The Shapes that Animals’ Pupils Have

Not Just Little Black Holes

English is a language of ‘homonyms’ as our English, French and Russian teacher Bruno Mannewitz used to say. Many English words sound the same but mean totally different things. Mean and mean, current and current, bat and bat, bark and bark and, of course pupil and pupil come to mind. (On the other hand words that sound the same but are spelt differently like soar and sore, you and ewe, cell and sell, etc. are homophones and equally numerous). This essay, however, is about ‘pupils’, i.e., gaps in the eyes’ iris through which light passes on its way to the retina. That the size of our pupil changes and turns into a tiny circular “black hole” when the ciliary muscle (an involuntary,  smooth and not striated muscle) contracts, yes ‘contracts’ is known! But in human eyes only the pupil’s diameter changes upon an exposure to light;  in some animals, the shape of the pupil changes as well.

Among animals one can find pupils of a variety of sizes and shapes, and it has repeatedly been tried to correlate the way a pupil looks with the way an animal lives and behaves. A pupil like that of the domestic cat, which appears as a vertical slit under illumination, has been linked with small ambush predators that require good distance estimations. It can also be encountered in many birds, reptiles and sharks; not all of them, however, being small if we think of crocodiles and, for example, the lemon shark. Large predators such as tigers and lions, which like the domestic cat may hunt during the day as well as during the night, possess circular pupils like humans. Such pupils will dilate, i.e. increase in diameter at night and contract during the day, giving the predator a superior sensitivity to the dim light available at night and a better acuity, i.e. resolving power during daylight hours.

Pupils that look like horizontal slits are easily observable in sheep and goats, animals in other words that are grazers and in constant danger of being attacked by a predator. The horizontal pupil  provides an excellent field of view of the horizontal surroundings, the area in front and around the animal, but not above it (attacks are not likely to come from there). That, however, is different for creatures of the ocean that do face dangers from above and this could explain the weird often ‘W-shaped’  pupils seen in many squid or the horse-shoe or crescent-shaped pupils of sting-rays and related rhinobatid guitar fish. Given sunny flickers of light from above and dimmer more stable light conditions from below, such unusually shaped pupils are thought to even out the effects of light distortions, excluding unwanted light and shadows and providing the animal with a large visual field.

Perhaps some of the weirdest pupils can be found among some geckos that possess beaded pupils with vertically arranged wider and narrower regions in between. How to relate that to their lifestyle and behaviour is hard to understand and something else, too, is: which has been puzzling me since childhood when I kept Hyla arborea tree frogs and common toads. The latter had beautifully golden horizontal pupils, often considered to be typical of prey animals (but toads are not preyed upon by many species), while the former, when sitting on a horizontal surface, had vertical pupils, commonly seen as a sign of a small ambush predator. However, tree frogs do not always sit horizontally on a leaf but frequently cling vertically to a surface (like they did when resting on the glass walls of my terrarium). Will their vertical pupils then not be oriented horizontally?  And grazing animals like goats with normally horizontal pupils, aren’t the latter vertical when the animal grazes with its head down? Martin Banks et al. in a 2015 article in “Science Advances” have shown that when goats and other grazing animals put their heads down, their eyes rotate to maintain the pupils’ horizontal alignment!  But did the eyes of my tree frogs also rotate?  Alas, it’s too long ago; I can’t remember.

© Dr V.B. Meyer-Rochow and, 2022. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

Riding a Cicada

Sounds More than Odd, but Epipomponia nawai Babies Do

As a child during strolls along a railway track with my grandfather, we sometimes stopped to see if we could spot the caterpillars that had eaten holes into some of the leaves of the plants we encountered. One of the most exciting finds at that time, for me anyway, were the huge caterpillars of the Sphinx ligustri moth. I loved to collect various butterfly caterpillars and managed to rear some to adulthood. I was reminded of these childhood exploits when in late August on the balcony just outside my flat on the 15th floor in South Korea, I picked up a seemingly distressed cicada that was unable to fly away. Being curious why it had behaved in this funny way I took a closer look and  -lo and behold-  I found a white insect larva “riding on its back”, actually clinging to its abdomen! My childhood experience told me that this looked like a caterpillar and was not a maggot of a fly or the larva of a parasitic wasp. What was it?

To my great surprise, examining the still fully alive albeit weak cicada and its “rider” under a magnifying glass, I had to conclude that the “thing” was indeed a caterpillar. But with very, very few exceptions like the famous ant-larvae consuming lycaenid butterfly species and the weird insectivorous fly-catching predatory caterpillars of the Hawaiian geometrid moth genus Eupithecia (that I reported on in the essay on “Non-conformists”), caterpillars feed on plants and certainly not on those highly mobile and active cicadas. Or do they?

The mystery was solved when I located some publications that described a species of moth, known as Epipomponia nawai, whose larvae when leaving their eggs, somehow manage to ‘board’ a cicada and then hang on for dear life, sucking body fluids of their host and/or feeding on its cuticle. How exactly the baby caterpillar finds its host and how it then grows and matures  – all on the outside of its cicada host- until it is ready to pupate, are unsurprisingly aspects of this moth’s life cycle that are still not fully known. The specimen that I “looked after” pupated two days later, when the cicada lay in its death throes and could hardly move at all anymore. The then about 10 mm long, white caterpillar constructed a fluffy silky pupal case and I hoped to see the adult soon. Alas, the pupa did not develop, and I had to be satisfied with some information available from two or three publications on this species of parasitic moth.

There are apparently no more than 32 known species of parasitic moths worldwide, all belonging to the Epipyropidae. Although present on all continents except Antarctica, they are nowhere very common and opportunities to carry out behavioural and physiological studies are very limited. One of the best and most detailed observations on the species is that of the Japanese entomologist R. Ohgushi from 1953. He describes several cicada host species and shows that sometimes more than one caterpillar ride on a single host. He also examined the darkly coloured adults of the moth that emerged from the pupae 10-15 days later and credits them with wing spans of 15 to 20 mm. Those available to him died a few days after they had left the pupa and laid some sticky eggs on grass blades or tree bark. It has become known since Ohgushi’s study that the eggs of this moth can also develop without being fertilized. However, how the feeble and miniscule baby caterpillars find and climb on their cicada hosts remains a total mystery.

In Europe a related ‘parasitic moth species’ of the same family, known as Ommatissopyrops lusitanicus, has been described from Spain and Portugal. It parasitises the datepalm pest bug Ommatissus binotatus. My hunch is that there may well be some more hitherto undescribed species of parasitic moths that have gone unnoticed so far. Perhaps people spending their summer vacation in the Mediterranean can take a look at cicadas and plant hoppers and discover a new species. I think that that is entirely possible.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

Posting Live Animals in the Mail

How to send live animals through the mail? That was the question I faced when I needed to get firebelly newts (Cynops pyrrhogaster) from the Japanese island of Hachijojima (where I lived) to Okinawa, where a geneticist lived, who was to determine from where the Hachijojima newt population originally came. Newts, being amphibians, are prone to desiccation and need to be packed carefully with moist moss in a flat plastic container with a few tiny aeration holes. I prepared two packages with 6 newts each, went to the post office and declared the two items to be mailed as “Scientific Specimens”. I never had to say that the 2 packages contained live newts. When because of bad weather airplanes did not fly to Hachijojima for three days and the newts did not arrive in Okinawa until 8 days later, I was worried my animals might have died. But luckily they arrived in a healthy condition, were genetically studied and compared with other populations in Japan and revealed that they all must have come from Shikoku and not, as had been assumed, from the much closer region of Chiba Prefecture. But was it legal to send them by mail?

Which animals you can and can not send in the mail depends on international postal agreements and on local regulations. In countries of the European Union vertebrate animals will usually not be accepted by the post and will have to be transported by private carriers. However, even such non-governmental private carrier companies have to obey existing animal protection and welfare regulations that stipulate cage material and dimensions, adequate ventilation, supplies of food and water during transport if deemed necessary and, of course, safety concerns. Regarding invertebrates, live honey bee queens (and workers in small quantities) and live Drosophilidae fruit flies (for biological research) are permitted, just like silkworm caterpillars, leeches and a few other beneficial invertebrates. For the bees the most popular cage has 2 compartments; a larger to house the queen and 6-12 attendant worker bees and a smaller with a mixture of powder sugar and about 20% honey. Water is not necessary, but there should be ventilation holes in the envelope and a label of “Live bees” and “Protect against sunshine” on it.

In the United Kingdom not only live honey bees, caterpillars, stick insects, cockroaches and crickets, maggots, earthworms, leeches and spiders, but also some live fish can be sent by mail  – provided the latter are classified as fish fry or eggs. It always surprises people to hear that certain fish can be sent in the mail, but to be honest it needs to be pointed out that what can be sent in an envelope are not the adult fish but their desiccation-hardy eggs, the so-called ‘annual eggs’. The family of fish I am referring to are the killifish (Cyprinodontidae) with more than a thousand small and colourful, mostly freshwater species of fish. The fish inhabit small streams in the Americas, Africa and Asia which frequently dry up. That kills the adults but not their eggs, which survive in the mud for several weeks and even months until it rains and their habitat is filled with water. The eggs then resume their development and the baby fish hatch. Eggs of rare and protected species are, of course, not permitted to be collected or sent.

The USA postal authorities not only allow bees and other invertebrates to be sent by mail, but also small, harmless, cold-blooded animals like toads, frogs, newts and lizards with the exception of snakes, turtles and turtle eggs. Live birds, if not too large or protected by law, can also be sent, which includes live, one day-old poultry. That the packaging meets the requirements of the Animal Welfare Act is understood as the animals must not suffer during air or surface transport. Not allowed in probably any country of the world is to send mammals in the mail. However, that didn’t deter Reg Spiers in 1964 to post himself in a wooden box from England to Australia: he didn’t have the money for a ticket. He chose cash-on-delivery and after arriving at Perth Airport and being placed in a storage shed, he climbed out of his box, left the storage area unnoticed and got home. (His story)

© Dr V.B. Meyer-Rochow and, 2022. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.