When you think of large genitals a barnacle is probably the last thing you think of. In fact, in proportion to body size, barnacles have the largest penises in the animal kingdom, reaching up to 10 times the length of their body.
In 2008, J. Matthew Hoch conducted a study that explored the wonderful world of barnacle sex. In an article that was published in the Journal of Experimental Marine Biology and Ecology, Hoch found that there was more to just the staggering size of a barnacle penis.
It seems that over time barnacles have evolved ways to change the shape of their penis to maximise reproductive success.
Close aggregation of barnacles. [Image from shutterstock]
Barnacles are sessile creatures, so living in un-crowded areas means it’s not always easy to mate. To overcome this hurdle, barnacles are able to elongate their penis so they can reach a mate and inseminate them from further distances.
However, when it comes to rough tides and wave exposure, the barnacle is able to increase the diameter of the penis to strengthen it and decrease the chances of ‘falling out’ before insemination.
Unsurprisingly, having such a large member comes at a cost. The placement of the penis, located so close to the feeding apparatus, may reduce feeding efficiency. “As penises grow larger, interference with feeding is expected to increase” states Hoch.