Sibling suckling. Why do adult domestic cats do it?

“Sibling suckling” is when domestic cats beyond the age of weaning suckle on each other for reassurance and comfort. There is a video on the Internet described as a “threesome of cats bizarrely suck on each other’s teat in unison”. It’s not quite true because in the video we see a mother and her two adult offspring. They are full-grown cats and they are suckling off each other in the 69 position. In other words, to put it another way, each of them is treating the other as their mother.

Neither of them is receiving milk but they’re doing it instinctively. Newborn kittens instinctively go to their mother’s breast for her colostrum and they pick out a nipple and they own it for as long as they use it. This prevents competition amongst siblings. And this instinctive desire can be carried forward to adulthood if the kitten is weaned too early.

Sibling suckling
Sibling suckling. Screenshot.
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Adult’s or Kitten’s instinctive reassurance behavior – comforting behaviour

Sibling suckling is a bit like a toddler sucking their thumb. Cats suck their ‘thumbs’ sometimes too! And it is the reason why, I believe, these adult siblings are nursing each other as if they are mothers. To recap, it is because each of them has treated the other as their mother and instinctively gone for their breast without any chance of receiving nourishment. And the underlying motivation is to seek reassurance that all is well. It is comforting behaviour. A lot of what humans do is comfort behavior.

Kitten sucking their thumb
This is an alternative to wool-sucking. Photo: PoC.

The mother is the pale-coated cat in the photograph which is a screenshot of the video. I can’t embed the video on this page in this instance so I’m reliant on referring to a rather poor quality still image.

The siblings are the grey/brown tabby cats you see in the picture. The people who captioned the video got it wrong. They thought that all 3 cats were suckling. It’s not true. Only the siblings were and they were doing it to each other. The mother tried to get away from it.

Obviously, it is not very helpful to either of them if they are trying to extract some milk from their breasts. It may cause discomfort and they may do some damage to each other but I doubt it.

Feline wool-sucking
Feline wool-sucking. Picture in public domain.

Early weaning

The trouble with early weaning is that it can result in unwanted behaviours in domestic cats. You see it quite a lot. Cats sucking on their owner’s earlobe is an example. Or sucking on a person’s arm, hand or neck. They can also suck on items of clothing and wool. Dr. Desmond Morris believes that the lanolin in wool makes it smell like the mother’s breast which attracts them to a woollen garment to be a mother substitute.

Wool-sucking alternative the owner’s neck. Photo: YouTube.

It’s actually a bit distressing to see. It implies that the adult cat is seeking reassurance and is anxious. It’s a bit like a child sucking their thumb for comfort. This behaviour can last for very long time and it may be permanent. Cats also suck their thumbs sometimes.

It seems that early is not uncommon and is sometimes the product of careless breeding by irresponsible people.

Keeping adult cats in a kitten’s mental state

Another supporting reason why adult cats do this is because humans keep their adult cats in a state of mind which is that of a kitten as they provide for every need as their original feline mother did. The adult cat can sometimes think they are kittens which must encourage this aberrant form of nursing at mother’s breast.

Kitten sucking their thumb
Kitten sucking their thumb. Photo in public domain.

I fostered a cat who did this on my arm. A woman adopted him and I explained his behavioural idiosyncrasy which she accepted. I believe, however, that she returned the cat later to the cat rescue organisation I was working with. This indicates that it can be a problem although I don’t know why she gave up the cat.


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