Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Great personality when you get to know it (Image: Paul Kay/SplashdownDirect/Rex Features)

Species: Actinia equina

Habitat: shallow, rocky shores of the north-east Atlantic, particularly around the British Isles

Life is all about making decisions, and often the answers boil down to your personality. Do I have the nerve to quit my job? If I work in London can I deal with crowds of smelly people on buses? Am I willing to accept a hangover tomorrow morning? (Answers at the bottom of the page.)


Personality and the ability to make difficult choices seem like human characteristics, but other animals had them long before we came along. Even the beadlet anemone can boast these traits, and it doesn’t even have a brain. Yet individual anemones have distinct personalities, and they can make decisions in a remarkably nuanced way.

Personable cnidarian

“Personality” is one of those words like “intelligence” or “consciousness” that means different things to different people. But shorn of cultural baggage, it simply means that individuals consistently behave in particular ways. In that sense, animals as diverse as monkeys, fish, squid and insects have personalities.

Mark Briffa of the University of Plymouth, UK, wondered if personalities might be found even in some of the simplest multicellular animals. Sea anemones are cnidarians, like jellyfish and corals, and unlike most species that evolved later they don’t have discrete brains. Instead they have diffuse nets of nerves running through their bodies.

With colleague Julie Greenaway, Briffa headed out to the south-west coast of the UK and found colonies of beadlet anemones living in the tidal zone. He decided to look at one aspect of their behaviour: how they respond to threats.

Picking on a polyp

He threatened 65 anemones by squirting them with a jet of sea water from a syringe. In response they retracted their tentacles, closing the hole on their top surface that serves as both mouth and anus. Briffa measured how long they stayed that way before reopening.

Each anemone was tested three times over the course of a fortnight. Briffa found individuals were highly consistent, even when he factored out differences in water temperature, which slightly affected their behaviour.

Anemones are some of the simplest multicellular animals, not much more complex than sponges, so it seems personality is truly ancient and extremely common.

Anemone baiting

The beadlet anemone can also make impressively subtle decisions. When two anemones meet they fight for control over a territory. Their tentacles contain stinging cells called nematocytes that inject a toxin into their opponent. You wouldn’t forget that fight in a hurry: attacking anemones leave strips of stinging skin on their luckless victims.

Fighting is dangerous, so animals faced with an enemy must decide whether it’s worth having a go, or whether they should meekly retreat and save themselves the trouble. With Fabian Rudin, Briffa staged 82 fights between pairs of anemones and recorded how they played out.

In contests where neither anemone stung the other, the biggest generally won. If one stung the other, but the other didn’t retaliate, their relative sizes made no difference: instead it was the size of their nematocytes that predicted the outcome. But if each stung the other, the key factor was the number of strips of skin that attackers managed to land.

So the anemones can change how they make their decisions – a faculty thought to be the preserve of more complex animals like mammals. A 1979 paper entitled “The logical stag” showed how male red deer made similar decisions. Briffa has called his paper “The logical polyp” – a title he describes as “cheeky” – because the beadlet anemones seem to be just as cognitively flexible as the deer.

They’ll be on Britain’s Got Talent next.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0021963, Behavioral Ecology, DOI: 10.1093/beheco/arr125

Answers: yes, yes, go on then.

Read previous Zoologger columns: Pink magnet slug doesn’t need ruby slippers, The first non-human meat farmers, Biofuel powers biggest flying marsupial, Tough guys wear turquoise, Patriarchal fish punish powerful females, Clone army steals genes from other species, The snail that’s bust a gut to become toxic, The only fish that cries like a baby, Flashmob gathering of world’s largest fish, Genetic superpowers of the common shrew, Sea anemones spawn mixed-up kids, Colourful ducks may have fewer sex diseases.