Critters That Glow In The Dark

Luminescent (top) & Fluorescent animals

In Part IV of our All About Color series (June 28, 2020), we discussed the signals exchanged between male fireflies and their female glowworms, and talked about sea creatures that generate their own light (bioluminescence); additionally, we examined some organisms (like scorpions) that show surprising colors under ultraviolet light (fluorescence).  These are areas of study in which exciting things are happening right now and we would like to point out some of the more interesting discoveries.  Some of them have been discovered since that article appeared. (Underlined items link to recent articles.)

For a long time, it was believed that the vast majority of bioluminescent sea creatures spent part or all of their lives in the deepest, darkest parts of the warmer oceans, although some (jellyfish, comb jellies, and some squid) rose to the surface at night before daylight drove them back to the depths during the day.

Lanternfish

As better and better deep sea exploration is done, scientists are seeing more and more sea creatures that glow, either to lure prey into their mouths or to escape predators. Better cameras that can withstand the greater pressures at greater depths showed them some surprising animals glowing right along, in some previously unknown places. For instance, only recently bioluminescent species were found near the sea floor of even the coldest arctic waters.

Newer, stranger, and larger animals have been found.  For example, some squid shoot out a glowing liquid instead of the usual ink in order to confuse predators while the squid escape.  There is at least one squid that changes the color of its luminescence to match moonlight  and sunlight. Translucent skin allows a high level of transmission of light, especially in the blue-green color range. At least three species of sharks found off of the coast of New Zealand are known to light up their undersides with a blue-green glow, which makes them difficult to see. These are not the tiny bottom-feeding sharks, either. They are at least six feet long and inhabit the area of the sea from a depth of 200 meters to one of 2000 meters (650’ to 6500’). This range is sometimes called the Twilight Zone and isn’t as dark as the lightless regions previous known species inhabit. As late as 2020 these sharks were believed to be the largest living vertebrates  capable of luminescence.

 

Bioluminescent shark

But, wait a minute, what about whale sharks?  Whale sharks are huge fish that have skeletons of cartilage instead of bone.  They are filter feeders that swim through the water with their huge mouths open, scooping up plankton, fish eggs, and small fish.  Well, they aren’t bioluminescent; but they ARE fluorescent! It turns out that they have blue dots on their backs that glow green when they are in relatively shallow water. The current theory is that they use the dot patterns to communicate with each other so that they can school together in large groups, either for hunting prey or mating. More work needs to be done on this phenomenon.

Whale shark

Now it is generally conceded that approximately 3/4 of marine life glows to some degree or other, but we are far from understanding all the ways they accomplish this.  Now if we only we had a glowing whale….

When an animal is bio-fluorescent, it is usually because it has taken in a short wavelength of ultraviolet (UV) light and then re-emits it as a longer wavelength of a color from the visible spectrum. There are other ways to do this, but we do not yet really understand them.

Fluorescent coral

Scientists have known for a long time that animals that find food and/or shelter on coral reefs adopt colors or patterns that make them hard to see among the coral occupants (camouflage). However, these creatures themselves can see light wavelengths that we — and the predatory fish that might feed on them — cannot see. This property is known as bio-fluorescence, and does seem to extend to wavelengths longer than just UV.  Most of these animals are relatively small — a few inches long at best. For example, some crustaceans send our light signals when it is mating time. But as scientists began to study such animals, they found larger and larger specimens.

Not so long ago, a supposedly scholarly paper announced that there were no bioluminescent or bio-fluorescent non-flowering plants, amphibians,    reptiles, birds, or mammals. Wrong on all counts.  The amphibians may take the blue ribbon. Of 32 species of frogs, toads, and salamanders studied in 2020, all 32 showed some ability to glow. In 2017 a fluorescent glow-in-the-dark frog was discovered in Argentina. This polka dot tree frog produces a blue-green pigment that has been determined to be bile produced by its bile ducts. It is not yet known whether the dots serve a specific function, are non-functional, or are structural colors made by layers of clear materials.  We discussed structural color in a previous post. 

 

Chameleon & Gecko

Reptiles are just beginning to be studied for bio-fluorescence.  So far chameleons and geckos have been found to glow in the dark. Some have such translucent skin that even their bones are seen to glow.  In 2016 researchers looking for fluorescent corals came across a fluorescent sea turtle.  Bear in mind that the ancestors of these animals lived as long ago as the dinosaurs. It might tell us something if dinosaur fossil bones and teeth are studied to see if they had any glowing properties.  And yes, such properties can sometimes be detected in very old specimens — especially if they were buried soon after death.

Puffins in mating colors

 

Birds may be the hardest to study because they are difficult to track in flight, but we know parakeets, eagles, herons, owls, puffins, and some penguins are already on the list. Some of these birds are nocturnal hunters.  Others migrate long distances and rest overnight on land or water.  The ability to glow could break up their silhouettes and confuse nighttime hunters. Some, like the puffins, have showy beaks during the mating season and these have glowing parts. Fluorescent bird feathers would likely be significant in mating rituals.

Springhare

There are already a number of placental mammals on the list and more being found all the time.  The numbers indicate that they may be much more widespread than we thought.  I wish that I had known that there were three species of flying squirrels (two of these have undersides that glow pink under black light) here in the U.S. long ago when my sister-in-law was raising them. So far my favorite glow-in the-dark mammal is the Springhare, a sweet little animal from Africa, very rare — only 2 species are known.  It looks like it has a short-eared bunny head on the body of a tiny pouch-less kangaroo. 

 

Echidna

The most recent shock was that not only was an unusual animal capable of glowing, but that it may have been doing so for an EXTREMELY long time!The animal is the platypus, an almost-mammal belonging with the echidna in a group called  monotremes.  These animals are members of an ancient group that have warm blood and fur, but lay eggs.  Once the babies hatch, a milk-like substance oozes from the parent's body to feed the young.  The echidna has a body which is covered with sharp spikes. Examination with an ultra-violet detector shows that when the animal crouches down on its nest those spikes glow a bright white. Not something a predator is likely to put in its mouth!

Next in line come the marsupials whose newborn, while in a very tiny, "unfinished" state,  has to crawl up the mother's fur to her pouch and fasten itself to a nipple.  Eventually it begins to spend some time outside the pouch, but still returns to it for some months. It had been known for years that the pouched American opossum could glow, but no one cared to investigate further. So it should not have been such a shock to find that the wombat, the bush-tailed possum, the koala, and the bandicoot could glow. Now we can tentatively add the Tasmanian Devil.  Museum specimens may be able to tell us about the extinct Tasmanian Wolf and Tiger.

Bandicoot & Tasmanian Devil

There is enough work here to keep both professionals and amateur scientists busy for years.  Yes, you read that correctly. While the search for new bio-luminescent creatures is usually the province of of professionals requiring cutting edge technology, bio-fluorescence needs much simpler and relatively inexpensive equipment and training to find — it seems that until recently, it just hadn’t occurred to anybody to take a serious look at the phenomenon! (And if there isn't a company out there making UV flashlights 24 hours a day, they are missing a trick!  This is fun everyone can get in on!)

 This post by Annake's Garden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Midsummer Madness: Celebrating the Summer Solstice Around the World

Each year around the 21st of June, we in the Northern Hemisphere celebrate the Summer Solstice — the longest day and shortest night of the year.  This has been done for centuries, and over that time many interesting ways have developed to mark the occasion.  As we did with the posts about Equinoxes, we have made some games and suggested activities you may want to use to celebrate.  The quiz games are a little harder this time, so you may want to have a world map or atlas at hand.
 
But first, with some help from NASA, let's see what causes the Summer Solstice.

The word solstice is made up of two Latin words, Sol, which means Sun, and Sististere, which means to stand still. So the sun appears to stand still at the solstice.  This happens at the same time all over the world. In the Northern Hemisphere, it rarely happens on the 20th of June, although this does occur occasionally. It is even rarer to have the Solstice happen on the 22nd. The next one of those will not happen until the year 2203.  (No need to mark your calendar.) While the Northern Hemisphere celebrates the Summer Solstice, at exactly the same time the Southern Hemisphere is celebrating the Winter Solstice — the shortest day and longest night of the year.

When the Sun appears to stand still, it does so over the Tropic of Cancer. Obviously since the sun appears to begin its journey at the Equator, it will take some time for it to reach the Tropic of Cancer.  If you live in the continental U. S., it is fairly easy to get the exact time when it gets there with a quick search online.  After a short hesitation, the Sun appears to reverse its course and head for the Equator once more.  I say "appears" because the Sun is not doing all this moving. It just looks that way.  It is the Earth that is moving, tilted on its axis.  As you can see in the diagram,  the north end of the Earth's axis is tilted at approximately 23.4 degrees. As it turns on its axis, it follows an elliptical orbit, not an even,  circular one.

Here is a game for you,  a matching game. The correct answers and some comments can be found at the end of this article.  Don't peek.  Try to match the way a group celebrates the Summer Solstice with the country where the celebration takes place. You can do this by drawing lines between each pair or by matching each number with the letter of the answer. You may want a map or globe to find some of the less well-known countries. (Remember, all of these are north of the Equator!) The numbers describe the celebrations. If you click on the caption under the quiz, it will open a PDF file that you can download and print.

To open PDF, click here.

Here is something that you might do with children. It is something that would be appropriate during the pandemic. On Mayday our teachers cut large circles of colored posterboard into quarters.  We rolled the quarters to make cone shapes and stapled them. We added little handles of the posterboard or punched two holes in opposite sides and made ribbon or yarn handles. Then we filled our cones with a few flowers. The idea was to hang the  'cornucopia' on the door-handle of an elderly or handicapped person, knock or ring the doorbell, and run away before they could see who did the good deed.  There would be even more flowers available in June.

Here is your second quiz game. This one is True or False.

1)  The Summer Solstice marks the first day of summer in many countries.
2)  The day after the Solstice, the days begin to get shorter.
3)  In Australia the people go sunbathing at the beach at Christmas.
4)  The sun hesitates at the Tropic of Cancer then heads for the Arctic Circle.
5)  When it is summer in the Northern Hemisphere, the Northern Hemisphere is closest to the sun.
6)  The Earth moves in an ellipse around the sun, not a circle.
7)  As the Earth makes the turn around the sun to complete its circuit, the axis turns so it is pointing in the opposite direction.
8)  When the Southern Hemisphere is at its Summer Solstice. it is closer to the sun than the Northern Hemisphere was at its Summer Solstice.
9)  The Winter Solstice in the Northern Hemisphere is on December 21.
10)  The hottest day of the year usually comes several weeks after the Solstice.

It has been my experience that when several generations get together, young children are often left on their own to play, which may result in minor injuries, hurt feelings, and outright fights.  This is an excellent time to take children four or older on a nature hike, supervised by at least two responsible older teens or adults of any age.  Each child should have a small bag that can hang over one arm and be tied shut before the trip back to the house. The trip can be as simple as one through a big backyard or neighborhood park or as complex as a trip to a seashore, desert area, forest, etc. The longer the trip, the more advance preparation (including first aid).   Later, after the explorers have been fed and rested, they can be given a lesson on pressing leaves and flowers and shown ways to display interesting rocks or other treasures.  If pictures have been taken during the trip, it would be nice to later see that each child gets a picture of himself or herself taken on the trip.  It is never too soon to encourage an interest in nature and science.

Here are some other quick ideas for celebrating the solstice:

• Fly kites.
• Have a scavenger hunt.
• Provide simple treats for children like popsicles, s'mores, ice cream sandwiches.
• Hold a recipe exchange (which doesn't have to be just for the ladies).
• Hang a nice backdrop and take all sorts of pictures, serious or silly.
• Plan pizzas with loads of seasonal toppers, including fruit.
• Watch an old movie together.
• Gather around the piano for a sing-along — or do it a capella. 
• Surprise someone with a phone call.
• Plan a block party and encourage everyone to make the whole circuit.

Maypole Dance

Here are the answers to the matching quiz.
    1) K ;  2) L;  3) P;  4) A;  5) N;  6) R*;  7) M;  8) Q;  9) C; 10) H; 11) D; 12) F;  13) J;  14) O;  15) E;  16) B;  17) G;  18) I**

*This could also apply to Switzerland, who fought off an attempted invasion by Napoleon using this tactic, but Austria was forbidden to light bonfires during the time of the Nazi occupation, and they have begun the practice again, so I gave them the credit.
**This year, due to the pandemic, the entire 3-day festival will be broadcast online, complete with a pow-wow, marketplace, lots of singing, dancing, beautiful native costumes. See it here.

Here are the answers to the True and False quiz.

Numbers 1, 2, 3, 6, 8*, 9, and 10 are True.
4 is False because it appears to turn around and head back down to the Equator.
5 is False because the earth is farthest from the sun at that time. And it is a good thing that it is, especially with temperatures on the planet continuing to rise.
7 is False because the earth's axis always points in the same direction.
8* is True and helps to explain the severe droughts and terrible wildfires that have happened for several years in countries like Australia and South Africa.

We hope you have had some fun with our Midsummer Madness. Look for a similar issue on the Autumn Equinox in September.  Stay safe.

 

This post by Annake's Garden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.