Worm Sex


Words || Freya Wadlow

Content warning: may contain the literal word ‘moist’.

Not to kinkshame Mother Nature, but reproduction in the animal kingdom is WILD. From the corkscrew-shaped penis of male ducks to the honey bee’s exploding genitals; the dynamic evolution of life on earth has seen the rise of copulation that is both creative and terrifying. However, none take on this challenge of freakily producing offspring more vivaciously than the humble worm.

Worms are a complex grouping of many distantly related animals that typically have a long cylindrical body without limbs and are found in marine and terrestrial environments. They vary in size: from microscopic, to over 50 metres (Lineus longissimus). Worms reproduce asexually and sexually, and are often hermaphroditic (presenting both male and female associated sex characteristics). Asexual reproduction largely takes the form of fragmentation and budding, where a genetically identical clone is regenerated from a part of the body that has been split off. Scientists are currently studying planarian (a type of flatworm) regeneration with the aim of uncovering how to regenerate human tissues and cells, such as insulin-producing or nerve cells!


Flatworms are part of the phylum Platyhelminthes, which includes parasitic tapeworms and flukes. Being hermaphroditic, flatworms face the difficult question of which parental role to undertake. And let’s be honest – being a mum is tough. Propagating the species is a much larger investment for females than males in most species. Whilst males have a large quantity of gametes in store to spread their genes to one or multiple partners, females must create and incubate eggs and, depending on the species, spend a significantly longer time caring for offspring. Flatworms deal with this sensitive and delicate issue by trying to stab the other with their needle-like penis spicule, with the first to inseminate winning. Known as traumatic insemination, or ‘penis fencing’, this duel of the fates can last up to one hour, with flatworms often stabbed multiple times from the double-headed penis of its opponent. The ‘loser’ then immediately begins to search for food to make up the resources required for their new maternal position.


Some flatworms decide to skip the whole process altogether and in an act of horrifying self love, literally have sex with their own head. The transparent flatworm, Macrostomum hystrix has female organs towards their cephalic (head) region, and male sperm-producing organs towards the tail. In a study from the University of Basel, researchers found that isolated flatworms, after a period of time, would end up with more sperm in their head, compared to those kept in groups. This placement suggests the worms had used their penis to puncture their own head and inject sperm. While some hermaphrodites are known to be able to self-fertilize, this convoluted mechanism is thought to have occurred as there is no internal linkage between the flatworms’ male and female sex organs. Super effective. Super incestuous.


The phylum ‘Annelida’ includes segmented worms and leeches, and have a higher number of structures for locomotion compared to flatworms. For example, earthworms have five hearts – probably because they need to calm down with their reproductive strategy.

Two adults will align in opposite directions just like those two fabled numbers, and latch onto each other using hair-like setae for three whole hours. Each worm produces sperm and eggs and secretes them through their respective pores (seminal vessels and receptacles). The ‘collar’ around an earthworm (the clitellum) produces a mucus ring which travels up the length of the worm, picks up the eggs then the sperm like the worst Uber ride of your life. This mucus collar passes over the worm’s head and forms a hardened cocoon where tiny adults will emerge as earthworms lack a larval stage. It’s like if you took off your sweater, left it for a few weeks, and tiny adults came out – fully equipped with an opal card and a tax return. That’s how the earthworm does it.

Take from this what you will, and be careful when next walking in the rain – you now have an idea as to the absolute ordeal that your friendly neighborhood worms, slugs and snails have gone through.

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