Thread by @Kristin_Hook

It may surprise no one to learn that as a scientist with a PhD in animal behavior, I keep the company of nerdy friends who like to host PowerPoint parties and drunken lectures. Lucky for you, I’m here to share my latest one that was a hit. I present to you:

5. Sneaky-f&$*%er males

This is an *actual term* used by biologists. Here’s the sitch. You might look at this image and think this is a nice happy fish family.

But you’d be wrong.

In some animals, like these plainfin midshipman (which, by the way, sing!), large males (middle) defend territories for building a nest & keeping their young safe. Attracted by their hums, females (right) choose between these large males & release their eggs in their territories.

BUT this little bugger - a sneaker male - does not defend territories or care for eggs. Instead, these males mimic females to dart between territories and secretly release their sperm into nests to fertilize eggs!

One of the craziest thing about these lurkers is that they may be small in stature, but they often have very large testes and so produce a significantly greater amount of sperm than the larger nesting males.

THE WORST!

4. The male plant bug

In most animal species, females are not monogamous. Not by a long shot. And by mating with more than one male, she creates a situation in which males have to compete with one another.

This happens both *before* mating, in which males court females and strut their stuff to try to convince her to mate with him

and this happens *after* mating at the level of their sperm, in which sperm compete with one another within the female to try to reach and fertilize her eggs!

As a result, evolution has favored traits in males that allow them to outcompete their rivals in sperm competition, including behaviors that outright try to stop it from happening.

One such behavior is called 'mate guarding', where a male does things to make sure a female he has mated with doesn't mate with other males afterwards.

For example, he can do so physically by sticking right by her side after mating - even for obscenely long amounts of time

Males can also mate guard passively by leaving things within her after mating - such as a 'mating plug' made of jelly-like secretions or their actual genitals! - to literally block another male from being able to mate with her.

Enter the male plant bug.

They passively mate guard females through chemical means, BY LEAVING BEHIND A STENCH THAT MAKES HER UNATTRACTIVE TO OTHER MALES

That's right. These "anti-aphrodisiacs" are transferred to females with their sperm during mating, and they repel her would-be suitors.

But good news - there's evidence that females make anti-anti-aphrodisiacs in turn to thwart the male's attempt to put a chastity belt on her.

3. Male dance flies

Some male insects give gifts to convince females to mate with them or to mate for a longer amount of time. Maybe a nice prey item. Or water in their ejaculate if they live in an arid place. Or their body for her to eat – if their lady is a sexual cannibal.

But in the dance fly, there are cheater males whose "nuptial gifts" are just a silk balloon.

No prey, nothing of nutritional value, just a whole lot of worthless NOTHING.

SIR, HOW DARE YOU?!

2. Slave-making ants

What you’re witnessing is a slave raid. You heard me right.

Slave-making ants are ants that capture and enslave the young of other ant species to increase the worker force of their own colony!!!!

📽️cred: @julie_serena

These poor grub grow up in another species' colony, imprinting on their smells early on and so never knowing that they belong to another species.

Doing what ants do, they go to work, but sadly are doing so for a species that has enslaved them!

While all of these examples have so far been terrible, I think the last one easily slips into number one because it involves

1. Killer fledglings of the common cuckoo

There are several examples of animals that are "brood parasites", meaning they pass off childcare to others that they have manipulated into doing so.

Some do so within their own species. Others do so for different species entirely.

The common cuckoo is a brood parasite that lays its eggs in the nests of other bird species.

Their eggs (top) remarkably resemble those of their hosts (bottom), making it hard to tell them apart!

Once, they hatch, these parasitic birds can do really terrible things to the host's own offspring, including removing their eggs from the nest or outright killing them to remove their competition!!!!

📽️cred: Artur Homan (from Rhythms of Nature in the Barycz Valley)

The hosts are sometimes none the wiser, raising these chicks as if they were their own, bringing them more and more food based on their loud cries to keep up with their quick growth and often much larger body sizes!

They have no idea they are raising a parasite.

Silver lining: in some species hosts have evolved strategies to "fight back" and use clever clues to figure out which offspring are its own - leading to an arms race between the parasite and the host.

There are plenty of other examples of assholes in the animal kingdom, but I hope I've convinced you that these five are some of the absolute worst!!!

Fin.