of the ɴᴀᴋᴇᴅ mole rat’s sᴘᴇʀᴍ can swim; only 1 percent can move quickly. The animals don’t produce that much sᴘᴇʀᴍ, either. These ᴡᴇɪʀᴅ quirks may be due to the fact that the queen ᴍᴀᴛᴇs with only one ᴍᴀʟᴇ, so sᴘᴇᴇdy, normal sᴘᴇʀᴍ isn’t necessary to guarantee the continuation of the species.
6. Bee sᴘᴇʀᴍ wages war.
Mᴀʟᴇ honey bee ᴅʀones are infamous for ᴇxᴛʀᴇᴍᴇ ʙʀᴇᴇᴅing. These bees have an internal ᴘᴇɴɪs—a.k.a. an endophallus—which, during ᴄᴏᴘᴜʟᴀᴛɪᴏɴ, is turned inside out and inserted into the queen. As he ᴇjᴀᴄᴜʟᴀᴛᴇs, the ᴅʀone falls back, ʙʀᴇᴀᴋing off his ɢᴇɴɪᴛᴀʟia inside the queen and ᴅʏɪɴɢ in the process. In theory, this sacrifice would lock his sᴘᴇʀᴍ inside and block out any competitors’, ensuring that his genes were passed on. But ᴜɴfᴏʀᴛᴜɴᴀᴛᴇly that’s not what happens. As Social Insects: An Evolutionary Approach to Castes and Rᴇᴘʀᴏᴅᴜᴄᴛɪᴏɴ explains, “The next [ᴅʀone] to ᴄᴏᴘᴜʟᴀᴛe removes the ᴍᴀᴛɪɴɢ sign [the endophallus plug] of his predecessor with the hairy ventral part of his own endophallus before he is able to insert its bulb and ᴇjᴀᴄᴜʟᴀᴛᴇ the sᴇᴍᴇɴ.” The next ᴅʀone wɪʟʟ do the same, and on and on. Of the 90 mɪʟʟion sᴘᴇʀᴍ that end up in the queen’s oviducts, only 7 mɪʟʟion make it to a pouch called the sᴘᴇʀᴍatheca. She uses that sᴘᴇʀᴍ over the course of her life to fᴇʀᴛɪʟɪᴢe eggs.
That is just the start of the story when it comes to bee s.ᴇ x. In species where multiple ᴍᴀʟᴇs ᴍᴀᴛᴇ with the queen, the sᴘᴇʀᴍ wage ᴡᴀʀ with each other inside of her. (This happens in some species of ants, too.) When ᴍᴀʟᴇs get a little too ᴠɪᴏʟᴇɴᴛ, queens from some species wɪʟʟ give off chemicals to calm everyone ᴅᴏᴡɴ.
7. Banana slugs ᴍᴀᴛᴇ using ᴘᴇɴɪses on their heads.
Banana slugs are huge, they ᴇᴀᴛ your garden, and they leave a slimy trail as they squirm across the ground. Their method of ʀᴇᴘʀᴏᴅᴜᴄᴛɪᴏɴ is no more pleasant than their appearance: The scientific name for one species of banana slug is Ariolimax dolichophallus, the second part of which means “long ᴘᴇɴɪs,” and it’s apt. The inᴠᴇʀᴛᴇʙʀᴀᴛᴇs’ ᴘᴇɴɪses can be 6 to 8 inches long—the entire length of the slug’s body. When it’s time to get ᴅᴏᴡɴ, the ᴘᴇɴɪses grow out of pores in the head. It isn’t ᴜɴᴜsᴜᴀʟ for the ᴘᴇɴɪs of one slug to get sᴛᴜᴄᴋ inside the other during ᴄᴏᴘᴜʟᴀᴛɪᴏɴ; to solve this uncomfortable situation, the slug on the receiving end wɪʟʟ ᴇᴀᴛ the ᴘᴇɴɪs that’s sᴛᴜᴄᴋ inside it.
8. Feᴍᴀʟᴇ neotrogla penetrate the ᴍᴀʟᴇs.
Neotrogla, a fly-like insect that lives in a cave in Brazil, is the first-ever species found that has “opposite” ɢᴇɴɪᴛᴀʟia. The feᴍᴀʟᴇs are equipped with spiny, ᴘᴇɴɪs-like ɢᴇɴɪᴛᴀʟia called gynosomes, which they use to penetrate the ᴍᴀʟᴇ; then, the insects get it on for up to 70 hours as the ᴍᴀʟᴇ transfers sᴘᴇʀᴍ and nutrients to the feᴍᴀʟᴇ. If the two are separated during ᴄᴏᴘᴜʟᴀᴛɪᴏɴ, the ᴍᴀʟᴇ’s insides wɪʟʟ be ripped out while the feᴍᴀʟᴇ ʀᴇᴍᴀɪɴs intact.