For parrotfish living in Australia’s Lizard Island coral reefs blood-sucking sea bugs can be a bother at night. These parasites called gnathiid isopods also prey on parrotfish during the day, but at this time other fish called cleaner fish remove the parasites from the parrotfish and eat them. It’s a good deal. Parrotfish are rid of parasites and cleaner fish get an easy meal.


Parrotfish, or Chlorurus sordidus, as they are known in the scientific world, help keep coral reefs healthy. Image by Julien Bidet for Seamarc/Wikimedia Commons.

At night, however, when parrotfish sleep, cleaner fish go off duty, but the blood-sucking parasites do not. Alexandra Grutter, a coral reef expert in Australia, tells me that she suspected that parrotfish had other ways to avoid being infected by isopods at night.

“Parrotfish sleep inside a cocoon of mucus. This looked like a way to avoid isopod bites, just like a mosquito net would protect us from bugs while we sleep,” Grutter said. I was intrigued. How would they test this idea?

Jennifer Rumney, a marine biologist working in the Grutter lab, took on the challenge of testing whether a cocoon of mucus in parrotfish would work like a mosquito net does in people. For Rumney, the experimental design meant tiptoeing in a completely dark room around sleeping parrotfish, dealing with blood-sucking isopods, and sleeping very little on her part.

“I began the experiment by placing parrotfish in individual containers in the lab,” Rumney explained. “At night, I turned the lab lights off and waited for the fish to make their cocoons and fall asleep.”

Each night, parrotfish make the mucus in an organ that is near their gills. The mucus exits through the gills and, in about an hour, surrounds the body of the fish. The next morning, the fish leaves the mucus envelope and goes about its daily activities. Next evening, when parrotfish go to sleep again, they make another cocoon.


A few hours after the fish had gone to sleep, Rumney quietly entered the room and checked on them. She did not want to wake up the fish. If they woke, they would exit the cocoon and Romney would not be able to do the experiment. So, she did not turn the lights on; she found her way around the dark room with a flash light that put out red light that did not wake up the fish.

Rumney checked that all the fish had made their cocoons. Then she gently pushed some of the fish out of their cocoons without waking them, and took the slippery cocoon out of the container. She left the rest of the fish inside their cocoons. Next, she added isopods to all the containers and left the room.

“Rumney went back to the room at regular times during the night to make sure the fish continued to sleep,” Grutter said. “The last visit was before the fish woke up. She then collected the parasites on the fish and also the parasites in the container. Rumney didn’t sleep very much.”

Rumney counted the number of isopods she had recovered from parrotfish, both with and without cocoons. She found that fish that spent the night without a cocoon had more parasites attached to their bodies than fish that had remained inside their cocoons. Also, the parasites Rumney recovered from the fish without a cocoon had more blood inside them than the parasites from the fish inside cocoons.

The scientists found that the mucus cocoon parrotfish make at night does indeed reduce the isopod’s attacks by working like a mosquito net does for people. It is possible that the cocoon may also play other roles, such as discouraging moray eel or other predators from eating the fish or maybe preventing fish scent from attracting predators. These other possible roles have yet to be tested in the lab. Here is a short video showing parrotfish inside a mucus cocoon.

Thank you for reading! Will you join me next time for more intriguing animal secrets?

Ana Maria

Ana Maria S. Rodriguez


Here is the reference for Alexandra Grutter’s original publication on this topic:

A.S. Grutter, et al., Fish mucous cocoons: the ‘mosquito nets’ of the sea, 2011, Biology Letters, Vol. 7, p. 292.

For more facts about parrotfish, visit this link.


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Mama brown bears have a big problem. During mating season, males can be very aggressive to cubs that are not theirs, killing about three of every ten cubs. Mama bears do what they can to protect their cubs. Sometimes they try to defend them, but males are larger and stronger than females. Males can grow about 8 feet tall (2.4 meters) and weigh about 700 pounds (320 Kg). Fortunately, after the mating season ends, cubs are no longer victims of male bear attacks.

Kodiak_brown_bears_FWS_18394 smaller

Mama bear with her cub. Courtesy Lisa Hupp/US Fish & Wildlife Service

This situation did not seat well with mama bears (no kidding!), and I was intrigued (and happy!) when Sam Steyaert, a brown bear scientist in the Scandinavian Brown Bear Research Project in Tackåsen, Sweden, told me that mama bears had come up with a strategy to keep their cubs out of danger from male bear attacks. I had to hear about it!

Steyaert and his colleagues keep track of brown bears’ whereabouts in Tackåsen with GPS tags on collars attached to the bears. Every morning, Steyaert grabs a cup of coffee and sits at his desk in front of a computer. He clicks a button, leans back on his chair and sips his coffee while the GPS data from the night before downloads into his computer.

“The software plots on a map series of dots that represent the locations of a bear throughout the night, and connects the dots,” Steyaert said. “It does this for each bear we are tracking, which includes males and females.”

Steyaert can now see which bears crossed paths and which stayed apart.

“During summer and fall, male and female bears cross paths often. They remain in the same area to feed, getting ready for winter,” Said Stayeart. “But when I looked at the data from spring and early summer, the mating season, I found something quite different.”

Steyaert saw that from early May to mid-July, some mama bears with cubs do not cross paths with males. These females and cubs do not eat, sleep or travel in the same areas male bears roam, even if those areas have abundant food. This pattern repeats every season. Steyaert thought that mama bears had found a way to protect their cubs by staying away from the males during the time they were aggressive toward cubs. Now, to prove it, Steyaert joined forces with Boss.

Steyaert and Boss, crime scene investigators

The GPS data showed that some mama bears and their cubs moved to an area male bears did not travel to, but also that other mama bears with cubs did remain where males lived. Steyaert’s plan was to compare both groups of mama bears with cups regarding cub survival. Would cubs that stayed away from males survived more often than those that crossed paths with males?

Every morning, Steyaert studied the GPS data collected the night before, identifying mama bears that had crossed paths with males. Then, he went out into the forest to see with his own eyes what had happened when males, females, and cubs came close to each other.

Steyaert went to the forest with Boss, his bear-tracking dog. Boss is a Jämthund, a type of dog typically trained for moose and bear hunting. Boss looks a lot like a wolf with a curly tail. He helps Steyaert find bear tracks, scat, and sometimes bears that are dead or alive.

When Boss and Steyaert found an area where males and females had crossed paths, they tried to figure out what had happened. Had there been a fight? What had happened to the cubs?

After analyzing many crime scenes, Steyaert confirmed his initial suspicion. Mama bears that stayed away from males kept more cubs alive than mama bears that had encountered males. But, bears can travel long distances. They could have easily followed females that wanted to stay away from them. Why didn’t the males follow the females?

The answer was in the GPS data plotted on maps. Mama bears that stayed away from males had chosen areas of the forest that were close to people’s homes. These areas, however, were not so close that people would become concerned about having brown bears almost in their backyard. Males, on the other hand, try to stay as far away from people as possible. For male bears, man is the top predator.

I was fascinated by these findings. Mama bears had modified their behavior in a way that gave their cubs a better chance of surviving male bear attacks by using a ‘human shield.’

Thank you for reading. I am looking forward to preparing another science true-story for you next time!

Ana María

Ana María S. Rodríguez


Interested in Sam Steyaert’s original science paper about this work? Here is the reference:

S.M.J.G. Steyaert, et. al., Human shields mediate sexual conflict in a top predator,” 2016, Proceedings of the Royal Society B, 283 (online publication).

Here you can find more information about brown bears.


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People can understand animal emotions. But can animals understand ours? Young scientist Amy Smith suspected that this was possible, especially with horses.

512px-Chestnut_horse_head,_all_excited Wikimedia commons

This chestnut horse watches at the camera with great interest. Wikimedia Commons

Smith grew up in a house with lots of pets. During the summer months, she stayed at a farm in Southern Ireland where she became very familiar with horses. As many of us know, animals are very good at communicating how they feel. For instance, an angry dog will bare its teeth, and a happy one will wag its tale and nuzzle your arm.

People often say that horses are good at reading people’s emotions. This is a reason they are good therapy partners of people who struggle with their physical and mental health.

“Horses also can sense the emotions of their herd mates,” Smith told me in an interview. “As a student of animal behavior, I wanted to objectively study whether horses were capable of understanding what people were feeling.”

Before conducting her study, Smith searched the scientific literature for works similar to the one she was planning. Although she found work with dogs that showed that they do respond to human emotion, she did not find much scientific work on this topic about horses.

Bring on the video cameras!

In the early morning hours when it was still dark, Smith and her colleagues walked toward the stables in a farm in Sussex, U.K. carrying several video cameras, tripods, and large photographs of men with angry or happy faces.

“People we encountered gave us a funny look,” Smith said. “They didn’t know that we were about to begin our experiments. We set up our equipment in an empty stable and brought one horse at a time.”

Smith and her team showed each horse a large picture of a man’s face and video recorded the horse’s reaction. First, they showed the horse a happy face, and in a second group of tests, an angry face. In addition, they measured the horses heart rate. After video recording the sessions with the horses, Smith and her colleagues returned to their lab to study the videos and the heart rate measurements.

To make fair observations of the horses’ responses to the photos, the scientists conducted ‘blind’ analyses, meaning that, when they studied the videos, they did not know whether the horse was seeing a happy or an angry face. Then, they compared their individual analyses of the videos and were pleased to see that they had independently recorded the same results.

They found that horses turned their head to the right and gazed at the picture with their left eye when they were looking at an angry face. However, they did not seem to move their heads when they faced a happy face. The heart rate supported the video recordings; it increased more when the horse was looking at an angry face than when facing a happy face.

Makes you wonder. If horses can read happy and angry faces, maybe they also can understand other emotions. And maybe other animals, not only dogs and horses, can sense how people feel by looking at their faces.

Thank you for reading. Will you join me again next time?


Ana Maria S. Rodriguez


If you are interested, here is the reference to Amy Smith’s original work:

Amy V. Smith et al., Functionally relevant responses to human facial expressions of emotions in the domestic horse (Equus caballus), Biology Letters, 2016, Vol. 12 (online publication).


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The countdown to Earth Day 2019 continues and today we will travel to the Kalahari Desert to visit a meerkat school where passing the final test is a matter of life and death.


Adult and young meerkats keep close watch on their surroundings. Wikimedia Commons.

About the size of a small cat, meerkats are highly social mammals that live in the Kalahari Desert in southern Africa in groups of up to 40 individuals. They burrow their dwellings, keep watch on their surroundings by standing still on their hind legs like a guard on watch, and teach their young survival skills.

Alex Thornton studies meerkats and he told me about what could be ‘a day in the life of a meerkat pup’ story he observed during one of his trips to the Kalahari.

“A hungry meerkat pup blurted out begging calls. An adult meerkat responded by bringing the pup a dead scorpion that was bigger than the pup’s head! The pup did not hesitate. It took the scorpion in its mouth and munched on it slowly.

Suddenly, a large bird called a yellow-billed hornbill saw the pup eating the scorpion and got closer to it. The hornbill yanked the scorpion, but the pup did not let go. The bird took flight, lifting the scorpion and the meerkat with it. The hornbill lunged and plunged, but the pup held on. Finally, five feet (1.5 meters) above the ground, the pup let go of the scorpion and hit the desert floor unharmed.”

Life is not easy for a meerkat pup!

Meerkats are omnivores, they eat plants and other animals. One of their favorite foods is scorpions. Some scorpions have enough venom to kill an adult person; nevertheless, meerkats do not seem to be discouraged by the prospect that each scorpion they catch might be their last.

How do meerkats manage to feed on such a deadly feast? Thornton and his colleagues observed this intriguing meerkat behavior patiently for years and found a fascinating answer.

“Pups are initially incapable of finding their own prey,” Thornton said.

Pups make loud begging calls, but the adults do not reply by feeding the pups. They respond by ‘enrolling them’ in a two-month survival program that includes three main lessons:

Lesson #1: How to eat a dead scorpion.

This lesson provides four-week-old pups with their first encounter with a scorpion. A hungry pup raises a racket of begging calls. In response, an adult kills a scorpion and brings it to the pup. The more they practice this lesson, the better the pups get at handling and eating dead scorpions. The pups change their calls, which is a clue for adults to move on to lesson 2.

Lesson #2: How to eat a live, stingless scorpion.

In this lesson, an adult catches a scorpion, bites off the poisonous stinger and gives the live, stingless scorpion to the pup. If the scorpion tries to escape, the adult catches it and brings it back to the pup. This practice continues until pups are about 90 days old, when they seem to be ready for the final lesson.

Lesson #3: How to eat a live scorpion with a stinger.

An adult catches a scorpion and brings it alive, stinger and all, to the pup. After observing hundreds of meerkats go through survival school, Thornton and his colleagues concluded that the more the pups practice lessons 1 and 2, the better their chances will be of doing well in lesson 3.

Scientists know that some young animals learn from older animals of their own kind. What is hard to tell is whether the adult is teaching the young or the young is learning by imitating the adult. In this case, Thornton and colleagues’ work showed that meerkats do teach their young how to handle deadly scorpions. Meerkats are the first mammals, other than humans, known to teach their young. Some ants and birds called pied babblers also teach skills to their kin. More on this in a reference below that includes a video.

Thank you for reading! I am looking forward to your next visit.

Ana Maria

Ana Maria S. Rodriguez


For those interested, here is Alex Thorntons’ reference to his original work:

Thornton, A, and McAuliffe, K. Teaching in wild meerkats, 2006, Science, 113: 227.


This reference is about other animals that teach and includes a video of meerkats handling another one of their favorite foods, giant, poisonous millipedes!


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Paving the road toward celebrating Earth Day on April 22, I’ll be posting about some of Earth’s fascinating creatures and their ‘WOW!” adaptations to surviving in the world. Let’s begin with the electric eel.


The electric eel has many uses for its electrical power. Wikimedia Commons

Unless you live in the country side of South American nations such as Brazil, Suriname, Venezuela, Colombia, Ecuador, or Peru, and like to roam on slow-moving bodies of water of the Amazon and Orinoco Rivers, you are not in immediate danger of being shocked by an electric eel. (Of course, zoo keepers of this eel, beware)

Nevertheless, this intriguing fish may spark your attention because, unlike other fish, electric eels need to surface to breathe air. They can grow to be as long as an 8-foot man is tall and they can discharge about 600 volts. This is five times the discharge of one electric socket in US households, and about 3 times the power in electric sockets in other countries’ homes.

Scientists have been fascinated by the eels’ ability to manipulate electricity to aid its survival. And some scientists let their curiosity make them do truly weird experiments.

The eel scientist

Meet Ken Catania. He studies strange-looking creatures, such as the star-nosed mole and its unusual way to smell its underwater environment (more on that in a future post). More recently, Catania has been focusing on electric eels, and their ‘shocking’ abilities.

He discovered that eels can control how much electricity they put out. They use low voltage pulses to sense for prey, and they can turn up the power to make prey (think of fish) twitch and reveal its hiding location. An eel also can discharge a stream of high-voltage pulses to paralyze prey and easily suck it into its mouth in a flash. Fascinating!

But then, one day Catania was standing by the electric eels aquarium in his lab holding a net in his hand. He was going to use the net, which had a metallic rim and handle, to transfer eels from one tank to another.

As he submerged the net in the water, some of the eels swam away from it, but others zoomed toward it. In an instant, an eel leapt up and climbed along the net’s handle, firing a racket of high voltage pulses. Then, it dropped into the water. Catania was not hurt by the electric shocks because he was wearing insulating gloves, but he was very ‘shocked’ by what had just happened.

“Under no other circumstances were eels observed to leap out of the water,” he said.

Of old tales and leaping eels

Just when scientists thought they knew all there was to know about electric eels, here comes a serendipitous observation that makes them wonder. Why would eels jump out of the water? Catania had to solve the mystery.

He began by researching the scientific literature and came across an odd South American story from famous explorer Alexander von Humboldt. Humboldt wrote of eels jumping out of the water, attacking a group of horses that had stepped into a pool where the eels lived.

“The aggressive behavior of the eels, taking the offensive against the horses, seemed the most fantastic and questionable part of the story,” Catania said.

But he had observed the jumping behavior with his own eyes, so he decided to test it in the lab and measure the eels’ electric output when (if) they jumped. What advantage would the eels gain by jumping out of the water?

Catania knew that when eels swim emitting electrical discharges, an electric field forms around them. If a predator on the surface reaches toward an eel through the water, it won’t feel much of an electric charge. Would this be different if the eel jumped out of the water? And here comes the seemingly weird, but very illustrative design part of his experiments.

Catania used props shaped like alligator heads and human arms that were equipped with electric sensors that lit up when electricity flowed through them. He also carried out experiments using his own arm shielded by an insulating glove. With these tools he tested his eels’ ability to jump as Humboldt’s eels allegedly did, and measured their electric power.

The eels did not disappoint. These eels can jump! As they rose above the water touching the props, they discharged enough electric power to lit the sensors. That power, Catania estimated, also would be enough to cause intense pain in an predator trying to catch the eel. Discouraged and in pain, the predator would leave the eels alone and most likely will remember the experience next time it comes across a pond.

About two hundred years after Humboldt told the story of the jumping eels, Kenneth Catania not only confirmed his observations, but also revealed another amazing adaptation of the most powerful electric fish.

I invite you to see this short video showing some of Catania’s experiments and an 1800’s illustration of Humboldt’s story.

Thank you for reading and I hope you visit again!

Ana Maria

Ana Maria S. Rodriguez

Interested in reading the original sources describing Catania’s work?

  1. Catania, K. Leaping eels electrify threats, supporting Humboldt’s account of a battle with horses, PNAS,
  2. Catania, K. The shocking predatory strike of the electric eel, Science, 2014, Vol. 346, Issue 6214, pp. 1231-1234. (This link only provides an abstract of the work. Request the complete article via your public library).

More information about eels:

The Electric Eel, Smithsonian’s National Zoo & Conservation Biology.


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What a day it was! Ms. Mitchell was right; I was exhausted at the end on my author visit, but all of it was worth it.

Humble ISD Elementary School second, third and fourth grade students dove with me into the deepest oceans to uncover the secrets of deep diving mammals. After that, we traveled to African deserts tagging along with scientists who worked with live-sized toy lions to reveal what the lion’s mane is for.

4 smaller Humble Elementaty April 20, 2018

The students were an amazing audience; attentive, curious, and they asked so many questions that I barely had the time to answer them all.

Thank you all for a wonderful experience!

“Teachers and students learned a lot and are excited to read your books; we already have a check-out waiting list!” Ms. Mitchell said later on an email.

What else can I ask for? Happy reading!


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On January 5th, Archimedes Notebook  posted a wonderful review of The Secret of the Scuba Diving Spider. Unfortunately, life got in the way and I did not see it until today.

Spider low res 9780766086296

I felt a mixture of cheer and sadness; I loved the review, but was sad that it took me so long to see it. I immediately sent an email to Sue Heavenrich, thanking her for all the great comments she had about my book. Sue, I do appreciate the time you took to review it.

And then I learned that Sue had also posted her review in STEM Friday. A bonus for The Scuba Diving Spider, which is in the company of another book also reviewed in the same post, How Many Hugs? written by Heather Swain and illustrated by Steven Henry. You would be well served checking that one out, too.

STEM Friday

I hope you take a few minutes off your day to read the review Sue wrote. If you find the book useful to teach either at school or at home, you may also find useful the accompanying teacher’s guide.


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