Isegoria

After doing some content analyses, Morgan Worthy (I Have Known the Eyes Already) asked 100 ornithologists to make blind ratings of large families of birds on “quick-versus-deliberate” behavior related to flight, feeding, and escape:

Twenty-one agreed to do so. Some left out those families with which they were not very familiar.

I included in the analysis all large families of birds for which at least 15 ornithologists had made ratings. When size was partialed out, the eye-darkness measure and the combined behavioral measures correlated .56 [d.f. = 33, p < .001]. As you probably know, John, that means that differences in eye-darkness, even using a two-point scale, accounted for about 31% of the rated differences in quick-versus-deliberate behavior. That is not trivial. The family of birds that was rated most deliberate was herons; the family of birds that was rated quickest was swifts. Whereas the reaction time differences with humans were small in absolute terms, in this study of birds, the behavioral differences were large.

If you are out in the yard with your pet, Morgan Worthy explains (in I Have Known the Eyes Already), and it sees a squirrel nearby, what it does next will probably depend on whether your pet is a cat or a dog:

The immediate response of a cat is to freeze, then crouch and start to stalk in preparation for an ambush. The immediate response of most dogs is to run, without delay, toward the squirrel and chase it. One is a stalker; the other is a chaser and uses immediate, direct pursuit. The first responses of cats and most dogs on sighting prey are very different from each other. Only after the prey has come close to the waiting cat or the cat has slowly worked its way close to the prey, does the cat suddenly pounce.

The typical dog makes quick moves; the cat makes sudden moves. Understanding the difference between those two words, quick and sudden, is necessary to understand everything else we will talk about. Quick implies an immediate reaction; sudden implies an abrupt move after some delay. The origins of the two words make this plain. “Quick” means “swift, lively.” “Sudden” means literally “to approach secretly” and comes from two Latin words that mean “secretly” and “to go.” One way to remember it is immediate quick and delayed sudden.

Another way to state this is that one is quick and the other is deliberate. If we can agree that most dogs tend to be quick and most cats tend to be deliberate, we can then move on to differences in eye darkness between the two. The reactivity hypothesis is that dark eyes are associated with quick responses and light eyes are associated with deliberate responses. Using our example, we can predict that dogs are darker-eyed than cats. A simple way to get a measure of eye darkness is to say that only brown eyes and black eyes are considered dark and all others are considered light.

[…]

Dogs tend to be significantly darker-eyed than cats. Of the 27 breeds of domestic cat, none are dark-eyed. They are all in the range of yellow-amber-orange-blue-green. None are at the other end of the scale—black, dark brown, brown—that we are treating as dark-eyed. The same is true for cats in the wild. Look with me here at the database (Worthy 2000, p44). In the wildlife literature we found eye colors for 15 species of cat. All had yellow or yellowish eyes except for one, the Ocelot, and its eyes are reddish brown. So, for 27 breeds of domestic cat and 15 species of cats in the wild, using our 2-point scale of eye darkness, every one of them gets a score of 0.

[…]

Most dogs react to prey by immediately giving chase. One group of dogs, though, employ an initial response to prey that is very much like the initial response of cats. Pointers and setters, like cats, freeze when they first sense prey nearby. Pointers adopt a standing pose and setters crouch. In regards to this initial response, I think any fair observer would grant that pointers and setters are more deliberate or cat-like than are other dogs. If the reactivity hypothesis is correct, those breeds (all are often just referred to as Pointers) should be less likely than other breeds to have dark eyes. That is, indeed, the case. Whereas 70% of other breeds are dark-eyed, only 28% of the pointer or setter breeds are dark-eyed. A difference that large, given the sample sizes, could occur by chance less than one time in a thousand.

[…]

Pointers are bred for “freezing” as first response to prey; hounds are bred to track and chase prey; terriers are bred for not only chasing the prey, but for following it into burrow or den—which requires a high level of persistence and courage. Simon & Shuster’s Guide to Dogs (Pugnetti 1980) uses a symbol to indicate adaptation for each of those three behaviors.

There is a progression. Fifty-five per cent of pointer breeds have yellowish eyes; for hounds, it is only 10%, and there is no breed of terrier that has yellowish eyes. Yellow eyes seem to be associated with hesitation or freezing behavior, which is good for animals that stalk. Hesitation would tend to be a liability for animals that hunt by means of direct pursuit. And that would be especially true for terriers, which are expected to pursue the prey into its den.

[…]

Dark-eyed animals show active courage; light-eyed animals that freeze when predators are near show passive courage.

One of the main things to remember, though, from our talking about cats and dogs, is that predators that depend a lot on freezing, ambush, lying-in-wait, stalking, or any other form of surprise to take prey will not only be light-eyed, but most likely will have yellowish eyes. I know we have only covered three examples so far—domestic cats, cats in the wild, and dogs that point or set—but the same pattern is seen with all classes of land vertebrates. Any type predator that uses surprise to ambush prey (in less than total darkness) tends to have yellowish eyes. That can be noted by anyone who cares to look within various orders or sub-orders of animals: frogs, snakes, lizards, crocodilians, carnivores, primates, raptors, owls, heron-like birds, and various other orders of birds.

No one can deny that statement, but they can ignore it. Given human history, people of good will are now reluctant to acknowledge any evidence that pigmentation can be related to behavior. We seem always to go from one extreme to the other.

[…]

Helen Mahut (1958) did a study in Canada in which she compared ten breeds of dog on response to novel stimuli and categorized the behavior as “fearless” or “fearful,” depending on how bold or inhibited the dogs were in their responses. I no longer remember the particular breeds, but when I checked the eye colors, the most fearless dogs were also the ones with the darkest eyes.

[…]

Asdell (1966) described wolves as being cautious, cowardly and fearful of novel stimuli. They pursue prey in a circling or zigzag manner in order to set up an ambush. That is not direct pursuit as is seen in terriers or weasels. Nor is it as non-reactive as the behavior of cats and pointers. Because wolves are lighter eyed than most dogs it is significant that Asdell also reported that wolf-dog hybrids exhibit “passive defense reactions” more than do most dogs.

Morgan Worthy, in the opening to his memoir, I Have Known the Eyes Already, explains his hypothesis about eye-color:

One day, probably in early 1971, I was looking through a magazine dealing with (American) professional football. I noticed, once again, that there were many African-American players who had made it to this advanced level of skill and that they were not evenly distributed across all positions. As I neared the end of the magazine, I had the strange, vague, feeling of being reminded of some remote association. I had lingered on this page looking at a photograph of a white player with very light eyes. Then I had my aha moment: earlier in looking at the magazine I had stopped to look at another photograph of a white player with very light eyes, and in both cases the player was a quarterback. Now I recognized, consciously, what had unconsciously caused the vague feeling of remote association. Of course, it might have been a coincidence not worth remembering at all, but then again, I had learned, in military intelligence, to pay attention to even minimal bits of matching information.

Almost at once, I began to wonder if white players at different positions had different levels of average eye darkness and, if so, whether this rank order of positions was positively correlated to the rank order of positions based on percentage of African-Americans playing the position. When I later tested my speculations, the answer was “yes”, on both counts. The two rank orders were positively and significantly correlated and both had quarterbacks at one extreme, with defensive backs at the other.

Defensive backs (especially those playing man-to-man) are much more dependent on immediate, quick reactions than are quarterbacks, who depend more on delayed, sudden reactions. Having already been thinking about the role of quick reactions in sports for several years, I jumped to the potential conclusion (i.e. hypothesis) that dark eyes are associated with the ability to make quick reactions. That started me thinking some more.

It occurred to me that eye darkness (not race or skin color) was the key dimension that could incorporate all the data. I thought in terms of eye darkness rather than eye color because, fortunately, I had been looking at black and white photographs in the magazine.

Also, it occurred to me that eye darkness, as a variable to study scientifically, had the advantage, unlike race, of retaining similar meaning across species. The more I thought about it, the more I thought of eye color, or eye darkness, as potentially important in scientific research.

[…]

A series of studies were done at Penn State University by Daniel Landers and his colleagues to test what has been called the “Worthy reactivity hypothesis.” This is my idea that dark eyes are associated with quick reactions. (The hypothesis is not suggesting anything about you or anyone else as an individual.) After finding the hypothesis confirmed in seven straight studies using laboratory equipment designed to detect small differences in reaction time, they calculated that the chance that dark eyes are not associated with quick reactions is less than one in ten million. I can live with those odds of being wrong.

They demonstrated that the results were not related to differences in skin color. It is an eye-darkness phenomenon. Most of their studies involved comparing brown-eyed Caucasians with blue-eyed Caucasians.

[…]

Partly because the differences between humans were small in absolute terms, I started in the 1970s to collect, mostly from field guides, published information on eye color for different species of land vertebrates. By the time this database, in its final form, was published in 2000, my wife and I had found published information on eye colors for 5,620 species of land vertebrates. Thousands were species of birds, hundreds were species of amphibians, reptiles or mammals. I need to make clear that my reactivity hypothesis is intended, now, to apply only to adult land vertebrates–not children, fish or invertebrates.

After comparing eye color information to behavioral information, it seems to me that the pattern holds across all classes of land vertebrates. One can see this by looking, first, at birds and bats. It is only the darkest-eyed families (mostly comprised of species with black or dark brown iris colors) that specialize in feeding on the wing in an open environment. That behavior is very dependent on speed and quick reactions. At the human level, that is analogous to outfielders in baseball; they, too, must have the speed, quick reactions, and developed skills to catch flies in an open environment.

At the other extreme, lightest-eyed, one finds herons. Their eye colors are mostly not dark at all, but yellowish, as are the eyes of families of frogs, cats, geckos and vipers. (These are the lightest-eyed large families in our database and come from all four classes of land vertebrates.) These animals are all hunters that lie-in-wait or slowly stalk prey before a sudden strike or pounce. All have some form of spring-loaded anatomy, such as folded neck, coiled tongue, or coiled body, that aids in making a sudden strike. At the human level, this is somewhat analogous to a slow-running quarterback in American football who, nevertheless, manages to be successful because of his ability and developed skill to just wait, with cocked arm, in a “pocket” of blockers, until the right moment to make a sudden strike downfield to an open receiver. Waiting, good timing and sudden release are all critical elements in the sequence.

It is easy enough to see in nature that yellow-eyed predators and black-eyed predators differ. Yellow-eyed predators use a tactic of WAIT WITHOUT MOVING. Black-eyed predators, such as those that feed on the wing, rely on a tactic of MOVE WITHOUT WAITING. Animals with eye darkness in the midrange between yellowish colors and dark brown or black (blue, green, gray, orange, red, hazel, light brown, brown) tend not to be skilled hunters, but, rather, rely more on finding immobile food (e.g. fruit, carrion, grubs, grass, eggs, ants, spiders). I have characterized this behavior as self-paced, or CAN WAIT. At least on the timing dimension, this is analogous in human sports to activities that are self-paced, such as pitching in baseball, shooting free throws in basketball, and the sports of golf and bowling.

[Land vertebrates that can hunt in total darkness tend to be dark-eyed and rely heavily on KEEN senses other than vision-such as hearing (e.g. Barn owls), touch (e.g. Boat-billed heron) or smell (e.g. pittas).]

To make sure that I was not “cherry-picking” my observations, I had twenty-one ornithologists make blind ratings of quick-versus-deliberate behavior for large families of birds. Those ratings confirmed that, in birds, controlling for differences in size, light eyes were associated with deliberate behavior and dark eyes were associated with quick behavior. Herons were rated as most deliberate and swifts received the highest ratings for quickness.

In a controlled lab experiment, researchers implanted gut microbes from two large-brain primate species (human and squirrel monkey) and one small-brain primate species (macaque) into microbe-free mice:

Within eight weeks of making changes to the hosts’ microbiomes, they observed that the brains of mice with microbes from small-brain primates were indeed working differently than the brains of mice with microbes from large-brain primates.

In the mice with large-brain primate microbes, the researchers found increased expression of genes associated with energy production and synaptic plasticity, the physical process of learning in the brain. In the mice with smaller-brain primate microbes, there was less expression of these processes.

“What was super interesting is we were able to compare data we had from the brains of the host mice with data from actual macaque and human brains, and to our surprise, many of the patterns we saw in brain gene expression of the mice were the same patterns seen in the actual primates themselves,” Amato said. “In other words, we were able to make the brains of mice look like the brains of the actual primates the microbes came from.”

Another surprising discovery the researchers made was a pattern of gene expression associated with ADHD, schizophrenia, bipolar and autism in the genes of the mice with the microbes from smaller-brain primates.

In 2013, scientists discovered that reindeer eyes change hues with the seasons:

If you look into the eyes of an Arctic reindeer (Rangifer tarandus) in the summer, when the days are long and the Sun is bright, you will see shining back a gold and turquoise glow, similar to the emerald reflection of cats’ eyes in the night.

In wintertime, however, when darkness reigns, a reindeer’s eye does something unique. It turns a stunning, deep blue.

[…]

Reindeer feed at twilight, and during the Arctic winter, twilight can last for more than a third of the day, casting an extremely blue light over the icy landscape.

[…]

To aid in the reindeer’s ability to see lurking wolves and yummy lichen in the dimness, scientists think that the animal’s eyes may have evolved to reflect more blue light in winter. This gives the low light another pass through the retina, allowing more information to be gleaned by the eye’s photoreceptors.

As such, the reindeer gets a brighter view of the twilit landscape (up to a thousand times brighter), but the trade-off is an image with significantly less resolution, like looking through misted glass.

[…]

In 2022, Fosbury and colleagues studied the difference between the eyes of reindeer that had died in summer and those that had died in winter.

Their findings support the idea that constant dilation of the pupils in low light affects the eyes’ fluid balance, possibly causing structural changes in the tapetum.

Primates originated in cold environments, not the tropics:

It is easy to see why scientists had assumed primates evolved in warm and wet climates. Most primates today live in the tropics, and most primate fossils have been unearthed there too.

But when the scientists behind the new study used fossil spore and pollen data from early primate fossil environs to predict the climate, they discovered that the locations were not tropical at the time. Primates actually originated in North America (again, going against what scientists had once believed, partly as there are no primates in North America today).

Some primates even colonized Arctic regions. These early primates may have survived seasonally cold temperatures and a consequent lack of food by living much like species of mouse lemur and dwarf lemur do today: by slowing down their metabolism and even hibernating.

Challenging and changeable conditions are likely to have favored primates that moved around a lot in search of food and better habitat. The primate species that are with us today are descended from these highly mobile ancestors. Those less able to move didn’t leave any descendants alive today.

A couple small mutations helped turn skittish animals into the creatures humans could saddle and ride:

Researchers led by Xuexue Liu and Ludovic Orlando analyzed horse genomes spanning thousands of years, tracking 266 genetic markers tied to traits like behavior, body size, and coat color. Their results, published in Science, suggest that early domestication didn’t begin with flashy coats or taller frames. Instead, the first breeders unsurprisingly selected for temperament.

One of the earliest signals of selection appeared at the ZFPM1 gene, linked in mice to anxiety and stress tolerance. That genetic shift, around 5,000 years ago, may have made horses just a little calmer — tame enough for people to keep close.

But the real game-changer came a few centuries later. Around 4,200 years ago, horses carrying a particular version of the GSDMC gene began to dominate. In humans, variants near this gene are associated with chronic back pain and spinal structure. But for horses and lab mice, the mutation reshapes vertebrae, improves motor coordination, and boosts limb strength. In short, it made horses rideable.

The numbers are staggering. The frequency of the GSDMC variant shot from 1% to nearly 100% in just a few centuries. Laurent Frantz of Ludwig-Maximilians-Universität München, who wrote an accompanying commentary, calls the selection “almost unprecedented in evolution.” For comparison, the human mutation that lets adults digest milk — a trait with huge survival advantages — spread far more slowly, with a selection strength of only 2–6%.

“The right conditions for the rise of the rideable horse materialized ~3,500 years ago in the Eurasian Steppe, north of the Caspian Sea,” Frantz explained. That’s when local cultures began seeking animals for war and transport rather than food. The genetic stars aligned: rare mutations already present in wild horses met human ambition.

Time magazine announces the return of the dire wolf:

The dire wolf once roamed an American range that extended as far south as Venezuela and as far north as Canada, but not a single one has been seen in over 10,000 years, when the species went extinct. Plenty of dire wolf remains have been discovered across the Americas, however, and that presented an opportunity for a company named Colossal Biosciences.

Relying on deft genetic engineering and ancient, preserved DNA, Colossal scientists deciphered the dire wolf genome, rewrote the genetic code of the common gray wolf to match it, and, using domestic dogs as surrogate mothers, brought Romulus, Remus, and their sister, 2-month-old Khaleesi, into the world during three separate births last fall and this winter—effectively for the first time de-extincting a line of beasts whose live gene pool long ago vanished. TIME met the males (Khaleesi was not present due to her young age) at a fenced field in a U.S. wildlife facility on March 24, on the condition that their location remain a secret to protect the animals from prying eyes.

The dire wolf isn’t the only animal that Colossal, which was founded in 2021 and currently employs 130 scientists, wants to bring back. Also on their de-extinction wish list is the woolly mammoth, the dodo, and the thylacine, or Tasmanian tiger. Already, in March, the company surprised the science community with the news that it had copied mammoth DNA to create a woolly mouse, a chimeric critter with the long, golden coat and the accelerated fat metabolism of the mammoth.

If all this seems to smack of a P.T. Barnum, the company has a reply. Colossal claims that the same techniques it uses to summon back species from the dead could prevent existing but endangered animals from slipping into extinction themselves.

[…]

It takes surprisingly few genetic changes to spell the difference between a living species and an extinct one. Like other canids, a wolf has about 19,000 genes. (Humans and mice have about 30,000.) Creating the dire wolves called for making just 20 edits in 14 genes in the common gray wolf, but those tweaks gave rise to a host of differences, including Romulus’ and Remus’ white coat, larger size, more powerful shoulders, wider head, larger teeth and jaws, more-muscular legs, and characteristic vocalizations, especially howling and whining.
The dire wolf genome analyzed to determine what those changes were was extracted from two ancient samples—one a 13,000-year-old tooth found in Sheridan Pit, Ohio, the other a 72,000-year-old ear bone unearthed in American Falls, Idaho.

[…]

Colossal’s dire wolf work took a less invasive approach, isolating cells not from a tissue sample of a donor gray wolf, but from its blood. The cells they selected are known as endothelial progenitor cells (EPCs), which form the lining of blood vessels. The scientists then rewrote the 14 key genes in the cell’s nucleus to match those of the dire wolf; no ancient dire wolf DNA was actually spliced into the gray wolf’s genome. The edited nucleus was then transferred into a denucleated ovum. The scientists produced 45 engineered ova, which were allowed to develop into embryos in the lab. Those embryos were inserted into the wombs of two surrogate hound mixes, chosen mostly for their overall health and, not insignificantly, their size, since they’d be giving birth to large pups. In each mother, one embryo took hold and proceeded to a full-term pregnancy. (No dogs experienced a miscarriage or stillbirth.) On Oct. 1, 2024, the surrogates birthed Romulus and Remus. A few months later, Colossal repeated the procedure with another clutch of embryos and another surrogate mother. On Jan. 30, 2025, that dog gave birth to Khaleesi.

[…]

“The idea that we could just take a vial of blood, isolate EPCs, culture them, and clone from them, and they have a pretty high cloning efficiency, we think it’s a game changer,” says George Church, Colossal co-founder, and professor of genetics at both Harvard University and the Massachusetts Institute of Technology. The less invasive cell-sampling process will make the procedure easier on animals, and the fact that Colossal’s methods worked on this early go-round boosts company confidence that they are on track for much broader de-extinction and rewilding.

Borrowing a name from Game of Thrones for a dire wolf makes perfect sense, but Khaleesi? The actual (fictional) dire wolves in the stories are:

Grey Wind, adopted by Robb Stark.
Lady, adopted by Sansa Stark.
Nymeria, adopted by Arya Stark.
Shaggydog, adopted by Rickon Stark.
Summer, adopted by Bran Stark.
Ghost, adopted by Jon Snow.

Scientific purists will note that the “dire wolves” created by Colossal are merely ordinary wolves with a few gene edits. Previous “dire wolves” have been dogs bred to look like wolves.

In addition to seeds and nuts, California ground squirrels also eat voles:

“This was shocking,” said Jenn Smith, an ecologist at the University of Wisconsin-Eau Claire. “We had never seen this behavior before.”

For the study, scientists observed squirrels in a regional park near the San Francisco Bay and consistently saw the creatures hunting down voles. Such sightings, recorded in videos and photographs, coincided with a surge in vole numbers at the height of summer. The research, published in the Journal of Ethology, is the first to find a significant number of squirrels eating meat.

“I could barely believe my eyes,” said coauthor Sonja Wild, a postdoctoral researcher at UC Davis. “From then, we saw that behavior almost every day. Once we started looking, we saw it everywhere.”

Researchers recently identified dietary prey species from hair compacted in the teeth of two Tsavo lions that lived during the 1890s in Kenya — the dreaded Man-Eaters of Tsavo:

Analysis of hair DNA identified giraffe, human, oryx, waterbuck, wildebeest, and zebra as prey and also identified hair that originated from lion.

A dye that helps to give Doritos their orange hue can also turn mouse tissues transparent, researchers have found:

Applying the dye to the skin of live mice allowed scientists to peer through tissues at the structures below, including blood vessels and internal organs.

[…]

The technique works by changing how body tissues that are normally opaque interact with light. The fluids, fats and proteins that make up tissues such as skin and muscle have different refractive indices (a measurement of how much a material bends light): aqueous components have low refractive indices, whereas lipids and proteins have high ones. Tissues appear opaque because the contrast between these refractive indices causes light to be scattered. The researchers speculated that adding a dye that strongly absorbs light to such tissues could narrow the gap between the components’ refractive indices enough to make them transparent.

[…]

Several candidates emerged, but the team focused on tartrazine, or FD&C Yellow 5, a common dye used in many processed foods. “When tartrazine is dissolved in water, it makes water bend light more like fats do,” says Hong. A tissue containing fluids and lipids becomes transparent when the dye is added, because the light refraction of fluids matches that of lipids.

[…]

The researchers demonstrated tartrazine’s ability to render tissues transparent on thin slivers of raw chicken breast. They then massaged the dye into various areas of a live mouse’s skin. Applying the dye to the scalp allowed the team to scrutinize tiny zigzags of blood vessels; putting it on the abdomen offered a clear view of the mouse’s intestines contracting with digestion, and revealed other movements tied to breathing. The team also used the solution on the mouse’s leg, and were able to discern muscle fibres beneath the skin.

The technique can make tissues transparent only to a depth of around 3 millimetres, so it is currently of limited practical use for thicker tissues and larger animals.

I was immediately reminded of H.G. Wells’ Invisible Man:

“But I went to work—like a slave. And I had hardly worked and thought about the matter six months before light came through one of the meshes suddenly—blindingly! I found a general principle of pigments and refraction—a formula, a geometrical expression involving four dimensions. Fools, common men, even common mathematicians, do not know anything of what some general expression may mean to the student of molecular physics. In the books—the books that tramp has hidden—there are marvels, miracles! But this was not a method, it was an idea, that might lead to a method by which it would be possible, without changing any other property of matter—except, in some instances colours—to lower the refractive index of a substance, solid or liquid, to that of air—so far as all practical purposes are concerned.”

“Phew!” said Kemp. “That’s odd! But still I don’t see quite … I can understand that thereby you could spoil a valuable stone, but personal invisibility is a far cry.”

“Precisely,” said Griffin. “But consider, visibility depends on the action of the visible bodies on light. Either a body absorbs light, or it reflects or refracts it, or does all these things. If it neither reflects nor refracts nor absorbs light, it cannot of itself be visible. You see an opaque red box, for instance, because the colour absorbs some of the light and reflects the rest, all the red part of the light, to you. If it did not absorb any particular part of the light, but reflected it all, then it would be a shining white box. Silver! A diamond box would neither absorb much of the light nor reflect much from the general surface, but just here and there where the surfaces were favourable the light would be reflected and refracted, so that you would get a brilliant appearance of flashing reflections and translucencies—a sort of skeleton of light. A glass box would not be so brilliant, nor so clearly visible, as a diamond box, because there would be less refraction and reflection. See that? From certain points of view you would see quite clearly through it. Some kinds of glass would be more visible than others, a box of flint glass would be brighter than a box of ordinary window glass. A box of very thin common glass would be hard to see in a bad light, because it would absorb hardly any light and refract and reflect very little. And if you put a sheet of common white glass in water, still more if you put it in some denser liquid than water, it would vanish almost altogether, because light passing from water to glass is only slightly refracted or reflected or indeed affected in any way. It is almost as invisible as a jet of coal gas or hydrogen is in air. And for precisely the same reason!”

“Yes,” said Kemp, “that is pretty plain sailing.”

“And here is another fact you will know to be true. If a sheet of glass is smashed, Kemp, and beaten into a powder, it becomes much more visible while it is in the air; it becomes at last an opaque white powder. This is because the powdering multiplies the surfaces of the glass at which refraction and reflection occur. In the sheet of glass there are only two surfaces; in the powder the light is reflected or refracted by each grain it passes through, and very little gets right through the powder. But if the white powdered glass is put into water, it forthwith vanishes. The powdered glass and water have much the same refractive index; that is, the light undergoes very little refraction or reflection in passing from one to the other.

“You make the glass invisible by putting it into a liquid of nearly the same refractive index; a transparent thing becomes invisible if it is put in any medium of almost the same refractive index. And if you will consider only a second, you will see also that the powder of glass might be made to vanish in air, if its refractive index could be made the same as that of air; for then there would be no refraction or reflection as the light passed from glass to air.”

“Yes, yes,” said Kemp. “But a man’s not powdered glass!”

“No,” said Griffin. “He’s more transparent!”

Researchers have reported the first known infection of an exotic eye worm in a black bear in the US, which was killed in Pennsylvania in November 2023:

The bear had at least 13 adult parasitic worms pulled from its eyes, and the researchers identified them as the invasive, potentially blinding species Thelazia callipaeda, which was only first detected in the US in 2020.

T. callipaeda is a nematode previously known for spreading in Asia and Eastern Europe, where it plagues carnivores, rabbits and hares, rodents, and primates (including humans). But it has recently undergone a swift and massive expansion in its range, including to Western Europe and North America. The initial 2020 detection in the US was in an eye of a pet dog in New York that had no travel history. Since then, it has shown up in at least 11 dogs — in New York, New Jersey, Connecticut, and Nevada — and two cats in New York, according to a study published in February. (The travel history of the Nevada dog is unknown, so it’s unclear where that infection occurred.)

In the new study, the UPenn researchers noted that the adult female bear with the T. callipaeda infection was “legally harvested” in Monroe County. The infection was detected as it was being processed for taxidermy. The researchers noted that two other bears harvested in the area had similar eye worm infections, but those cases were not investigated to determine the type of worms.

[…]

The worm spreads via a variegated fruit fly, Phortica variegate, that feasts on the tears and salty eye secretions of various mammals. There’s only limited data on P. variegate‘s distribution in the US. But it’s clearly an effective vector for the worm and efficient at delivering the parasite to new hosts.

The fruit fly’s role is not just to transport T. callipaeda, but also to help it grow. The life cycle of the worm starts in a host’s eye, where early-stage (L1) larvae are released by adult female worms and picked up by a male fly. The fly then becomes infected, with the larvae going through two developmental stages in the fly’s testes. When they’re ready, the third-stage (L3) larvae migrate to the fly’s mouthparts, where they can be transferred to a new host.