A new tenant for the snail’s shell

Empty land snail shells are prime real estate for many invertebrates that are small enough to fit in them. Several species of bees, wasps, spiders, ants and pseudoscorpions are known to build nests or hide in snail shells. Last December I was lucky to witness a previously unrecorded insect-snail shell association. In this case the insect was an unidentified species of thrips (Thysanoptera) and the empty shells was the common North American snail Zonitoides arboreus.

A tentative familial assignment for the said thrips was given as Phlaeothripidae (tube-tailed thrips) after I posted these pictures on BugGuide.net.

You can read the details in this paper that just came out in the current issue of Triton.

The resemblance is harmonious

This one-armed statue of Johann Sebastian Bach that I photographed at the Middelheim Outdoor Sculpture Museum in Antwerp, Belgium last July (and which already illustrated this post) shows the composer as we have always known him. But now, according to this Reuters news article, Scottish anthropologist Caroline Wilkinson thinks the good ol' Seb might have actually looked like this.


Despite the claims to the contrary in the Reuters article, I do see some resemblance between the statue and the digital creation. What I don't understand is how she figured out from Bach's bones what his hair looked like.

An intruder in Chincoteague

An unexpected find during my Chincoteague expedition last October* was a couple of shells of the European land snail Helix aspersa (= Cornu aspersum). Both shells, one adult and the other juvenile, were attached to the back wall of a small commercial building. Below is an in situ picture of the juvenile shell.

The adult shell was empty, but the juvenile shell still had the remains of its former occupant. You can read the details in this paper that just came out in the current issue of Triton.

I have no idea how the snails had been introduced to that location where there has also been, for the past several years, a vigorous colony of another alien snail Cernuella cisalpina. I will probably go back to Chincoteague in the future and check out the snails in that particular location and elsewhere.


Stories from Chincoteague are here, here, here, here, here, .

Species vulnerability traits

Near the end of October 2007, there was a workshop in London hosted by IUCN Species Survival Commission and some other organizations. The report of the workshop is available here.

The workshop attendants put together a list of species traits that they considered to be "indicative of vulnerability to extinction due to a range of threats and generally applicable across all taxonomic groups." I think this list will be quite useful in assessing extinction risks of threatened species.

I have a few comments.

•The potential protection offered to a species against climate changes by its microhabitat is one of the traits under the category Range characteristics. Can any animal species be perennially buffered against the drastic climate changes that may be taking place in its overall environment? This is an intriguing question. Microhabitats, by maintaining a more or less stable microclimate, could indeed provide protection against macroclimatic changes for short periods. But I think they would fail sooner or later. For example, many invertebrates take refuge under rocks where they find a humid habitat away from sunlight and predators; the undersides of rocks are their microhabitat. But, for example, if there were a long-term drought or a permanent change in rainfall patterns (macroclimate), the microclimate of the microhabitats would also gradually change. Nevertheless, at least for the assessment of the short-term risks a particular species is facing, the characteristics of its microhabitat certainly need to be taken into account.

•A trait listed under the category of Breeding system is self incompatibility. I don't know what that means. But what is missing is the ability to self, which refers to the ability of a hermaphroditic animal, for example, a terrestrial pulmonate snail, to fertilize its eggs with its own sperm. This would be a critically vital trait during times when the population of a species may be thinned out and mates may be hard to come by.

•A requirement to experience a cold-induced dormancy prior to reproduction (vernalization) that I discussed here and here would be covered under the category Phenology. Although vernalization per se is not mentioned in the list of phenological cues, various reproductive behaviors and climatic triggers are included.

Let them eat French fries

The arrogant French got a dose of their own medicine when Turkey blocked Gaz de France's bid to join the Nabucco natural gas pipeline project, a consortium of companies that will bring Central Asian oil to Europe. The Turks' move was in retaliation against the recent French legislation making it a criminal offense to deny that the deaths of thousands of Armenians in 1915 in the Ottoman Turkey constituted genocide. What better way is there to stifle freedom of speech than by making—solely for political gains—the expressions of arbitrarily selected ideas and opinions illegal?

The International Herald Tribune has published a sensible opinion piece on the issue.

Boxcar graffiti LV, LVI & LVII

Sandbox for shells

When I am measuring a large lot of snail shells I often need to know which measurement is associated with which shell so that if I need to re-examine the shells in the future for whatever reason, I will not have to measure them again. Frequently, there are also specimens with unusual features that need to be set aside for further examination. The easiest thing to do is to write numbers on the shells. But that is feasible only if the shells are large. One may also keep each shell in a numbered gelatin capsule if there are enough capsules available.

Another solution is to place the shells in coded positions inside a suitable container. Corrugated cardboard works well for that purpose. I usually number each column and assign a letter to each row. Here are some Albinaria caerulea shells lined up in the grooves of a sheet of corrugated cardboard. Of course, the locality information must always be kept with the shells.

Sometimes I use a small box filled with sand to position large shells for photography. Recently I learned that paleontologists use large sandboxes when they are assembling fossil bones from fragments (examples from the VA Museum of Natural History Vertebrate Paleontology Lab are here and here). So a few day ago when I was measuring some shells of Orculella ignorata, a small land snail from Turkey and the adjacent Greek Islands, I thought of using a small sandbox to line up the shells.


The mean shell height of this lot of Orculella ignorata was 6.6 mm.
It worked well. The next time I am at a beach I have to remember to get more sand. I also have to stock up on Sour Alerts Extreme Orange Sour Candies.

Intelligent design repackaged

James Randerson of the Guardian has a 4-minute interview with Ken Miller available on podcast. They discuss design in evolution and the current state of intelligent design creationism.

So, it's a classic case of relabeling. Just as scientific creationism was relabeled intelligent design, intelligent design today in the U.S. has been relabeled as a critical analysis of evolutionary theory.

Ken Miller

Snow crystal photography

The return of cold weather with a minor snow storm provided opportunities for photographing snow crystals. Unlike the previous attempts (here and here), that were during the day using sunlight, the latest trials were at night using a flash.

Creating a suitable background that would bring out the details of the crystals was, once again, a major problem. In the 1st 4 pictures below, the crystals were on a glass plate that was raised above a piece of black cloth, while in the last picture the crystal was on a wooden surface.

Here are 3 crystals in a row.


And here is the leftmost crystal enlarged.


The next photo is the result of the serendipitous reflection of the flash from a crystal.


The last picture shows a peculiar crystal. Although it still retained its symmetry, it looks like it was starting to melt or had partially melted and then refrozen.


All of the pictures were taken outdoors using an Olympus E-500 with a 35 mm Zuiko lens attached to the camera via an Olympus 25-mm extension tube. Light was from an Olympus FL-36 flash attached to the camera with a flexible cable (Olympus FL-CB05). Both the camera and the flash were hand-held. Exposure details: 1/160 s at either f13 or f14 with an ISO setting of either 200 or 250. Exposure was controlled primarily by moving the flash closer or further away.

Slug Zen

The moon and the paper
Are the same white
The pupil of the eye and the ink,
Both black.
This mysterious meaning
Remains a circle,
Beyond the possibility
Of understanding.

Obaku Sokuhi (1611-1671)

From Daily Zen

Let me show you something else, Obaku. Two slugs in a circle. Both Limax maximus. Now, if that is not a mystery, what is?


...the origin of species—that mystery of mysteries...
The Origin of Species By Charles Darwin

Vagaries of translations

How much does a piece of complex text, especially a literary one, that was translated from one language to another retain the unique flavor, so to speak, of the original passage? A skilled translator can perhaps come close to duplicating the original in another language, but, alas, some words and phrases just cannot be translated. And sentences must often be rearranged during translation to make them sound better in the new language.

Here is a test I carried out last nite.

One of the best travel and adventure books I have read was On Horseback Through Asia Minor, Frederick Burnaby's account of his trip from Istanbul to Iran in the dead of the winter of 1876. I read the original English version several years ago. Curiously, the 1st Turkish translation didn't come out until the late 1990s, which I also have.

I picked a paragraph more or less at random from the Turkish version and translated it back into English without consulting Burnaby's original.

Here is the opening paragraph of Chapter 47 in the 1996 Oxford University Press edition, which corresponds to Chapter 15 in volume 2 of the 1877 edition available at Google Books. Burnaby was spending the nite in the house of an Armenian family in a small village in Eastern Turkey.

On Horseback Through Asia Minor By Fred Burnaby
Below is the Turkish version (translated by Fatma Taşkent) from the 1999 edition.


And finally, here is my back translation into English.

In the next room separated from us by only an approximately one yard high railing, alongside the Armenian’s relatives, a courier and a Kurd, there were buffaloes, cows, calves and pigeons. The Kurd had on his head a magnificent turban shaped like a bonnet. It was made of blue satin and embroidered with gold thread. It was clear that the man was very proud of his clothing. He told the Armenian that he had bought the turban in Erzurum and that after he finished enjoying it he was going to give it to his preferred wife.

The overall meaning of the back translation comes close to that of Burnaby's original, although the sentence structures are inevitably different. However, there are notable differences in some words and phrases.

•The Turkish version gives the height of the railing as one meter, I turned it into one yard, but it turned out that Burnaby had used three feet.
•For Burnaby's postman, the Turkish version uses ulak, of which I didn't know the meaning. According to my Turkish dictionary it means "messenger", which I translated into English as courier.
•Burnaby describes the Kurd's turban as being "adorned with gold thread"; the translator, however, took liberties and changed "adorned" into "embroidered".
•Likewise, in the next sentence Burnaby's "this attire" refers to the Kurd's turban, but the Turkish giysisinden literally means "of his clothing"; I would have used sarığından (of his turban) to match Burnaby's specificity.
•In the last sentence, Burnaby said that the Kurd was going to give the turban to his wife after he was finished wearing it. Once again, the translator put more meaning into Burnaby's words than he had intended: "hevesini almak" means to fully enjoy something that is new.

Note that Burnaby's last sentence was replaced by 2 separate sentences in the Turkish version. There is also an example here of the impossibility of translating certain phrases without changing the sentence structure. Burnaby's 2nd sentence starts with "The latter individual" in reference to the Kurd, but an equivalent phrase does not exist in Turkish. So the Turkish translator had to specify that it was the Kurd who was wearing a turban. In a different context, this could have affected the character of the narrative.

Innards of a tree

I chanced upon this tree during an after-lunch walk a week ago. The inward spiriling of its trunk attracted my attention.

Retractability into shell in snails

In shelled marine gastropods the ability to withdraw deeply into the shell is an escape mechanism from the predators, such as crabs, that break the shell starting at the aperture: the deeper a snail can withdraw into its shell the more likely it is to survive an attack. Despite the obvious evolutionary importance of retractability, not much has been written about it. The only malacologist who seems to have given serious thought to the subject is Geerat Vermeij. In his Evolution & Escalation (1987), he gives 2 advantages to a snail of being able to withdraw deeply into its shell. 1. Avoidance of detection by predators; if a snail can hide within its shell, a predator would be less likely to see it or detect it by chemical means; 2. Avoidance of capture or injury even if a predator breaks away the aperture and portions of the body whorl.

Vermeij also gives an example:

In laboratory trials at Guam, for example, I have found that the crab Calappa hepatica frequently removes a half whorl or more of the shell of Terebra affinis and then stops, even though the foot [of the snail] has not been reached. Probably the shell opening becomes so small that the crab's claws cannot gain a purchase on the shell to continue peeling.

I demonstrated the survival advantage of deep withdrawal in the case of the intertidal snail Batillaria minima in this paper and briefly discussed it in this post.

A snail can withdraw deep into its shell only if its shell is larger than the minimum size necessary to fully accommodate the snail’s body. This creates an evolutionary trade-off, because building a larger shell also has disadvantages. Vermeij mentions 2 in his A Natural History of Shells (1993): 1. Extra energy and resources required to build a larger shell; 2. Extra energy required to carry a larger shell.

I will add a 3rd disadvantage. Building a larger shell may also take time away from other activities, most importantly from reproduction, especially in species with determinate growth, which normally do not start reproducing until after they have completed shell growth.

I am trying to organize my ideas here in conjunction with a manuscript I am working on. Expect more posts along these lines in the near future.

Snail's Sprookje? Ja!

This morning I noticed in StatCounter that someone had translated this post from 2005 about vestigial shells of slugs into Dutch (I think) using Google. Here is the link to the translated page.

But why is it Snail's Sprookje? Isn't there a word for snail in Dutch?

Is it a boy or a girl?

I know you've always wanted to know how to sex an isopod but were afraid to ask. So, here is how you do it and you don't even have to kill the poor creature. First, you catch the isopod between your thumb and 1st finger*. (No, they don't bite and if you hold the isopod gently it will survive the process without any trauma.)

Then, you turn the isopod upside down and look between its hind legs (where else?). If it is a male, there will be at least a pair of long blade-like appendages lying flat near the isopod's posterior end (arrows in the picture below). Those are the modified endopodites of pleopods (inner branches of biramous abdominal limbs) that have evolved to perform the function of sperm transfer. I have magnified pictures of them in this post.


A male Armadillidium nasatum. The arrows point at the pair of modified pleopods.
The females, on the other hand, do not have any external genitalia. So, the absence of modified pleopods means the specimen is a female. It is best to try to sex the largest specimens; I don't know how early during their development the pleopods of males become easily distinguishable from those of females.


Full frontal nudity: this is a female Armadillidium nasatum. Compare with the picture of the male above. Isopods can also be captured and hold with light-weight tweezers.
If you don't have a stereomicroscope, a magnifying glass will help during these procedures.


*I learned this from Stephen Hopkin's A key to the woodlice of Britain and Ireland (Field Studies 7:599-650, 1991; also available as a separate booklet from the NHBS Environment Bookstore).

Sunday afternoon's beer review: Morocco Ale from England

A dark, smooth ale with a pleasant fruity aroma that I liked immediately. What is imparting that familiar yet "mysterious" aroma? It may be hops, but this is certainly not an India Pale Ale. I guess we will never know, unless we break into Levens Hall to steal the 300-year old secret recipe said to be kept there.

This beer has apparently nothing to do with its namesake country. According to the label and also the web page, the name Morocco may have been "associated with the dark Moors who came to the court when Catherine of Braganza married Charles II and brought Tangiers as part of her dowry." A dark beer named after "dark Moors", eh?

It comes in a larger than usual 500-ml bottle. At an alcohol content of 5.5%, one bottle gives you 27.5 ml of pure ethanol. Enough to add a few more healthy days to your life? Maybe.

Cheers!

Previous beer review was J.K. Scrumpy's Hard Cider.

His life as a tomb robber

In the spring of 1890, the 25-year old Sven Anders Hedin was appointed interpreter of a diplomatic team the King of Sweden was sending to the Shah of Persia. Before they left Stockholm, a Swedish professor of anthropology asked Hedin to bring back some skulls of Zoroastrians. (We can only guess at the racist motives of the professor, but those are besides the point in our story.)

In his memoirs, My Life as an Explorer (1925), Hedin tells the story of how he and a Swedish friend he had in Persia, Dr. Hybennet, fulfilled the skull collector's wishes.

Accordingly, in the middle of June, when summer was at its height, and the thermometer registered 106° in the shade, I set out with Dr. Hybennet for the Tower of Silence, the funeral-place of the fire-worshippers, southeast of Teheran. We chose the early hours of the afternoon for our raid, because then everybody kept indoors, on account of the heat.

We took with us a kurchin, or soft saddlebag, in the two pockets of which we put straw, paper, and two watermelons, each the size of a man's head.

At the Tower of Silence, where the Zoroastrians kept their dead in open graves for the vultures to clean the bones, they used a ladder to climb over the wall.

A rank, sickening smell of cadavers met us...There were sixty-one open, shallow graves. In about ten of them lay skeletons and corpses in various stages of putrefaction. Whitened and weather-beaten bones lay piled up alongside the wall.

After some deliberation, I selected the corpses of three adult men. The freshest corpse had been there only a few days; yet its soft parts, the muscles and entrails, had already been torn away and devoured by birds of prey. The eyes had been picked out, but the rest of the face remained, dried up, and as hard as parchment. I detached the dead man's skull and emptied it of its contents. I did the same with the second head. The third had been lying in the sun so long that its brains were dried up.
...
Then I emptied the bag, wrapped the skulls in paper, after first filling them with straw, and then put them in the bag in place of the watermelons. The bag thus retained its shape; and there was nothing to arouse the driver's suspicion, except the offensive smell, which may possibly have put strange ideas into his head.
...
The need for all this secrecy is obvious. What would the superstitious Persians and Parsees have thought of us, had they learned that we infidels were driving about, stealing skulls from their funeral-places?

He did get caught at the customs a year later when he was leaving Persia for Sweden with the skulls he and Hybennet had meticulously cleaned.

All my belongings were examined most carefully, and at last three round objects, wrapped in paper and felt, and resembling footballs, rolled out on the floor.
"What is this?" asked the customs inspector.
"Human heads," I answered, without blinking.
"I beg your pardon? Human heads?"
"Yes. Look, if you please!"
One of the balls was opened, and a skull grinned up at the inspectors.

Amazingly, they let him go with his skulls. Imagine that happening now.

Not that anything is wrong with tomb robbery.

Limax maximus mating - part 2

In the 1st part of this series, using some of the main literature references, I gave a brief description of how the slug Limax maximus mates.

One steamy August nite last summer, while checking out the evening creatures in my backyard, I saw 2 L. maximus going single file up a pine tree. I had never seen L. maximus mate before, but because I had read about it, I realized immediately that this was how it was supposed to start. Someone once said that chance favors the prepared mind; that was indeed true my case (having a camera at hand was also quite helpful).

Luckily the slugs didn't climb high, but stayed at a height that was very comfortable for picture taking.

After their climb ended, they started circling around each other.


Such circles always rotate in a clockwise direction, because the genital openings of dextral slugs are on the right sides of their heads. If they were rotating in a counterclockwise direction, their genital openings would not face each other.

This was followed by a sudden embrace and the twisting of their bodies around each other.


While they were rolling down the trunk, one slug had already everted its penis and the tip of the other slug's penis was visible.


Soon, their penises were fully everted and intertwined. Here is a close-up of their tips.


Finally, the penises expanded into a bell-shaped structure with a cool blue color. I suspect this is when they actually exchange spermatophores (cases of sperm).


The bell was present for only about 3 minutes and was followed by the withdrawal of the penises. You can see the tips of the disappearing penises of the still intertwined slugs in the next picture.


It was all over when one of the slugs quickly left the scene of their affair. But the other one remained behind and ate up the copious slime that they had secreted. The entire process, from the moment I took the 1st picture until the picture below, took 43 minutes.


The mating of L. maximus and several other species in the genus Limax, appears to be a very resource intensive way of exchanging sperm by a couple of hermaphrodites. Why not just do it on the ground like most other slugs? In fact, Limax flavus indeed mates on the ground.

Without elaborating, Leonard (2006) suggested that the mating behavior of L. maximus may have evolved under sexual selection. A talk by Gerhard Falkner & Barbara Klee at the World Congress of Malacology in Antwerp last July also discussed the possibility of sexual selection as the driving force behind the evolution of long penises in some members of the genus Limax. There is so much more to learn about these slugs. I can hardly wait until the next mating season!

Here is another set of pictures of mating L. maximus over at A Snail's Eye View.

The next part of this series will take a look at the genitalia of a dissected L. maximus.


Janet L. Leonard. 2006. Sexual selection: lessons from hermaphrodite mating systems.
Integrative and Comparative Biology 46:349-367. pdf

All the way from Mexico

We found 2 of these bugs* in a small container of organic raspberries bought in a store here in Maryland. According to the label on the container the raspberries had been grown in Mexico and were distributed by a company in California.

One of the bugs got washed down the drain and the other I saved. It was in a moribund state from the beginning, able to move its antennae and legs a little bit without actually being able to lift itself up. Nevertheless, it survived in that state for several days before expiring. I figured it was either from Mexico or California. I posted its pictures, along with a tentative genus to the best of my knowledge (which turned out to be wrong), here on BugGuide, but couldn't get an identification. Then I put the insect in a tube, included a label of information about where and when the raspberries had been purchased and gave the lot to a friend whose husband is an entomologist. That was back in early January.


The specimen made its way to the Maryland Department of Agriculture and in an e-mail that came this morning the bug was identified by them as Stenomacra cliens, family Largidae, a native of Mexico. There is a picture of a museum specimen here, where the genus is given as Theraneis.

Let's hope they are not establishing themselves in the U.S.


*Yes, they are true bugs, or hemipterans.

Limax maximus mating - part 1

In the ever-changing world of taxonomy, it is rare for an animal to be still called by the scientific name it received more than 200 years ago. The common slug Limax maximus is one such rarity: it was named by Linnaeus in 1758.

The well-known and often photographed mating of L. maximus takes place while a couple of slugs are suspending themselves using their mucus from an elevated point, commonly a tree branch or a wall. One of the most often cited descriptions of this process, and the one that gives the impression of being the oldest, is the one by Adams (1898). According to Hyman (1967), however, an earlier account was that of Ferussac & Deshayes (1819), which I have not had a chance to see yet. Recently, I discovered an even older description of the mating of L. maximus, but I will leave that story to a future post. A more recent account is that of Langlois (1965). There is also a series of photographs of mating L. maximus taken by someone named Lynwood M. Chace that were published in the magazine Discovery in 1952. The photographs were accompanied by a description of the mating, but it is not clear who actually wrote the text and it doesn't provide any new information that wasn't already known at that time.

Limax maximus seems to mate mostly in the evening. Briefly, the process is as follows: 2 slugs climb up a vertical surface, one leading the other; then they start circling each other; then they intertwine and suspend themselves by a thick strand of mucus; their penises evert and they too intertwine forming a bell-shaped structure at their lower end; the exchange of spermatophores presumably takes place within the bell; following this, the slugs abruptly separate and move away.

Below is one of Adam's drawing showing 2 mating slugs with their everted penises and the bell-shaped structure at their tips.

Here are 2 of Adam's more detailed drawings showing the morphology of the tips of the intertwined penises of the mating slugs.


Last August I was lucky to photograph the entire sequence of the mating of a couple of L. maximus in my backyard. Those photographs will be in part 2.


Adams, L.E. 1898. Journal of Conchology 9:92
Férussac, D. de & Deshayes, G.-P. 1819. Histoire naturelle générale et particulière des mollusques terrestres et fluviatiles, etc. Tome 1: 8 + 184 pp [not seen by me; cited in Hyman (1967).]
Hyman, L.H. (1967). The Invertebrates, vol. 6, Mollusca 1. McGraw-Hill. New York.
THOMAS H. LANGLOIS. 1965. The conjugal behavior of the introduced european giant garden slug, Limax maximus l., as observed on south bass island, lake erie. OHIO JOURNAL OF SCIENCE 65:298. pdf

A minor identity crisis from a long time ago

I am he as you are he as you are me and we are all together.
The Beatles, I Am the Walrus, 1967

A recurring theme in the nobelist Orhan Pamuk's novels involves identity switches between people. In The White Castle, a Venetian scientist trades places with an Ottoman scholar; in The Black Book, the protagonist assumes the identity of his journalist cousin and starts writing essays under his name.

More than 30 years ago, I personally experienced an identity switch of sorts, but unlike those in Pamuk's plots, mine is worth only a blog post.

It was the summer of 1977 and I was starting an internship in the chemistry laboratory of the textile factory in the city of Aydın in Turkey (yes, the city they named after me). On the first day they asked me for a photograph of myself for an ID card that was to be issued the following day. Back at home that evening, I mulled over my 2 choices: I could either waste time and money to get a picture of myself taken or use something already available around the house. But the only "suitable" picture I could find was a photograph of my cousin Metin that he had given me as a memento a few weeks earlier. It was an easy decision.

The next morning, I showed up at the factory, handed in "my" photograph while mumbling a preemptive excuse that it was not a recent picture lest someone noticed the lack of close resemblance between me and the person in the photograph. The man took it without so much as glancing at it. A few hours later, I had my ID card for the Kimya Lab. at Aydın Tekstil.


Ever since then, this card of mixed identities (still in existence, although now faded and discolored) has been a source of chuckles within the family.

But, seriously, who did that card really represent on those hot and muggy summer mornings when it was presented to the guard at the gate? Was it just me who showed up for work at the factory every morning for several weeks or was a part of Metin also tagging along me?

Holy cheese!

How would you describe the flavor of plain boiled chicken, or of something with more taste, say, hazelnuts, to someone who has never eaten them before? You really can't do it other than by comparing them to other foods known to the person.

But I'll take a shot at adumbrating what Santa Teresa cheese is like. Soft, slightly sharp with a mild milky flavor. Maybe. Whatever. And it's not bad. I think that's the key phrase. It's not bad.

Egg brooding in land snails

Kuźnik-Kowalska, E., Pokryszko, B.M. (2007). Incipient parental care in Discus - A plesiomorphic state of a truly endodontid character? Journal of Conchology, 39(4), 467-468.

The distribution of the land snail genus Discus, whose shells have wide umbilici, ranges across Asia, Europe and North America. Discus and the North American endemic genus Anguispira are placed in the family Discidae, although some authors may place them in the much larger family Endodontidae of the Pacific Islands, New Zealand and Australia. One interesting behavioral characteristic of the Pacific Island endodontids is the use of the shell's umbilicus as an egg brood chamber (see, for example, Solem & Climo, 1985).

In this paper, Kuźnik-Kowalska and Pokryszko are presenting evidence that 3 European Discus species may also use the umbilici of their shells to transport and brood their eggs. They observed that after a snail lays a batch of 1 to 6 eggs, it crawls over them to cover them with mucus and during that process eggs sometimes enter and stick to the umbilicus of the snail's shell. However, this happened at a rather low rate, about 28% of the time in D. ruderatus and about 7-8% of the time in D. rotundatus and D. perspectivus. Also, in only a few cases were the eggs carried until they hatched. The 2 photographs in the paper are unfortunately of poor quality and do not provide clear details.

The authors suggest that what they observed may be the ancestral (plesiomorphic) state of a character that evolved further in the Pacific endodontids. Until further data become available, it is not clear to me that the described phenomenon in Discus is an adaptive behavior. The outcome rather seems to be an incidental result of the snails' habit of crawling over its own eggs. But then again, that may be how all behavioral adaptations start out.

What would be the adaptive value to a snail the brooding of its eggs in the umbilicus of its shell? The authors suggest that this may protect the eggs against predation, desiccation and cannibalism by their siblings. But egg cannibalism can still take place if more than one egg is present in a snail's umbilicus and the first snail that hatches eats the other eggs. Moreover, egg cannibalism may not be a bad thing at all for the lucky few who get to hatch first. Baur (1992) noted that 67% of the hatchlings of Arianta arbustorum that cannibalized unhatched eggs became adults compared to 38% of those that ate only lettuce.

Forget the salad, I am having eggs for dinner.


Baur, B. 1992. Cannibalism in gastropods. In Elgar, M. A. & Crespi, B. J. (eds.) Cannibalism: Ecology and Evolution among Diverse Taxa. Oxford University Press.
Solem, A. & Climo, F.M. 1985. Malacologia 26:1-30.

Slugs in February

Yesterday and today have been unseasonably warm. This afternoon around 2 o'clock, the temperature at the Baltimore-Washington International Airport was reported as 22 °C (72 °F). Starting tonite, it is supposed to cool off again.

Last nite around 7:45, the temperature in my backyard was 10 °C and the ground was wet from an earlier rain. Perhaps not too surprisingly, slugs were out on the rocks. There were several Deroceras reticulatum. It looked like this one was helping itself some dead leaves.

Isopods were out on the rocks too. But as soon as the light from my flashlight fell on them, they would scamper away into dark corners. One of them, however, crossed paths with a Deroceras and instead of getting out of the way, it just stood there allowing the slug to crawl over it. Perhaps a little bit of slug slime was just what it needed.


Then there was this large dark brown slug, probably an Arion subfuscus, on the ground. Limax maximus, which are quite common on summer evenings, were conspicuously absent. Perhaps they remain dormant throughout the winter regardless of the weather. I will go out again tonite to check things out before the winter returns tomorrow.

What's in the news

An insect, Orectochilus orbisonorum, has been named after the late Roy Orbison and his widow Barbara.

Guardian reports that the rats that may have swum ashore from the Spinningdale, a ship that hit rocks off the archipelago of St. Kilda last week, may threaten the birds on the island.

According to the New York Times, double-dipping a la George Costanza of Seinfeld fame, may indeed spread bacteria.

A new study, reported in a recent Denver Post article, found that collisions with wildlife on highways have increased.


**********Breaking News!*******************Breaking News!*********

Deer poop spotted near suburban parking lot.

A yellow isopod

The common isopod Armadillidium nasatum, shown in the photo above, is ordinarily grayish-brown in color. Yesterday, taking advantage of the warmer weather, I went out in the backyard to see how the creatures under the rocks were coming along. Among the assorted slugs, earthworms, millipedes and isopods, there were 2 yellow isopods under 2 separate rocks.


I photographed them and took one of the specimens. They were easy to identify as A. nasatum from the prominent projection on their heads (arrow), a characteristic of the species. When disturbed, they roll up into a ball (not every terrestrial isopod species can do that).


I also e-mailed photographs of the yellow isopods to my usual isopod contacts, Joan Jass in Milwaukee and Ferenc Vilisics in Budapest. They have since informed me that such yellowish color morphs are occasionally seen in A. nasatum populations.

Sexologist of snails

Kabat , A.R., Petit , R.E. (2007). Glenn Robert Webb (1918-1999), his molluscan taxa, and his journal Gastropodia (1952-1994). Zootaxa, 1589: 1-21.

I never met Glenn R. Webb, but I have an almost complete photocopied set of his self-published malacology journal Gastropodia. His biography by Kabat and Petit finally put a real person behind what had been just a name to me.

Webb, a naturalist from his childhood, appears to have taken up malacology in his late teens when he and his family lived in Indiana. He served in the U.S. Army near the end of World War II. He was allowed to continue to practice malacology while stationed in France, where he kept more than 30 containers of live gastropods under his bed. Upon returning to the States, Webb worked at various jobs, frequently moving around. He didn't receive his Ph.D., from the University of Oklahoma, until he was 42.

Webb's lifelong passion was the study of the mating anatomies of land snails, to which he referred as sexological studies. In 1952, he started publishing Gastropodia; the 1st paper in the 1st issue was titled: "Pulmonata, Xanthonycidae: comparative sexological studies of the North American land-snail, Monadenia fidelis (Gray) – a seeming ally of Mexican helicoids." A total of 13 issues of Gastropodia came out at irregular intervals until 1994. All but about 7 of the articles were written by Webb. One annoying habit of Webb as the editor was his tendency to leave the last paper of an issue incomplete to be continued in the next issue. But because he didn't publish Gastropodia on a regular schedule, sometimes years would pass before a paper would be completed. The layout of the journal was also rather disorganized and his papers frequently compiled notes about many different species, turning indexing into a nightmare. The chronological list of all the papers published in Gastropodia prepared by Kabat and Petit will make life a bit easier.

Webb was a professor at Kutztown University, Pennsylvania between 1963 and 1985. He and his wife moved to Conway, South Carolina in 1996. He was apparently building a private laboratory to continue his studies at age 80 when he died.

Webb's personality and private life, perhaps intentionally, were left out of this biography; there is only a passing reference to his "brash iconoclasm, and lack of interest in confronting to social norms." A little more of the real person wouldn't have hurt.

Webb's legacy will live on for many years. A recent paper by Davison & Mordan* ends with this acknowledgement: "We would like to thank Glenn Webb for making so many observations over so many years. This paper would not have been possible without his contribution."

Unfortunately, the Zootaxa paper is not open access except for the 1st page. After I learned about the paper yesterday, I e-mailed Alan Kabat, who promptly sent me a pdf copy of it. I thank him again.


*Davison, A. & Mordan, P. (2007): A literature database on the mating behavior of stylommatophoran land snails and slugs. American Malacological Bulletin 23:173-181.