Male bat bugs have sharp needle-like penises, which they use to stab the female bat bugs right in the stomach, even though they have a vagina. Sperm is injected directly into the bloodstream, which isn't even where it needs to go. They have been observed to even stab other males. Both genders have evolved “false vaginas” in the middle of their abdomens to make this fun hobby less painful.
Banana slugs which are hermaphrodites can be 6-8 inches and their erect penis can be just as long. In addition, their penises emerge from their heads. After mating, banana slugs eat each other’s penises.
Female spotted hyenas have the largest clitoris of all mammals. It is shaped like and larger than the male hyena’s penis. This is referred to as “pseudo-penis”. This means that it is really hard for the males to have sex with a female hyena who isn't receptive to it. It does have drawbacks though, in that they give birth to live young who have to come through that long and not too stretchy pseudo-penis. It is not uncommon for the pseudo-penis to split during childbirth and for the mother to bleed out. A lot of hyena cubs die before they're actually birthed because they suffocate on their way out.
Mayflies have a lifespan of only a few minutes and rarely live past a day. A male mayfly has two penis-like organs and the female has two sexual openings.
A small mouse-like Australian creature called antechinus literally f*ck themselves to death. The male stops eating and sleeping when mating season starts and he can mate with females for up to 14 hours at a time. He exhausts himself so thoroughly that his body starts to fall apart. His fur falls off. He bleeds internally. His immune system fails to fight off incoming infections, and he becomes riddled with gangrene. By the end of the mating season, physically disintegrating males may run around frantically searching for last mating opportunities.
Greenland sharks have the longest known lifespan of all vertebrate. They have an average lifespan of 400 years. Unfortunately for them, they spend most of this long lifespan swimming blind despite being born with fully functioning eyes. Majority of these sharks are blind due to the fact that they have parasites hanging from their eyes. These pinkish-white parasites are called copepods, and they attach themselves to the Greenland sharks’ cornea, rendering them blind.
Peppered moths evolved to blend in with tree bark. Then the industrial revolution covered all the trees with soot, so they stood out like a sore thumb and got eaten by birds. This created a selection pressure towards black pigment making them darker. They are now lighter again after pollution regulations cut down sooty coal emissions.
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Sea cucumbers spit out their guts via their anus as a defense mechanism. Also since pearlfish has no defense mechanism of their own, they hide from predators by burrowing into a sea cucumber's anus. While inside, it may eat the cucumber's gonads. Although the cucumber normally defends itself by squirting out its guts, the pearlfish does not trigger this response, possibly because it isn't worth the trouble.
19Stephens Island Wren
Stephens Island Wren had no natural predators, so evolution rendered it flightless as it didn’t need to escape. Humans arrived on the island and one year after discovery and soon after its declaration as a new species, it went extinct. The lighthouse keeper's cat killed every single one of them. It is the only species to be eradicated by a single, lone entity.
Australian jewel beetles are threatened because they try to have sex with beer bottles that look/feel like the female Australian jewel beetle and they subsequently die of sun exposure.