Category Archives: In English

Did you know that snails have thousands of little teeth?

Teeth of a sea slug – walking sea hare (Aplysia juliana).

Snails and slugs can eat practically everything. Some eat fresh plants, to the despair of gardeners, me included. Others eat live animals, such as earthworms or even other snails, animal waste, rotting vegetation or fungi. Some species eat one type of food, others are less picky, but practically all lands snails and slugs use their tiny teeth when feeding.

Snails* don’t chew their food before “swallowing” but scrape it up and rasp it using a structure called radula. It is a somewhat similar to our tongue, but covered with many rows of tiny teeth. The snail sticks its radula out to scrape the food. If the food is in a larger piece, e.g., a leaf, snails can cut it with their jaw (snails only have an upper one) before rasping it.

Snail using its radulae to obtain food – teeth shown as zig-zags

The number, size, shape and distribution of the teeth on radulae differ between species. Some snails have more than 100 000 teeth. The properties of the teeth depend on the type of food a snail eats. The shape of the teeth can also vary across the radula.

Radula and individual tooth of a predatory ghost slug, Selenochlamys ysbryda
Teeth of an omnivorous garden snail Cornu aspersum

The teeth are made of chitin – the same biopolymer from which the external skeleton of insects is made. They can also be hardened by minerals like iron, silicon, calcium or magnesium. the teeth at the front of radulae are used the most and thus wear out the fastest. But new teeth are constantly growing at the back, to replace the worn ones.

Snails grazing on algae from a hard surface (like glass) leave a characteristic trail:

 While on a soft fruit or mushroom, they leave less regular marks:

The text above refers mainly to land gastropods (snails and slugs) as all of them (with one known exception) have radula. But this structure is present in many other molluscs, for example aquatic gastropods and cephalopods like squids and cuttlefish and in reduced form in octopuses.

* For a better flow of the text I only write snails, but I mean snails and slugs unless specified otherwise.

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Photos (in the order of appearance): RME-OT Caracas- Venezuela; Debivort; Amgueddfa Cymru; Krings et al. 2019; Magdalena Kozielska-Reid (two last photos).

Did you know that jays fall for magic tricks and don’t always like it?

Eurasian jay

Some time ago, a video of an orangutan vividly reacting to a disappearing fruit trick circulated on the internet.

Besides collecting YouTube likes, showing magic tricks to animals can also help to understand animals’ cognitive processes and their perception of the world.

Recently, scientists studied how Eurasian jays (Garrulus glandarius) react to magic tricks and unfulfilled expectations. Jays are corvids – a group of birds known for their highly developed cognitive skills. They even use tricks themselves – when they know they are being watched, they act as if they are hiding food in many places, but only truly do so in some, cleverly manipulating the food with their beak.

Recently, scientists showed jays a trick in which they pretended to insert a treat in one of two plastic cups, but actually hid the treat in their hand, just as a magician would do when trying to fool people. They then turned both cups upside down and the bird could turn them over to get the treat. The trick was that beforehand, the scientists had already put a treat into the chosen cup, either of the same kind as they showed the jay, or a different one. If they put in a different one, it could be either more or less desirable to the particular jay than the shown treat.

The trick of ‘swapping’ food. Diagram from the original article

The jays consistently picked up the cup into which the scientist ‘inserted’ the food, but reacted differently depending on what they expected and what they found. If the birds found the same treat that they ‘saw’ being placed in the cup, they just ate it quickly, regardless of whether it was their favourite treat or not. However, if the bird found a better treat under the cup than the one the human showed to it, it took a little longer to eat it and sometimes the jay would look into the cup as if to check where the expected food was. However, the most dramatic reaction occurred when the bird expected a favourite treat but found an inferior one. Then it often checked the cup again, looked under the other one and in about half of the cases did not eat the food at all (even if it would normally eat this treat when it was expecting it).

This strong reaction to an unpleasant surprise is similar to how humans react when they lose something. No one likes it if they are promised something but they don’t get it. And just like in humans, those jays that were more dominant showed stronger dissatisfaction – they were more likely to reject food that was worse than they expected.

I am curious to see what future experiments using magic tricks will teach us about animals.

If you want to see recordings from this experiment, click here.

Jay photo by Steffi Wacker from Pexels.

Do you know how to discriminate male and female houseflies?

A woman walked into the kitchen to find her husband stalking around with a fly swatter.

“What are you doing?” she asked.

“Hunting flies,” he responded.

“Oh. Killing any?” she asked.

“Yep, three males, two females,” he replied.

Intrigued, she asked, “How can you tell?”

“Three were on a beer can, two were on the phone.”

You could amuse your friends and family by telling this joke – or you could amaze them by actually correctly determining the sex of any present houseflies. Read on if you want to learn this “party trick”.

During my PhD study I examined thousands of flies, and counted males and females (I worked on sex determination), so I know what I’m talking about. In the lab, conditions made it an easy job – I could sedate the flies with CO2 and could even use a small microscope to have a better look. But no microscope is necessary if you can get close enough to a fly (or have good eyesight). And if you don’t swat too hard you should be able to distinguish the sex of the corpse. However, I challenge you to determine a fly’s sex when it’s still walking on your table, window or sleeve. It is possible!

Now the most important part – what to look for: you can look a fly between the eyes and/or at the bottom part of its abdomen (the rear part of the body; see the picture below).

Difference between female and male housefly – first column: the head viewed from above; second column – end of the abdomen viewed from below. Figure from Dübendorfer et al. 2002.

The female housefly’s eyes are set further apart than males. Their abdomen is rounder, but pointy at the end and very lightly-coloured when seen from below (lighter that seems on the picture above). On the picture the female’s ovipositor is shown, but it’s usually hidden when she is not laying eggs.

The male’s abdomen is in general slender and has a blunt end. When viewed from below it has a clearly visible dark spot at the end.

And now a small “dry” test before you start your own observations in “the wild”:

Quiz: For each photo determine whether it shows a male or female fly. For the answers see the comment to this post.

The text above concerns the housefly (Musca domestica) – common, blackish fly approximately 7 mm long. I don’t know how to distinguish males from females for all flies (there are 125000 species described), but the eye-distance rule does also apply also to several other flies (e.g. horseflies), and the genitals of many flies look similar. So, using what you learned above for other flies is a good first guess.

Photos: USDAgov –, Public Domain,;  Sanjay Acharya – Own work, CC BY-SA 4.0,; Judgefloro – Own work, CC0,; Muhammad Mahdi Karim – Eigen werk, GFDL 1.2,; James Lindsey at Ecology of Commanster, CC BY-SA 3.0,; Muhammad Mahdi Karim – Own work, GFDL 1.2,

Did you know that cuttlefish show self-control?

Common cuttlefish (Sepia officinalis)

While working in the lab, behavioural ecologist dr. Alex Schnell noticed a curious behaviour of Franklin, one of the cuttlefish. In the morning when Alex would enter the lab to start experiments, Franklin would drench her with water she ejected through her syphon. However, in the evening when Alex would come to the lab to feed the cuttlefish, Franklin would not “attack” her. Alex started wondering whether this behaviour was a sign of simple associative learning of mornings with experiments that the animal didn’t like and evenings with a meal. Or maybe it showed something more: self-control and resistance of the temptation to drench the scientist in the evening.

Franklin inspired Alex Schnell and her colleagues to test whether cuttlefish can show self-control.

Marshmallow test for children

In children self-control (the ability to delay gratification) can be tested using the so-called marshmallow test. A child is seated in a room with just a table and a chair. In front of them the experimenter leaves a marshmallow (or another treat) and tells them that they can eat it straight away or wait for a while when an experimenter leaves the room. They are told that if they wait, they will get another treat later. In the original test children waited on average 3 min before they eat the treat, but self-control increases with age.

… and for cuttlefish

Although one can’t just tell cuttlefish to wait, the researcher devised an experiment that could test for self-control in these animals. First*, they taught six cuttlefish that one compartment in their tank provides less-tasty food directly, while another compartment opens only after a delay, but contains their favourite food. Both compartments were transparent, so the cuttlefish could see both food items. Further, whenever the animal ate from one compartment, the other one was emptied of food.

Once the cuttlefish seemed to understand the rules, the real test started. Both compartments were placed in the tank and an individual was positioned at an equal distance to them. The delay for opening the compartment with favourite food was increased between experiment, causing some animals to give up and just eat the less-tasty prey. All cuttlefish were willing to wait at least 40s for their favourite food. However, many cuttlefish waited for more than a minute and one even two minutes – close to young children’s score. Interestingly, like children, chimpanzees, dogs and parrots, some cuttlefish seemed to try to distract themselves from the temptation of the direct reward, by turning away from the directly available food item.

Why wait?

A high degree of self-control has been shown for example in chimpanzees, corvids (birds from the crow family) and parrots. This was usually explained by the animal’s highly social lifestyle, long life and ability to use tools. After all, to keeps social bonds healthy sometimes it’s better to let others eat and delay one’s own gratification. Tool use also demands waiting for all the components to be assembled before it can be used. However, a cuttlefish lives for only two years, is not particularly social and does not use tools – so what could explain its self-control? Dr. Schnell speculates that it improves the foraging success of cuttlefish. They often lie motionless, camouflaged, on the sea bottom. Waiting for their prey to get close enough not only increases their attack success, but also reduces the chances of being seen by predators.

For a long time, people though that only humans have self-control, but this is definitely not the case; instead, it seems to be widely spread in the animal kingdom.

* Here I explained only the core of the experiment. The whole experiment was more complex and can be found in the original paper.

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Photo: By Jarek Tuszyński / CC-BY-SA-3.0 & GDFL, CC BY-SA 3.0,

Did you know that bumblebees find efficient ways to move a ball to a target?

Have you ever watched a bumblebee collecting nectar from flowers? At first sight, this does not seem like a very difficult task, requiring sophisticated cognitive skills.

However, bumblebees have an amazing ability to learn. Not only where to find the nectar, but also how to perform human-designed tricks that require behaviours not needed in nature. For example, bumblebees have learned to pull strings, pull caps aside, and rotate disks to get to a reward.

Not so long ago, scientists (and bumblebees) have taken it a step further. The scientists, in various ways, demonstrated to their subjects that moving a ball into a target (a circle drawn on the experimental platform) led to a reward. The bumblebees quickly learned to do so themselves, and even improved their tactic to be more efficient than those demonstrated.


First, the researchers trained the bumblebees to move a wooden ball, larger than them, to a target – the demonstrator was an artificial insect (on a stick held by the experimenter) pushing the ball. The bumblebees quickly got the idea, but preferred pulling the ball while moving backwards over pushing it. These bumblebees were the demonstrators in the next phase.


In the main experiment, new, untrained bumblebees were divided into three groups. Each insect in the first group could watch another bumblebee dragging one of three available balls to a target and they both received a reward – a drop of sugar water. Insects in the second group saw a ball that moved “by itself” to the target (with help of a researcher-directed magnet under the platform). When the ball reached its destination, the watcher would get a reward. Insects in the third group simply found the ball already at the target with the reward next to it. Each demonstration/trial was conducted only three times.

Then the bumblebees were tested without further demonstration and only got a reward if they brought the ball to the target themselves. Virtually all bumblebees that had had a live demonstrator successfully dragged the ball to the target and did so faster than the other two groups. Those that had seen the ball moving by itself completed about 8 out of 10 trials. Finally, those bumblebees that had simply found the ball next to the reward were successful on average in only 3 or 4 of 10 trials and took the longest.

The student has become the master

Interestingly, the bumblebees did not simply copy what they observed early on. The bumblebee-demonstrator and magnet-using scientist always moved the farthest ball to the target. The student bumblebees usually moved the one closest to the target, even if it had a different colour than the one in the demonstration. And it was not a result of closest ball being pushed accidentally to the target, because the bumblebees usually dragged the ball actually being in-between the ball and the target.

To sum up: firstly, the bumblebees quickly learned a new task requiring the use of a tool (ball) and behaviour that has little to do with normal bumblebee foraging. And secondly, they did not blindly copy a previously observed behaviour, but used a more efficient method – moving the ball closest to the target.

Such unusual experiments show how great a capacity for learning and flexibility in problem solving these common insects have.

Do bats know the speed of sound from birth or do they have to learn it?

Kuhl’s pipistrelle bat

Most bats use echolocation to orient themselves in space. This means that they produce high-frequency sounds and can judge the distance of obstacles that reflected the sound based on the return time of the echo. However, to judge the distance based on the time the echo returns, one needs to know the speed of sound. The problem is that the speed of sound is not constant: it can vary in nature by more than 5% depending on temperature, humidity or altitude*.

What would be your guess: are bats born with the innate knowledge of the speed of sound and therefore distance judgment, or do they need to learn this?

Since the speed of sound is not constant, scientists predicted that knowledge about it is not innate in bats, but rather gained through experience. However, research on Kuhl’s pipistrelle bats (Pipistrellus kuhlii) has shown that the opposite is true.

These bats occur mainly in the Mediterranean region and in the West Asia. In their natural environment, they experience a wide range of temperatures and thus conditions with different speeds of sound.

To assess the effect of the speed of sound on bats’ echolocation and behavior, scientists conducted experiments in normal air and helium-enriched atmospheres – with a higher speed of sound and therefore a faster echo return time**. Young bats that were reared from birth in different conditions were compared to each other as well as to adult bats that had grown up in normal air.

It turned out that in the atmosphere with helium, bats, regardless of their age or rearing environment, assessed the distance to a target (feeding platform) as being closer than it actually was. Their echolocation pattern was the same as for closer objects in normal air. Additionally, in helium atmosphere, bats often slowed down and prepared for landing too early, thus landing ahead of their intended target. Even after several days in the helium atmosphere, the bats did not change their behavior and missed their target as often as at the beginning of the experiment.

This indicates that the speed of sound is encoded in the bats’ brains from birth, and the world seems to be perceived in terms of time rather than distance.

But how do bats deal with changes in the speed of sound in the wild? Firstly, these changes are usually smaller than those encountered in experiments. Secondly, as the bat approaches the prey or obstacle, the absolute error in distance judgement decreases. The error is a fraction of the distance – for example, if the speed of sound is increased by 10%, the object that is 100cm away seems to be 90cm away – error of 10 cm. But if the object is 10cm away the error is only 1cm. Lastly, bats usually don’t catch prey with their mouths, but entrap it with their wings and tail membrane, so they don’t have to be very precise. Although, even in the wild bats may miss their target.

While animals have amazing abilities to learn and adapt to their environment, in this case they seem to rely on innate skills even if they are not perfect in all conditions.

* For example, in standard air at 0°C, sound travels at about 332 m/s and at 30°C it travels at 350 m/s. So, the echo returns faster at higher temperatures.

** The experimental conditions increased the speed of sound by 10%, 15% or 27% – depending on the amount of helium.

Photo: Leonardoancillotto86 – Italy, CC BY 3.0,

Did you know that birds use cigarette butts to fight parasites?

Male house sparrow

Recently I took part in a cleaning action in my village. It was actually already rather clean, and we found little rubbish on the streets and sidewalks. However, about two out of three pieces of garbage were cigarette butts. This reminded me that some birds living in cities use those remains of smoked cigarettes to line their nests. Why do they do that?

More cigarettes – less parasites

Research conducted in Mexico City on house sparrows and house finches shows that there were fewer parasites in nests that contained more cigarette material. Adult birds and chicks are vulnerable to attacks by parasites such as ticks, mites and fleas, which not only suck blood but also spread disease.  The filters of smoked cigarettes are saturated with nicotine, which tobacco plants produce to fight small herbivores. Nicotine and other toxic substances in cigarettes repel or even kill parasites. Nests with more cigarette material had better hatching success and chick growth and survival rate.

Cigarette treatment

However, do the birds use butts specifically for their medicinal purposes, or simply for insulation, and their anti-parasitic effect is just a bonus? To test this, scientists replaced the original nest lining of house finches with an artificial one – either without parasites or with added live or dead ticks. The birds that got live ticks added more cigarette butts to their nest than birds from other groups. This show that birds use cigarette butts in response to parasites as a way of self-medication.

There is no such a thing as a free cigarette

However, we know that cigarettes are harmful to human health. They contain nicotine and other toxic substances. Are they not harmful to the birds? Unfortunately, it seems they are. Birds with more cigarette material in the nest have more DNA damage, which can lead to cancer (although a direct link between cigarette use and cancer in birds was not investigated). More DNA damage occurs in both the chicks and their parents – especially the ones that spend more time building the nest or incubating the eggs.

Adding cigarette butts to nests seems to be birds’ adaptation to city life – the use of human waste for self-medication. However, we still do not know if the short-term benefits outweigh the long-term costs. Therefore, smokers have no excuse to throw their cigarette butts on the street.

Photo: JrPol, CC BY-SA 4.0,

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Did you know that dolphins know when they do not know?

When I was younger, I watched “Who wants to be a millionaire?” on TV sometimes. You probably know this program or one like it, in which a participant has to choose a correct answer to a question from among a couple of options. When they choose the right answer, they can continue to play for an increasing prize, but when they are wrong, they lose most or all they have won so for. But there is also a third option – the participant can decide not to choose any of the answers, but to finish the game and take with them what they won so far. Of course, the last option only makes sense if the participant doesn’t know the answer to the question.

Many animals were tested in set-ups similar to “Who wants to be a millionaire?” and like humans, they more often chose to evade “answering” when the task was too difficult.

In one experiment, scientists trained a buttlenosed dolphin to press one button when it heard a high-pitched tone (2100 Hz) and another when the tone was lower (between 1200 and 2099 Hz). At the beginning the choice was easy – the sound was definitely low or high – but with time difficulty increased (with the lower sound getting closer to the border between high and low – 2099Hz).

When the dolphin pressed the appropriate button, he got a reward (praise and a fish). However, when he chose wrong, he got nothing and had to wait a while for a new sound and another chance. Then a new button was added between the original two. When the dolphin pressed it, he didn’t get a reward, but after a short delay, a new, easy trial began. However, when the dolphin chose this option too often, the delay increased.

What did the dolphin do? Initially, when the high and low sounds clearly differed from each other, the dolphin had no problem choosing the correct button. However, when the sound was harder to determine, he often showed signs of uncertainty – he moved more slowly to the buttons, hesitated between them, and it took him more time to decide. In addition, he chose the middle button more often – that is, he did not try to win the reward right away, but rather preferred to wait for the next attempt.

The scientists who conducted this study did the same experiment on humans (not under water, but at a computer). The human choices were practically the same as those of the dolphin. Most people said they chose the middle option when they weren’t sure if the sound they heard was low or high. Although the dolphins could not explain their choices, their behavior indicates that they may similarly evaluate their uncertainty and respond accordingly.

Similar experiments have shown that different species of monkeys, rats, pigeons, or even honey bees also avoid difficult choices, if possible. They seem to “know that they do not know”.

Photo: Pixabay

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Did you know that ants’ brains can grow or shrink depending on their role in the nest?

Indian jumping ant (Harpegnathos saltator)

Many species of ants live in colonies with fixed reproductive roles: one or more queens that lay the eggs, and many sterile workers who forage for food, care for the queen, her young offspring and the nest. In most species these roles are for life, but there’s some in which workers can assume the role of a queen.

One such species is the Indian jumping ant (Harpegnathos saltator). They live in small colonies of about 100 individuals. Colonies are started by a single queen. Most of her offspring becomes workers. When they are young, they work in the nest and their brain is relatively small. Older workers start to forage outside the nest and their brain grows – after all it is needed for spatial orientation, hunting and defence.

When the founding queen grows old, the workers fight to take over her place. The victorious ones turn into so-called gamergates. Their genes related to reproduction activate, hormonal changes occur, egg production begins, and aging slows down. Their behaviour also changes. Experiments have shown that when attacked, the gamergates do not defend themselves, but rather run away. And when they are left alone with a living prey, they do not attack it. Additionally, their brain shrinks (its size is approximately 20% smaller than that of foragers). The work of the brain requires a lot of energy, and since the gamergates are under the constant care of workers, it is better to use this energy to produce eggs than to maintain an expensive organ that is hardly used.

Recently, scientists have shown that all these changes in the gamergates are reversible. When they were separated from the nest for a few weeks and then returned to it, it appeared that they lost their reproductive status. Other ants began to police them so that they would not lay eggs. The former gamergates returned to the role of workers. They stopped producing eggs, spent most of their time outside the nest, began producing venom and started hunting and defending themselves from enemy attacks. Their brain grew back to the size of worker foragers.

Therefore, in this species the brain is very flexible. More so than the brain of bees and fruit flies.

Photo: L. Shyamal – Own work, CC BY-SA 4.0,

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Do you know how many different animal species live in the world?

Approximate species abundance of different groups of animals. The area of ​​each photo is proportional to the number of species in the group. A photo shows only one species from a given group – my subjective choice. Many other groups (with fewer than 5000 species) are not included here.

Today is the International Day for Biological Diversity. We know of around 1.5 million named and described species of animals in the world today. Scientists estimate that there may actually be between 3 and 30 million.

The animals that we most often pay attention to, such as mammals and birds, are only a small fraction of all living species. There are more species of gastropods (snails and slugs) alone than all vertebrates combined (mammals, birds, reptiles, amphibians and fish – see picture above).

Every year we discover new species of animals. But unfortunately, some species also disappear forever – mainly because of human activities, like destruction of natural habitats.

If you are interested in preserving nature’s richness for yourself and future generations, I suggest two easy ways to help maintain biodiversity (but there are many more).


Eat less meat.

Big areas of natural habitats, including tropical forests – which are the environments on land with the highest biodiversity – are constantly being destroyed in order to cultivate crops (such as soybeans) which are mainly used for livestock feed (also in Europe). 4 billion people could be fed by the crops that are now grown for (industrial) farm animals. The production of meat is a very inefficient process. At least 70% of the calories and proteins contained in plants are lost in the basic metabolism of animals and are not converted into calories or proteins in meat.


If you have a lawn, do not mow it very close to the ground, and mow it less often. This way, you will have more time to relax (which you could spend, for example, taking a closer look at the animals around you). You will save on fuel, and longer grass is more resistant to drought. And of course, this gives flowering plants a chance to bloom before being cut down. Their seeds are probably already in the ground waiting for their chance to grow. Flowers provide food for many insects, such as bees (around 2000 species live in Europe, from the larger bumblebees, to few-millimetre-long ones), butterflies (almost 500 species in Europe) and even flies and beetles.

If you want to have short-cut grass where you walk or chill, why not leave the longer grass under the trees or in a corner where nobody spends time? My neighbours mow half of their lawn quite short and leave the rest longer and only mow paths in it. I think it looks nice*.

Wild plants flowering now around my house.

I hope that today (and not only today) you will find a moment to look at the animals (and plants and fungi) around you – in the garden, park, forest or even on your balcony. If you want to know what species you see, you can use one of many phone applications available. I recently discovered ObsIdentify. Although I usually prefer to leave my phone in my pocket and just watch.

* If you have children running around the whole garden, better not to let grass grow too much (over 20-30 cm). Unfortunately, ticks like to sit on the taller blades.

Animal photos: Bob Goldstein, NOAA/Monterey Bay Aquarium Research Institute, Richard Ling, Hoi Maeng, Crisdip, Francesco Ungaro, Zhr16, Pixabay, Magdalena Kozielska-Reid

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