Designing an animal that wants to be eaten

Question

So I had a funny idea, somewhat based off the cow in the Restaurant at the End of the Universe in the Hitchhikers Guide. You know the one—that wants to be eaten and whose only purpose in life is to be consumed.

Plants already have a variety of similar survival solutions: to my knowledge most fruit is designed to be eaten so that the animals can then spread the seeds of the plant in their feces. However, would this be possible with an animal?

What benefit could an animal gain by being delicious and seeking out being eaten by other animals? Is there a way such an animal could use its own death to aid in reproduction?

Ideally the animal shouldn't kill the creature that consumes it (so no larvae inside the parent that eat their way out of the creature that ate their mother, for example) and the relationship / interaction should be mutually beneficial for both parties.

Answer 1

That's not too hard. There are plenty of real-life animals that want to be eaten. They're either parasites, or the hosts of parasites, whose behavior is modified by the parasite that they carry.

Of course, since you want the interaction to be mutually beneficial, your animals won't technically be parasites, but their ancestors could have been. It's also fairly common for parasites to evolve into mutualistic relationships with their hosts.

The reason for a parasite to want to be eaten is simple enough: it needs to get inside another animal in order to continue its life cycle, whether that's to trigger a metamorphosis of some sort, or because it's eggs can only hatch in a certain kind of host, or whatever. The trickier part is figuring out how eating the parasite turns into a benefit for the eater.

The obvious one is that eating the former-parasite provides the same benefits that eating usually provides--energy and nutrients--in sufficient degree to offset whatever resources the now-symbiote drains from the host. Perhaps, for example, there is a creature with a multi-stage life cycle with morphology alternating each generation, such that one generation requires a certain other animal (or class of animal) as host, and the alternating generation is free living. Now, just make the free-living morph capable of eating stuff that its host animal can't natively digest, and the host/predator species will be able to expand its nutrient base by eating the free-living generation in exchange for hosting its eggs. This is basically the same kind of relationship that humans have with goats: goats turn unfarmable land into meat and milk for humans, and in exchange for letting us eat them, we breed and take care of the goats. Pigs are in a similar situation--they turn garbage into meat, and we help them reproduce in exchange.

Another option might be starting with a mind-altering parasite, like, e.g., toxoplasma (except an animal version of it--perhaps something like an intestinal worm that has similar psychopharmacological effects as the real-world protist), and figuring out a way that its psychological effects could become beneficial. This could be completely accidental; for example, the aforementioned toxoplasma causes rats to become unafraid of cats, so that the cats will eat them, because it needs to live in cats to reproduce; in humans, it (allegedly) causes the host to become more fond of cats as well... even though cats don't typically eat humans, so its a dead-end for the parasite! Although toxoplasmosis can also cause psychological illness, one could argue that making humans fonder of cats is actually beneficial, as keeping cats around means that the cats eat rats, which cuts down on disease transmission. Maybe if more Europeans had toxoplasmosis, we would've avoided the Black Plague! Make your fictional parasite capable of reproducing in its accidental host, and you have a mutually beneficial relationship there.

Taking a more direct approach, it's possible that a parasite ends up having incidental effects on an accidental host (not the one that it originally evolved to control) that induce immediately beneficial behaviors. Just off the top of my head, it's not hard to imagine a parasite that, e.g., induces an attraction to water and bathing (because it wants to be spread through water), which directly results in improved hygiene for the host.

It is also possible that a host animal evolves over time to accomodate for the effects of carrying a parasite, such that removing the parasite actually results in pathological conditions. If, for example, the parasite is psychoactive, and the host evolves to adjust its production of neurotransmitters to function normally when under the influence of the parasite, then removing the parasite will result in abnormal function in the modern host. At that point, the former parasite is really acting as a mutualistic symbiote, helping to maintain the hosts neural function. One could argue that humans already have this sort of relationship with a lot of common microbes--lack of exposure to common microbial infections results in deficient immune function. Parasites-turned-symbiotes could also produce vitamins, useful toxins which are stockpiled by the host and used against other animals, etc.

You may have noticed that of the behavior-modification examples I came up with essentially come down to improving competition against other parasites (diseases). That's accidental (I'm sure with sufficient thought one could come up with positive behavior modifications that are also useful for a parasite, and don't have to do with parasitic competition), but that idea can be exploited more directly: perhaps the parasite is good enough at fighting off competing infections that dealing with that one parasite is a better idea for the host than leaving itself open to a wide variety of other infections. This, of course, can easily be combined with evolution through tolerance to dependence on the parasite for normal function. Note that humans also sort of already have this relationship with a lot of gut bacteria! If they get into the wrong places, it's really bad, but we like having them in our intestines because they keep the other baddies out.

Ability to carry a parasite could also be subject to sexual selection, in which case the parasite that makes an animal want to get eaten could benefit its host enormously by increasing its reproductive prospects before it gets eaten. If the parasite has obvious behavioral or physical effects, those may end up acting like a peacock's tail; a peacock's tail is a horrendously expensive feature that severely reduced the bird's ability to avoid predators, and its only purpose is to show off to peahens that I'm so incredibly awesome that I can get away with growing this impractical thing and still be alive. Your animal would be showing off a similar attitude: I'm so incredibly awesome I can survive and thrive despite obviously carrying this parasite. Now, that's something of an unstable situation because there would be pressure to evolve the expression of similar features without having to actually carry the parasite (essentially lying about fitness to get more / better mates), but it could become a stable mutualism if combined with evolution towards accommodation of and dependence on the parasite's presence, for any of the reasons described above. Then, you could end up with a "parasite" that wants its host to get eaten so it can complete its life cycle, and a host animal that wants to get eaten (after having lots of babies) because it wants its parasite to complete its life cycle--because if the parasite goes extinct, so will the host species that has come to depend on it! (For vitamins or neural function or parasitic competition or whatever combination of things.)

So, there you go. Just try to think of all the ways that parasites can evolve into mutualistic symbiotes. Then, start with an animal parasite that needs to be eaten to complete its lifecycle, but does not kill the host, or a microbial parasite that makes its host animal want to be eaten, and evolve that into either an animal symbiote that wants to be eaten, or an animal that wants to be eaten as a side-effect of carrying a microbe (or whatever), but benefits sufficiently from its symbiote before that happens.

Answer 2

Plants naturally produce edible fruit because they can't move, and animals can - animals eat the fruit, move the seeds, then defecate them out. The seeds then grow in a potentially uncolonised location (with bonus fertiliser).

Egg fruit

You can easily imagine a sessile animal (like a sea anemone) that uses the same process. It lays eggs whose embryo is safely wrapped in a tough lining, but surrounded by something nutritious and digestible - either fleshy (like a placenta) or like a classic yolk. A highly mobile animal eats the eggs, and deposits the young a long way away. You did specifically want the adult to die - in that case the adult itself becomes extra nutritious when its young (kept inside) are ready. Bonus points if the adult is normally poisonous or well armoured, to prevent itself being eaten too early.

Migrants

The adult doesn't even have to be stationary. Imagine an extreme long-range migrant, like the monarch butterfly or an eel. Perhaps the adults travel a huge distance to the breeding grounds, but the season is too short for the young to develop enough to make the return journey. They therefore hitch-hike inside a larger animal that does travel in that direction. This could be non-lethal: Logan R. Kearsley has given lots of ways for that to benefit the host. But we can come up with lethal methods too.

Perhaps only a fraction of the young survive the host's digestive juices. Enough survive to propagate the species, but enough die (giving nutrition to the host) that they are still worth taking the gamble on eating.

Perhaps the host species does exactly the same migration trick, but in the opposite direction...

Cannibalism

IndigoFenix and Denis de Bernardy have already mentioned cannibal spiders, but we can extrapolate further by looking at colonies. The (real) honey pot ant has a specialised worker caste that swells with food during good times, so that the colony can feed off them during famines. They only regurgitate the food, without dying, but a lethal version is just as feasible.

Perhaps this isn't even to prevent famine. Imagine a eusocial creature that practices mass spawning - to avoid predators, or to make use of sudden bounties of food. During most of the year, the colony collects food as normal, and the queen produces just a few young that are immediately fattened-up by other workers. When breeding season arrives, she devours them to fuel a rapid mass pregnancy or clutch of eggs, making young that are intended to survive.

Mutual destruction

You specifically didn't want parasites that eat their way out of the host. But what if the host also wants to be eaten...

In a world without flowering plants, there are no fruit. But when the parasite lays eggs in a plant, the larvae produce plant hormones that force the plant to grow a fleshy, fruit-like gall around them. The gall is toxic except to one species or group of host creatures. They gorge on the fruit-galls to gain the nutrients they need to reproduce, and they do so. But the cost is that the parent host is infected by the parasite. It will be eaten alive, eventually. But the parasite is slow, and the host makes young rapidly. The next host generation is safe and sound before their mother is devoured. Admittedly an individual host may not "want" to be eaten - not even by the standards of natural selection. But the species cannot survive without the food made by the parasites, and so the hosts must continue to sacrifice themselves.

Defense via Sacrifice

This idea works best for large herd prey animals that are themselves dangerous to their predators, like wildebeest or sauropods.  We combine the familiar concept that predators take elderly or infirm creatures from the herd, and the decoy behaviour of some animals.

When a herd is pursued by predators, the oldest or illest member may naturally fall behind.  At some point, it gives up entirely, and turns to walk towards the chasers.  It makes a special call that promises that it won't resist, and the predators run straight towards it and devour it.  If evolution is kind, the creature's pain nerves shut down when it breaks from the herd; but when has evolution ever been kind?

This strategy is superior to the real-world case where creatures do not deliberately leave the herd, because the pursuit is called off quickly when the individual makes its surrender.  This reduces the herd's energy expenditure and risk of injury.  It is also better than using a fit decoy who survives the encounter, as long as elderly animals are expendable.  This is because the predators do get fed, and thus don't hunt again for a while, allowing the herd time to move far away.

Answer 3

Truth is stranger than fiction sometimes:

https://www.nature.com/news/parasite-makes-mice-lose-fear-of-cats-permanently-1.13777

Toxoplasma gondii is known to remove rodents’ innate fear of cats. [...] its effects on rodents are unique; most flee cat odour, but infected ones are mildly attracted to it. This is thought to be an evolutionary adaptation to help the parasite complete its life cycle: Toxoplasma can sexually reproduce only in the cat gut, and for it to get there, the pathogen's rodent host must be eaten.

Voila! Such an animal already exists (sort of).

Essentially you need an animal that can only reproduce via consummation by a predator species, so at some point in its life cycle it basically goes "Eat me!" And the cat thinks itself so smug at the easy catch.

Answer 4

It's probably not that difficult, actually.

Desire to live is not intrinsic to life or even intelligence. The reason most creatures fight to survive is because that instinct allowed its ancestors to reproduce and so that instinct endured. There are organisms that die in the process of reproduction - octopus, drone bees, and mites, for instance. Some species of spiders will actively climb into the mouths of their mates, because giving an extra meal to the production of their children allows their genes to spread more effectively.

All you need to do to make a species that wants to be eaten is to selectively breed them for it. Start with a cow that is less frightened of the death of other cows than usual, and breed it. Gradually focus on this behavior until you get an animal that is attracted to places where other cows have been slaughtered, and finally one who is specifically attracted to slaughterers and submits itself to be slaughtered. If you keep breeding increasingly suicidal cows, eventually you'll get a breed of suicidal cows.

Since this suicidal behavior is what allows it to reproduce successfully, it is no different than a spider that jumps into its mate's mouth - its reproductive instinct has become linked with an instinct to get eaten by another creature.

Of course, few people in the meat industry are going to bother with this, and with more efficient lab-grown meat likely in the near future it hardly seems worthwhile, but it could be done.

EDIT: For a naturally evolving creature, the most logical course is that being eaten should somehow promote the organism's reproductive cycle. Most animals that seek to be eaten in this manner are parasites, which isn't what you're looking for - and for that matter, if the creature doesn't die in the process, the eater is unlikely to get much benefit out of eating them.

What I would suggest is a kind of "animal fruit" - a slow-moving, fatty creature with a sack full of small, hard eggs. When the creature is eaten, its body is digested but the eggs pass through the digestive tract and are dispersed long distances.

Perhaps a formerly parasitic species (like a tapeworm) that, faced with an increasingly hard-to-fight immune system, started feeding more before being eaten while shortening its intestinal parasite phase (in order to reduce the time it would have to resist the immune system) and eventually ditched the parasite phase entirely.

Answer 5

Some spider females eat the male after they're done copulating

There are known cases of spider cannibalism already, with the female eating the male (a good source of protein) after mating.

There also are a handful of examples of spider species that exhibit sacrificial mothers, that die while guarding their eggs, allowing their offspring to eat them upon hatching.

Answer 6

"Want" is a difficult trick, because to want to be eaten requires a level of intelligence.

Diseases, parasites and parasitic fungus can change brain behavior, which can result in getting eaten, but you can't really say the animal wants to be eaten as such.

Why, on the other hand, is easy. Life is about survival. If you can ensure the survival of your offspring / species by being eaten, then a species will do that.

Just look at domestication. We eat beef, chicken, lamb, fish and pork and none of these species are close to extinction--in fact, these species are some of the most numerous animals found on the planet.

We protect and care for animals, which allows them to breed and breed and in return we eat some of them.

We also breed docility into the animals, so whilst they might not want to be eaten as such, the animal is fairly dumb and oblivious to the oncoming death as much as possible. This is a desirable characteristic, as stress affects the meat.

It would be possible to breed an animal that wants to be eaten, but it would be counterproductive to current breeding characteristics.

You would need to increase intelligence as well as a self-destructive trait/mental illness. There are people in the world already that want to be eaten.

Answer 7

I can imagine a herd species that evolved a sacrificial caste. The species routinely needs to run and flee from much faster and deadlier but smaller predators. Some members of the species are known to grow much larger and plumper than others, and maturity is identified when the fight-or-flight response is replaced with an instinct to lure predators away from the rest of the herd and allow itself to be consumed, ensuring the survival of the herd at the cost of the life of the sacrifice. These creatures won't seek out danger, but will also not flee from any predator that appears, especially if there is a friendly herd nearby to distract the predator from.

Of course, once an intelligent species finds them, they selective-breed the heck out of the sacrificial caste, to the point that the entire herd are members of the sacrificial caste. Most members of the intelligent species might not even remain aware that the original members of this species had runners or other castes.

I've extrapolated this idea from the concept of mother animals leading predators away from their young and sacrificing themselves to protect them, though a very quick Google search didn't immediately reveal to me which animals it was that I'd heard have been observed with this behavior.

Answer 8

Draco18s's answer is very good! But in fact, I found something even more strange on Quora:

Some baby birds instinctively try to insert their beaks into the mouth of their mother so their mother can regurgitate food. Sometimes this is done by simply looking for a distinctive color, the color of the inside of the mouth of the mother bird, usually reddish or pinkish. In some birds the instinct is triggered by a spot of color on the outside of the beak. Tapping the beak makes the mother open her mouth so she can regurgitate food. It can in some cases be triggered by a painted white piece of plywood with a spot of the appropriate color and approximately the same size and shape. In a small animal, reproducing this instinct and coding it to the human mouth/throat means it would literally jump into a human's open mouth due to the compulsion written in its genes. A little gross and unsanitary for humans but maybe usable for some domestic animals like dogs or cats. But again, probably not what you are asking since there is no desire to be eaten per se, just a desire to go to something that looks like a mouth.

Quora Site

This could count as "purposely becoming the food of another animal," although it doesn't account for the "desire part." Just an interesting paragraph :P

Answer 9

In a magical world (or a world with magic-like effects) perhaps there's a "Inverse Ninja Law" in effect.

In this world, the "magical" power of a particular species is constant BUT the with normal, exponential biological growth the "magic" gets spread thinner and thinner among the living individuals. The individual creature, having had children, has a biological imperative to give advantage to its offspring. It goes out into the world to be eaten so that it's magical essence can be distributed among its children.

Why doesn't it just commit suicide? Because of magical reasons.

Answer 10

I think even in case of plants, the mutually beneficial aspect comes from a renewable feature of the plant. Plants produce tannin to prevent animals from eating leaves and other important parts of the plant. A plant is at an overwhelming disadvantage when it comes to mobility. So, it has to make a stronger compromise compared to animals which have mobility; which is why it gives out nutritious and sugar-filled fruits.

In the animal kingdom, human beings don't really have any outstanding ability to help other semi-intelligent animals, except ensuring they're not wiped out. In fact most animals outperform human beings in one or two aspects. For example, a cheetah can run faster than humans, and elephants are stronger. A cow can survive on relatively less-nutritious grass (and provide milk which is nutritious for humans; which is also one of the reasons why cows were domesticated) in non-forest ecosystems.

So, I'd guess as far as the tasks about which animals care, which is basic survival and reproduction, unless you're able to provide them some fundamentally awesome things, I doubt you could make them give you anything. Also, even then, it wouldn't give its life unless it's mentally dysfunctional in some way like the bacteria example by @Draco18s.

Answer 11

Larval form eats parasites and produces antibiotics

Creature keeps its baby larvae embedded in very tasty tentacles that are intended to be eaten and the creature can regrow. Sometimes predators get greedy and eat more than the tentacles, so parents can sometimes die. The tentacles provide nourishment to the creature eating them while the creature eating them provide a place for the larvae to grow.

Once eaten the larvae consume resources from their host much like a parasite till they become big enough and then get pooped out. However, unlike a parasite the larvae do earn their keep while they are in the host. Not only do they feed on parasites that may be present in the digestive system, they also produce antibiotics.

The antibiotics may have originally been intended to kill bacteria in the digestive track so that the larvae could gain the nutrition all for themselves, but over time the bacteria in the digestive track built up a tolerance to it. So if the creature has an infection or has a parasite in them, then eating your tasty animal can result in them recovering from it. It may result in some unpleasant side affects, such as fatigue and unusual looking stool, but it would be worth it.

Answer 12

It’s very easy to make animals illogically want to be eaten. But can you make them logically want to be eaten?

Teach them economics 101: people will only feed cows or allow them to graze if they’re eaten - no-one wants to keep them as pets or see them in a zoo, and cows’ milk is regarded as vastly inferior to mare’s milk.

The food market is ultra-competitive - sure beef is popular now, but who knows if it will be next year?

An adult cow that has had a couple of offspring has two choices: Live for a couple more years and then be butchered, or be butchered now. If they choose the former, sure they might get a few more years. But someone might eat that beef, decide that beef tastes bad, and then the offspring are killed off while they’re still young because no-one wants beef. Or you can choose to be butchered while you’re still in your prime, keep up the popularity of beef and give your children a future.

As a parent, which would you choose?

Answer 13

Why

There could be many reasons.. Parasites, proliferation and for me mainly safety.

Both benefitial

There exists some fishes that keep whales clean of the dead tissue and some parasites ( https://en.wikipedia.org/wiki/Cleaner_fish ).. It's mutually benefitial, so when it's possible outside, why not inside? It could be safe place for cleaners and they would make (life easier/help to survive) for the bigger animal..

One side benefitial

Other way could be for small/medium sized animals it could be just for safety reasons.. Inside the other animal they could be safe. Further more their offsprings would have better chance of surviving the vulnerability of their childhood against outside prey. And when older they would get out inside feces. So benefitial for one side, the other side would be just carier.

Answer 14

Periodical Cicadas and their predator satiation adaptation can be considered real-word example of this behavior. These insects spend the majority of their lives underground as nymphs, but emerge in massive numbers as adults during their short reproductive period and act as easy prey.

Normally (as nymphs), there is no benefit to being eaten. However, during the short mating period, the adults emerge in billions, flooding and blanketing the environment. They are nutritious, slow, clumsy and easy to catch, almost offering themselves up to be gorged upon by their predators. Why? By achieving over-saturation in a local environment, they can feed all of their predators so that the remaining adults can breed undisturbed.

Answer 15

I think a symbiotic relationship could benefit both. Look at the babelfish - it benefits by having something to "eat" and the human benefits from the translation. Another example is Dax (that symbiont from Deep Space Nine) - its intelligent but needs a host for motion and sensors and the host gets the memories of all the previous hosts carried by the symbiont. The only difference is that we want the symbiont to be eaten so it only works if the one that gets eaten stays alive which implies a small creature.

So my idea:

You eat this small creature and it gets some benefits: it gets to travel over greater distances than it can accomplish by itself, food is delivered to it, it has somewhere safe away from its predators, and/or it has somewhere warm/cold to stay when temperatures are more extreme than it can handle, plus maybe it gets to tap into the nervous system or something so it can communicate to the host. Why? Well, maybe food is scarce and a small creature can't cover enough distance by itself to get enough food to survive. Maybe it needs somewhere safe to hibernate in the winter - it could leave when it wakes up. Maybe it's just lonely and needs intelligent communication with the host.

The host would get benefits too: it could get disease/infection protection even if the creature was hibernating but also if the creature can tap into the nervous system or something and they can communicate then maybe the brains can work together on solving problems - then the host gets much more processing speed or a different kind of processing or even just memories of previous hosts which would help make decisions.