Rare enemy effect

The rare enemy effect is a niche but interesting phenomenon in predator-prey interactions.

Consider the case of earthworms. Their number one enemy is the mole (a mole eats almost its body weight in worms each day). So the worms have adapted to recognize an approaching mole by sensing the vibrations of its feet as they dig in the soil. When they sense it, the worms escape to the surface, where mole encounters are unlikely.

However, other predators of worms have figured this out. For example, seagulls perform a "dance" to vibrate the ground, bringing up unwitting worms to the surface, ready for snacking. Wood turtles do a similar thing. Humans, in a process called "worm charming", plant a stick into the ground and vibrate the stick to summon the worms, often to collect them for fishing (but some do the process for fun and sport).

The rare enemy effect happens when Predator A exploits the prey's anti-predator response to Predator B (the main predator). It must be that Predator A is a rather rare encounter to the prey (hence the name of the effect); if they were a main predator, the prey would eventually develop an anti-predator response to them, too.

If you look closely, you can see a similar effect in the human realm, too:

• One (rather known) trick burglars may perform on you is very similar to what seagulls do. Imagine a man in a suit knocks at your door, informing you that burglars have been spotted in this neighborhood. But you can protect yourself by buying his company's security system. Worry not - before you commit to anything, he can do a free security assessment right away, inspecting potential points-of-entry (and where you keep your valuables). Your anti-predator response is to protect yourself from the burglars, so you let the man in. Whether you sign any contracts or not, you may find your house broken into within a few days.
• A similar scam happens digitally all the time. You receive an email, saying that your passwords or information security is in danger, and scammers can steal your money or data if you don't act. Of course, acting in this case means paying another scammer, or giving him access to your or your company's accounts, where he will change all passwords and require ransom to let you back into your own systems.
• Naturally, there are legal forms of exploiting one's anti-predator response, namely fear-mongering advertisements or the exaggerating (real) door-to-door home security salesman.

And do not think that these processes are limited to capturing your money; they want your support, information, attention and time, too. If there's a predictable anti-predator response, there's someone who exploits that response, legally or illegally.

• Another example of the rare enemy effect in nature