Penises come in a remarkable range of shapes and sizes, says Stuart Blackman, as he investigates which animal has the biggest
Considering their rather straightforward function in life (to deliver a male’s sperm into a female’s body to fertilise her eggs), penises come in a remarkable range of shapes and sizes.
Long ones, short ones, thick, thin, straight, bent, branching and curly ones. Some have a bone inside them, others are inflatable, and many are adorned with all manner of bristles, hooks, folds, flaps and flanges.
Which animal has the biggest penis?
Size-wise, it’s probably no great surprise that the biggest penis of all belongs to the largest animal ever to have existed. A blue whale’s penis extends to up to three metres in length. That’s considerably bigger than an elephant’s (one to two metres), which is probably the record-holder among land animals.
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But there’s also relative size to consider. A blue whale’s penis is about a tenth the length of the animal itself.
The duck corkscrew penis
But a male Argentine lake duck’s is about as long as he is. Proportionately, it’s the biggest penis among all vertebrates (and it also happens to be shaped like a corkscrew).
When not in use, it’s tucked away inside the body, but is erected explosively under internal pressure, like an inverted finger popping out of a rubber glove.
A longer penis can deliver sperm further inside the female, and hence closer to the eggs, which may be a great advantage to the males of species (Argentine lake ducks included) in which females mate with multiple males. The many spiny projections covering the duck’s penis, which are thought to be involved in removing the sperm deposited previously by other males, are also the result of competition between males.
Size matters very much to barnacles, too, to the point that even a well-endowed lake duck cannot compete. Anchored as they are to one spot for the entirety of their adult lives, these peculiar crustaceans (they are basically shrimp-like animals that glue themselves on their backs to rocks and wave their legs around to catch food) are unable to go off in search of a mate. Instead, they rely on an extraordinarily long penis to do the searching for them.
Doubling the length of the penis quadruples the area – and hence the number of mates – that can be reached. And barnacles have pushed theirs to the point that it becomes a liability. At up to eight times their body length, this flexible appendage is at risk of being snapped off by the currents. Indeed, barnacles living in choppy waters grow shorter, stouter members compared to those in more sheltered spots. And once the mating season is over, the enormous organ is reabsorbed and regenerated the following year.