Traumatic Insemination: 7 Animals With Horrifying Mating Practice


Traumatic insemination is a bizarre mating practice in which the male pierces the female’s abdomen with his aedeagus to inject sperm. The sperm travels through the wound into her hemocoel which is the cavity that contains the hemolymph. Then it travels through the female’s hemolymph and eventually reaches the ovaries, resulting in fertilization. Bear in mind that the females never agree to this mating practice, and it is done by force most of the time. Below are some of the animals that practice traumatic insemination as their mating habits.


image: pxfuel

The annelids are a family of segmented worms, and there are roughly around 15,000 species or more in total. An example of some of the species that practice traumatic insemination is the Macrostomum Hystrix, the free-living flatworm. Just like other flatworms, this species is also a hermaphrodite which means they have both male and female sexual organs. When mating, one free-living flatworm mounts its partner and stabs its needle-like stylet through the other flatworm’s skin. Then it ejaculates directly into the partner’s body, having the sperm competing with other males’ to fertilize the female.

The female flatworm can exert her own control by selectively moving the sperm of males she does not want. Simply put, she can choose who she wants to fertilize her eggs which is an evolved behavior. Speaking of sperm, a flatworm’s sperm does not have the shape of tadpole like a human sperm. The front of the sperm has a feeler that it uses to anchor itself in to the walls of the female genitals. Then there are 2 large backward-pointing bristles that aid more support to keep the sperm in place.

2Bean Weevil

Things are absolutely horrifying during the mating rituals of the bean weevils. Male bean weevil damages the female genital tract with their spiny intromittent organ during copulation. Each male can transfer thousands of sperm to the female during a single mating. The sharp spines on his penis can damage the reproductive tract and reduce her lifespan. This also results in a low-frequency mating strategy for females or even for the species.

However, males with longer spines achieve greater mating success in sperm competition by reducing the female’s genital damage and her willingness to mate. The downside is that longer genital spines cause more harm to females and lower their lifetime reproductive success.

3Bed Bug

Traumatic insemination is one of the most fascinating traits about bed bugs as they famously do it. The thing about bed bugs is that the males have an “intromittent organ” with the sole purpose of traumatic insemination. This special organ is not only sclerotized but also curved and needle-like so that it can puncture the female’s exoskeleton. As for the female bed bugs, they also have a unique organ called “spermalege” to handle the males’ antagonistic traits. This spermalege has both the ectospermalege and the mesospermalege that are ready for traumatic insemination.

When a female is ready to mate, her large post-feeding body volume will start to show. A female bed bug receives an average of 5 trailing inseminations, but not necessarily from the same male. During mating, a male bed bug inserts the intromittent organ into the female’s ectospermalege and pierces the pleural membrane. Then he injects the sperm into the mesospermalege that contains hemocytes. This mating ritual will leave wounds at the injection sites, and a melanized scar forms when the sites heal.

4Fruit Fly

Male fruit flies have appendages on their genitals that inflict wounds on the female fruit flies during mating. As for female fruit flies, their bodies have both intragenital and extragenital (abdomen). The structures of the male genitalia puncture the female abdomen, both dorsally and ventrally outside the genital orifice. After piercing through the female’s body, the male fruit fly transfers his sperm through the wounds using the oviposition appendages. This simply increases the immediate oviposition rate and unreceptive to remating while reducing female longevity and lifetime fecundity.

5Sea Slug

At least 5 sea slug species practice traumatic insemination in their mating rituals, the hermaphrodite ones, of course. Some species penetrate each other in the head while making babies, and that is clearly something new. Hermaphrodite sea slugs have both male and female genitals, allowing them to simultaneously penetrate each other. These sea slugs inject prostate fluids into the body of their mate using their genital appendage during mating.

The interesting part is that wound infliction and ejaculate transfer through the wound involve different structures. This helps to prevent the costs of traumatic injections to increase the high production rate.


Love dart is always the first term to describe the process of sex in common garden snails and other snail species. Snails are hermaphrodites, and each of them has a love dart covered in psychoactive mucus. The male stab the female’s special organ using his syringe-like penis and then copulates with the wound. His sperm then swim directly to the ovaries through the body cavity, and the entire process is traumatic insemination.

Similar to some animals in the kingdom, female snails can eject or filter unattractive males’ sperm chemically if they want to. However, the males also have their own resolutions to win the females’ methods. Penis-stabbing is the approach that the males use to inject their sperm directly into the females’ body fluid. This could injure his partner, but at least the male can prevent her from excluding his sperm or mating with others.

7Woodlouse Hunting Spider

Harpactea Sadistica aka woodlouse hunting spiders have quite bizarre courtship rituals, the last name “Sadistica” says it all. At first, it nicely begins with some dances and hugs between the male and female. It is adorable for the male to gently tap the female with his front legs and then embrace her. The sadistic part begins when he bites her and maneuvers her into position as the female becomes passive. In case you don’t know, a male spider’s genitals are next to his head.

The penis of a woodlouse hunting spider has a needle-sharp tip known as an embolus. This embolus sits at the end of a loop called the conductor where he hooks the embolus to steady it. Once he is in the position, he drives the point straight through the female’s underside and ejaculates directly into her body cavity.

I forgot to mention that he has two penises. And I also forgot to mention that he does it six times on average. A male woodlouse hunting spider moves slowly downwards and alternates between his two awesome penises, lasting about 15 minutes. My description does not do any justice to the actual male spider’s kinky quirk, so below is a video for you.

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