Why did my rat kill and consume the new baby?
This isn't a question I hear very often but when I do hear it, the person asking the question is frantic. Their favorite rat in the entire world, the most docile rat in the entire world, etc appears to have killed and eaten the little baby that they just put in the cage with him or a long-term close friend. Why would such a nice rat do such a thing? Is he now more inclined to attack other rats? To attack us?
Well, it's really not as bad as it seems. The one thing you need to remember is that before the rat(s) made a mess of the corpse by eating his/her brain or digging through his/her stomach and dragging the whole lot around (or whatever disgusting scene they managed to create for your viewing), the rat who was picked apart was dead.
"Well, how do you know?" And some of the more common accompanying comments: "It looks to me like they killed him so they could eat him." "They had plenty of food, there was no shortage of water, but I'm sure my rat(s) were blood-thirsty!" "The whole thing is awful." "I'm going to put them all down!"
I know, and you'll know, because we can see the scene of the crime. It's horrible: One of our best friends was (apparently) shredded mercilessly and it's a terrible thing to look at, but put your mind in horror movie mode for a moment. When someone in a horror movie is stabbed, what happens?
Answer: Blood spurts out everywhere! Indeed. If you were to start tearing me apart to eat me, my heart would still be beating and a beating heart pushes blood out with a good amount of pressure. It splatters and it can splatter pretty far.
But you didn't see splatters - very obvious, very dark dots of blood. You either saw no blood at all or smears of blood along sides of boxes, hammocks, toys, etc. And smears just mean that someone was dragging something somewhere.
"OK, fine, so s/he was dead first, but why would my rats do such a thing?"
The answer: Instinct. While far separated from their wild origins, there are certain habits rats have picked up over time - habits that have bolstered their chance of survival as a species.
Starting with an example: That tail is just the right length. Somewhere along the line, some rat(s) were born without tails (as pets, where survival depends predominantly on us, some are bred to be tailless). There are some drawbacks if you are a rat without a tail: Without the tail, they can't regulate their body temperature, they can't balance well, they can't jump as effectively. These "lacks" resulted in their demise and the tailless variety never perpetuated in the wild. A lack of tail apparently had no benefit either. After all, those who can adapt survive and the others do not (the basis of Darwin's theory if you missed it in school, which, if you're in the US is probable and quite likely).
Now think of the tail thing with respect to corpses. You have a colony of rats who don't consume the dead but rather leave them lying around. Death smells. Predators are now attracted to the smell and the entire colony is quickly eliminated. But somewhere along the line, some rat somewhere "figured out" that if the body is removed, the smell of death never comes to be, and the predators have a lesser chance of finding the nest or burrow. That someone and his offspring and anyone in his colony who learned the lesson from him now have a better chance of living to see the next day than the guys and gals in the burrow down the street who keep their dead lying around. And these individuals mate within their own established colony which makes their colony "stronger" (adaptively-speaking) and thus more likely to survive.
Your rats are descendents of the survivors: The ones who figured out that consuming the dead had some benefit that increased their chance of survival, of passing their genes onto the next generation.
"So why don't all the rats do this then?"
Well, we've got a good deal of separation between their wild relatives and our spoiled brats. There's obviously no threat as we, as humans and as those who select the pet rats who are brought into this world, do protect our bubs from predation. Out of laziness or whatever, most of them just don't "think" about survival. But apparently, because you're not alone in seeing one of your rats in pieces, something lingers, something instinctive, that causes some rats to follow some instinct that tells them to consume the dead. The brain, for example, is very high in protein. In the wild where food is scarce (and likely to bite back), an "energy bar" in the form of brain is quite useful. So in addition to avoiding attracting attention, there are additional survival reasons for doing such an (apparently) awful act.
If you don't believe me about this whole instinct thing: For grins I decided to get our rats a Durian fruit. After cutting it open I was certain the rats would hate it. It was the most foul-smelling disgustingly slimy thing I had ever had the opportunity to encounter. But it is something that their wild ancient Asia-dwelling relatives may have eaten and I found that, in fact, this must have been the case because not one rat, not even the most finicky rat, not even for a moment, resisted this fruit. They attacked it like I attack chocolate: Instinctively and with fervor.
Rats only eat things that they perceive are safe. Smelly sweat-sock fruit isn't something I'd consider "safe" and, in fact, I would be rather concerned about consuming smelly sweat socks because the smell would likely be due to the presence of bacteria and/or fungi - things that could hurt me - right? Besides, even the more curious and open-minded of rats won't just devour something. First they try a small portion. If it doesn't make them sick and they liked it, from that point on they'll eat as much as they like. And if you ever had a finicky rat, you know you can give those guys (and gals) the yummiest things in existence and, defying reason, they won't touch it.
So why would they do that? Why would they, all of them, even the most finicky of the bunch, devour a food substance that they've never had before and do so without caution? The best explanation would be instinct. Durians don't really smell like anything they've ever consumed. They don't taste like anything they've ever consumed. And yet they ate it like they were familiar with it...as if it were somehow innate to them...as if that particular flavor was just trustworthy and safe.
...just like the consumption of cagemates thing. It's just somehow innate to them. And it doesn't make a bit of sense to us as this habit serves no logical purpose in the pet population, but it still happens, going against any line of (human) reason we can come up with.
"Hmm, fine, it's instinctive. Are they going to start becoming more aggressive toward their cagemates? Are they going to do this again?"
No, and probably not. No, their behaviors won't otherwise just change. We bury our dead but we don't respond to social encounters with the living by shoving them in a box and throwing mud on them. In other words, they'll still be the same sweet guys and gals you had before the "massacre." They may, however, treat future corpses the same way. In my experience, however, a given group would only do this once, or never, and I can't really explain why, if it's somehow innate, they wouldn't repeat the behavior (or why, if it's innate, they wouldn't all do it): Maybe it was timing and I managed to remove their dead before they noticed. Or maybe they just didn't really like it and serving no purpose they didn't see fit to do it again. But if they consume their dead once, it could, logically, happen again. I just wouldn't expect it.
"Are they going to become more aggressive toward me now that they have a 'taste for blood'?"
Nope. Nothing changes. The behavior is situation dependent and you're not dead and stinking up the place, so I wouldn't expect them to behave any differently when interacting with you.
And, no, there's no such thing as a acquiring a "taste for blood" - If you eat a steak, you are not now more inclined to run out to grab a scampering squirrel so you can tear at his flesh "for fun," right?
P.S. If you were trying to figure out why mom or dad killed an unweaned baby, click here.
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Disclaimer: There are many non-sarcastic accounts and tips on the web regarding rat care. This is not
one of them. These are merely accounts of our experiences with rats, our perceptions of these experiences, where we've failed
and where we've succeeded. These accounts are here for two purposes: