Why do cats groom or lick each other?
Two of your cats are entwined on the carpeting, licking each other.
Aw…you think. It must be love.
Well, it’s cats, so it’s a little more complicated than that.
The behavior you’re witnessing has a special name, and it means something specific to cats. What we humans think we’re seeing when we see two cats lovingly grooming each other is probably not what’s really going on.
What is it called when cats are grooming each other?
You’d think “grooming each other” would be the perfect way to describe what cats are doing when they’re grooming each other, but it’s not.
There’s actually a scientific term for it: allogrooming, and it’s not just cats who do it. In fact, one scientist who studied allogrooming documented 44 different animal species who allogroom, including birds, and even people.
The reason this behavior has a special name is because it’s not usually just about grooming. It’s a social behavior that social animals – and yes, cats are social animals – perform for many reasons. Grooming, which is about hygiene, isn’t necessarily the main point when it comes to allogrooming.
Now, allogrooming does help animals who live in groups have cleaner bodies and thus be healthier. Allogrooming baboons showed an increase in red-blood cell counts because they got fewer ticks and thus fewer tick-borne diseases, thanks to the attentions of their meticulous baboon friends. Macaques (a kind of monkey) who social groom have lower heart rates. Rats who allogroom develop fewer mammary tumors and live longer. But there are critical social benefits to allogrooming, and those are usually the main reason to groom another member of your group.
What do cats do when they groom each other?
Before we get into why cats allogroom, let’s describe what allogrooming looks like.
Allogrooming is a behavior in which one cat licks the other cat, usually on his head and neck. The “groom-ee” is usually very willing and helpful, turning his head this way and that, so that the groomer has easy access to all his parts. The recipient of all this attention may be purring happily away through the whole thing.
One cat may request an allogrooming session from another cat by approaching with an outstretched neck, or a head turned to the side, as if to say, “hey, could you groom this spot behind my head?”
But that might be too bold at first. The cat who would like to be allogroomed might send out a friendly smoke signal first, before approaching. Sticking a tail straight up in the air, for example, tells the other cat, from afar, that she has friendly intentions.
If the other cat is also feeling friendly, he might stick his tail straight up in the air, too. The pair can then advance to the next step together: they might rub their tails against each other, or entwine them. Or they might rub their whole bodies against each other, a separate behavior called “allorubbing.”
And then they might engage in allogrooming.
Why do animals allogroom?
Allogrooming, across a wide range of animal species, is usually about keeping the peace within a group of social animals. Things can easily get out of hand when you get a bunch of anything living together, so there are gestures, like allogrooming, that help resolve or avoid conflicts, reinforce the bond between group members, and affirm social hierarchies.
Cats may be social creatures, but they became social animals relatively late in the evolutionary game. Dogs, by contrast, were living in packs from the get-go. They’ve had tens, or even hundreds, of thousands of years to evolve as social beings with complex social hierarchies and well-developed communication skills.
The ancestors of our house cats, on the other hand, were solitary animals. Cats only domesticated themselves 10,000 to 5,000 years ago, which is a blip in evolutionary time. We say “self-domesticate” because they adapted themselves to living with and around humans, to take advantage of the resources we could offer them: namely, barns and granaries with lots of mice. But living around humans also meant living around each other.
Cats are very different than dogs who, when in groups, exist in relatively complex, well-structured dog societies. Even large cat colonies are only loosely organized. There might be a dominant older female, but the hierarchy of the rest of the group will shuffle day by day.
So, cats don’t have a specific “place” in cat society. And they don’t have the kind of intricate body language and signals dogs use to communicate their intentions to each other. But cats do have allogrooming, which turns out to be a pretty handy communication tool to have in your kitty toolbox.
Why do cats allogroom each other?
If you just go by what you see, you assume that cats who are licking each other are either expressing love for each other, or care that their friends have clean fur. You can’t always go by what something looks like, though, especially when it comes to cats.
One scientist from the University of Leiden in the Netherlands was really interested in finding out why cats allogroom, and so he studied a colony of 25 cats who had been living together for a number of years to get some answers.
In his study, the stronger, bigger, and more dominant cats groomed the smaller, weaker cats. Grooming tended to be a one-way street: the groomers didn’t usually become the groom-ees, which suggests that allogrooming probably isn’t about cleanliness.
He noticed that many grooming sessions started with or ended with some aggressive behavior, like chasing, growling, or lashing a tail. He concluded that allogrooming is a way for cats to safely channel aggression, so that nobody gets seriously hurt and the group is able to live together more peaceably. 
A later study found that cats who are related to each other were more likely to groom each other than non-related cats. And if a cat is living among non-relatives, they’re more likely to allogroom with a cat they are more friendly with than one they are less familiar with. The conclusion of this study was that allogrooming is a way for cats who are already kin or close associates to reaffirm their bond.
It is likely that cats groom each other for a number of reasons: it’s a great way to diffuse tensions amongst cats living in a group, and it’s also a great way to reconnect with someone you’re already close with.
So maybe, it is a little bit about love afterall.
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