You’ve heard the jokes. "Memory of a goldfish." We use it to poke fun at friends who forget where they put their keys or what they were saying mid-sentence. But it’s actually a total lie. Goldfish have decent memories, honestly. They can remember things for months. So, if it isn't the orange guy in the bowl, which animal with the worst memory actually takes the crown?
It’s complicated.
Defining "worst" depends on what kind of memory you're talking about. Are we talking about short-term "where did I put that" memory? Or the long-term "don't eat that berry because it’ll kill you" kind? Nature is weirdly efficient. If an animal doesn't need to remember something to survive, it just... doesn't.
The Myth of the Three-Second Goldfish
Let's clear the air first. Researchers at the University of Oxford and other institutions have debunked the goldfish myth a thousand times over. They can be trained to respond to colors, sounds, and even navigate mazes. They remember these things for weeks, sometimes even months. The three-second rule is a myth we created to feel better about keeping them in tiny, boring glass bubbles.
If we’re hunting for the animal with the worst memory, we have to look toward creatures whose brains are basically just a handful of neurons tied together with string.
Why Sea Slugs Might Own the Title
Enter the sea slug, specifically Aplysia. These things are basically the "reboot" button of the animal kingdom.
Now, don't get me wrong. Sea slugs are favorites in neuroscience labs. Why? Because their neurons are massive and easy to watch. Dr. Eric Kandel actually won a Nobel Prize for studying their memory. But here’s the kicker: their "memory" is mostly just reflex. If you poke a sea slug, it withdraws its gill. If you keep poking it, it gets "sensitized." But ask it to remember a path? Forget it.
They live in a perpetual "now." Their world is a sensory stream where the past barely exists unless it’s encoded as a physical flinch. Is that a bad memory, or just a really focused life? You decide.
The Chimpanzee’s Surprising Short-Term Failure
This one usually shocks people. We share about 99% of our DNA with chimps, right? They use tools. They have social hierarchies. They're geniuses. But in a 2014 study published in Animal Cognition, researchers tested 25 different species on short-term memory.
The results were brutal for our hairy cousins.
For many animals, including chimpanzees, a memory of a specific event—like a light flashing or a person waving—starts to vanish in about 20 seconds. If you show a chimp a piece of food, hide it, and wait 30 seconds, there’s a decent chance they’ve moved on mentally. Humans, by comparison, can hold onto that "nonsense" information for minutes or hours if we try.
But wait. There’s a catch.
Chimps actually destroy humans in "working memory" tasks. In the famous Primate Research Institute tests at Kyoto University, a chimp named Ayumu could memorize the location of numbers 1 through 9 on a screen in a fraction of a second. Even when the numbers were covered up instantly, he tapped them in order perfectly. Humans couldn't even get close.
So, does the chimp have a bad memory? No. It has a highly specialized memory. It’s built for the "right now." If you’re swinging through trees, you don't need to remember what happened three minutes ago. You need to know where the next branch is.
The Case for the African Grasshopper
If we want to find the true animal with the worst memory, we should probably look at insects. Most insects have tiny brains, but some are surprisingly sharp. Bees, for instance, are navigational wizards.
But then you have the grasshopper.
Specifically, certain types of locusts and grasshoppers seem to have almost zero "associative" memory when it comes to certain stimuli. In lab settings, scientists have tried to teach them to avoid certain smells or tastes that make them sick. While a rat learns that in one go, a grasshopper might take dozens of repetitions—or never learn it at all. They are the ultimate "oops, I did it again" of the wild.
The Hamster: 24 Hours of Nothing?
Pet owners might fight me on this one. Hamsters are adorable, but their brains are focused on two things: running and hoarding.
There is a common belief in the veterinary community that hamsters have a memory span of about 30 seconds. While that’s an exaggeration, they do lack "spatial" memory compared to rats. A rat will learn a maze and keep the map in its head. A hamster? It might run the same wrong turn tonight that it ran twenty times last night.
They don't really need to remember. In the wild, they live in burrows and forage. Their survival strategy isn't "remembering where the predator was yesterday," it's "be underground before the predator sees you today."
Sloths: The Slow Forgetters
It’s almost too easy to pick on the sloth. They’re slow. They’re mossy. They sometimes mistake their own arms for tree branches and fall.
That’s not a joke. It actually happens.
The three-toed sloth has a brain-to-body mass ratio that is among the lowest of all mammals. Their survival strategy is being so slow and unappetizing that predators just ignore them. Because they don't hunt and their food (leaves) doesn't move, their "memory requirements" are rock bottom. They don't need to remember where a fleeting food source is. The food is everywhere.
If memory is a muscle, the sloth's is in a permanent state of atrophy.
Why "Bad" Memory is Actually a Strategy
We think of a bad memory as a defect. For an animal, it's often an energy-saver.
Brains are expensive. The human brain uses about 20% of the body's total energy. If an animal can survive by just reacting to its environment rather than storing and retrieving data, it saves calories.
Take the jellyfish. It has zero memory. Literally. It doesn't have a brain. It has a "nerve net." It responds to touch and chemicals in the water. It has lived for millions of years without ever "remembering" a single thing. Is it the animal with the worst memory? Technically, you can't have a bad memory if you don't have a memory at all.
How We Measure This Stuff (And Why We’re Often Wrong)
When scientists test memory, they usually use "Delayed Match to Sample" (DMTS) tests. They show an animal a stimulus, wait, then show it two options and see if it picks the original one.
- Dogs: Can remember a command for a long time, but their short-term memory for "where did I just put that ball" is often gone in two minutes.
- Cats: Surprisingly good. They can have a working memory that lasts up to 16 hours, far outperforming dogs in some studies.
- Birds: Clark's Nutcrackers can remember the location of 30,000 hidden seeds.
When we look for the animal with the worst memory, we often find that we were just testing them the wrong way. We tried to make a fish act like a monkey.
The True "Winner" (If You Can Call It That)
If we exclude brainless things like jellyfish and sea sponges, the title for the most forgetful mammal often circles back to the shrew.
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Shrews have to eat every couple of hours or they die. Their metabolism is so high that their lives are a blurred frenzy of hunting. While they can remember the general layout of their territory, their ability to retain "non-essential" information is incredibly low. They are essentially biological machines programmed for one task: find worm, eat worm, repeat.
What You Can Learn From Forgetful Animals
It’s easy to feel bad for the grasshopper or the shrew. But there’s a lesson here. Memory is a tool, not a trophy.
- Efficiency over everything. Don't beat yourself up for forgetting "useless" info. Your brain is just being an efficient sloth.
- Context matters. You might have a "bad memory" for names but a "great memory" for faces. That’s just your hardware.
- Environment is key. Animals with "bad" memories survive because their environment doesn't require them to be historians. If you want to remember more, change your environment to make that information essential.
To really get a handle on how animal intelligence works, stop thinking of it as a ladder with humans at the top. Think of it as a bush. Every branch is "smart" enough to survive exactly where it is.
If you're curious about how your own memory compares, try a simple working memory test online. You might find that while you can remember your childhood home, you’re not much better than a chimpanzee at remembering a string of random numbers shown for half a second.
Nature doesn't care about your SAT scores; it just cares that you're still alive tomorrow.
Next Steps for the Curious:
- Check out the Kyoto University Primate Research videos on YouTube to see the "Ayumu" chimp test in action; it will genuinely change how you view animal intelligence.
- Look into environmental enrichment if you have a "forgetful" pet like a hamster or goldfish—memory can often be "unlocked" with the right stimulation.
- Read "Are We Smart Enough to Know How Smart Animals Are?" by Frans de Waal for a deeper look into the biases that make us think animals have bad memories.