30 March 2006

Adventures in Beringia

Beringia is the land connection that existed between Alaska and the northeastern Asia during the last ice ages when the global sea level was more than 100 m lower than its present level. It was because of Beringia that the same species of animals and plants now live on both sides of the Bering Sea and that the ancestors of Native Americans were able to migrate from Asia to North America. The past land connections between North America and Asia interest me, because some species of land snails, for example, Zoogenetes harpa, may have used such bridges to migrate between the 2 continents.

brng2The last giant of Beringia, by Dan O’Neill, is about the scientists who have studied Beringia and how they have put together the pieces of the puzzle to develop our current knowledge of this very interesting part of the earth. Actually, the title refers to one particular person, the geologist Dave Hopkins (1921-2001), who devoted his life to the study of the Holocene geology of Alaska. There are also almost entire chapters about others, including the Swedish botanist Eric Hultén and the American archeologist Louis Giddings. The accounts of their field trips are all fascinating, but I wish the overall story was presented more coherently. Many others entered and left the story, often making me forget about Hopkins. The couple of chapters on Native Americans at the end could also have been left out. The origins of Native Americans, a fascinating subject on its own, and although closely tied in with Beringia, doesn’t quite fit into this book.

Nevertheless, I did learn quite a bit from this book. And although it is for the general readers, the book ends with a long list of references to the scientific literature that would be very helpful for those interested in learning more.

The Bering Land Bridge National Preserve is now on my list of places to visit, if I can only figure out how to get there.

29 March 2006

Is it a Helix? Is it a Lymnaea? Or is it both?

The shell on the left belongs to the freshwater snail Lymnaea stagnalis, while the one on the right is that of Helix aspersa, a land snail. And here is what you would get if you could put the two together.

I found this specimen in the land snail collection of the Smithsonian's Museum of Natural History. Tim Pearce and I examined it briefly. We came up with 3 explanations as to how it may have been created.

1. It is a fake. If it is a fake, it is a very cleverly made one. As you can see in the picture below, the body whorl of Helix grew over the body whorl of Lymnaea. To be able to do that one would have to remove the body whorl of a Helix shell by cutting along the suture of the body whorl, put the rest of the shell inside a larger Lymnaea shell, place the body whorl of Helix on the outside and, finally, glue everything together without leaving any traces of the cuts and breaks.

2. Tim suggested that a juvenile H. aspersa in its shell was purposely lodged, or glued, inside an empty L. stagnalis shell. The Helix couldn't get out, so it grew out of the Lymnaea shell.

3. I thought that a H. aspersa was removed from its shell and placed inside an empty L. stagnalis shell. Somehow, it survived, reattached its columellar muscle and continued to grow, building its own shell. In Tucker Abbott's Compendium of Landshells (p. 193) there is a picture a similar chimera of H. aspersa. According to Abbott, in that case "an aspersa animal was placed in an empty Ennea shell and became atttached."

X-raying the shell would help pick between the alternatives 2 and 3. An X-ray photograph could even reveal hidden cracks and expose the specimen as a fake. All I could do at the museum was hold the shell against a light, but that wasn't helpful.

Note that the bands on the Helix shell are visible thru the translucent Lymnaea shell near the lip of the latter. This is explained (if the whole thing is not a fake) by the fact that when a snail resumes growth after a break, the new shell starts growing below the old shell and slightly behind the break. I have discussed this with examples in 2 previous posts (here and here).

I am not familiar with the name, Cailliaud, on the label. The only Cailliaud in 2,400 Years of Malacology is Frédéric de Nantes Cailliaud (1787-1869). If this specimen indeed belonged to him, then it is from before 1870. Cailliaud might have written about this specimen or others like it. I will appreciate any further information, including literature citations, that anyone might have on Cailliaud's work with chimeras.

28 March 2006

Definitely an elfin


This little butterfly is either the Frosted Elfin (Callophrys irus) or Henry's Elfin (Callophrys henrici). I am leaning towards the former species.

I photographed it in College Park, Maryland around noon today. Because of its diminutive size, when I first saw it I thought it was a moth. The picture below will give you an idea of its size relative to the leaves and the grass blades.


Adult Frosted Elfins are around in the spring for a rather short period of 2 months or so. This is the first time I have photographed this species. Hopefully, the next time the pictures will be better.

27 March 2006

Intricacies of shell repair 2

Yesterday's post on shell repair explained that when a snail resumes shell growth following a break, new shell starts growing below the old shell and slightly behind the break. This was first shown to be case in Helix pomatia by Pollard et al.1

Diagrammatic representation of a growth break in a juvenile Helix pomatia. Top is the outside, bottom is the inside of the shell. Note how the new shell grew out from under the old shell as in model C in yesterday's post. Scale bar is 1 mm. Scanned from Pollard et al.1

Here is a real-life example that I photographed tonite. This is a fragment from a Helix lucorum shell, where there is a long break going from the top to the bottom (blue arrow). This seems to represent a growth stop rather than an injury to the shell.


Below is a highly magnified picture of the edge of the shell taken from the direction indicated by the red arrow in the picture above. The blue arrow marks the end of the break. The snail's body was along the bottom edge of the shell. The orange arrows are pointing at the long oblique overlap between the old shell (top and right) and new shell (bottom and left). Compare this picture with the diagram above.

The thickness of the shell along the photographed edge was variable; below the break it was ~0.2 mm and increased to ~0.34 mm towards the right. For the curious, I took the picture with an Olympus E-500 camera thru an Olympus SZ60 stereomicroscope.

1. Pollard, E., Cooke, A.S. & Welch, J.M. The use of shell features in age determination of juvenile and adult Roman snails Helix pomatia. J. Zool., 183:269-279, 1977.

26 March 2006

Intricacies of shell repair 1

A snail can start repairing a break in its shell one of 3 possible ways (see below): (A) New shell starts growing next to the old shell; (B) New shell starts growing above the old shell and slightly behind the break; (C) New shell starts growing below the old shell and slightly behind the break.

The red arrow points at a break in the shell; the blue arrow shows the direction of shell growth in all 3 cases. Darker brown represents old shell, lighter brown new shell. The snail's body is on the concave side of the shell.

Model B would require the mantle to flip backward around the edge of the shell. This may not be anatomically possible in pulmonate land snails. Model A would be the most economical one, because it would require the least amount of material, but to prevent the shell from falling apart, it would also require a very strong adhesion between the old and new shell edges. Note that in models B and C adhesion between the old and new shell is provided by the overlapping sections.

Pollard et al.1 showed that after a growth break in Helix pomatia, new shell grew according to model C. This is probably true for all pulmonate land snails. Below is a picture showing a long break in an Anguispira fergusoni shell. The shell on the left side of the break is "new" growth, while the shell on the right side of the break is "old" growth. Note how the new shell grew out from under the old shell as in model C above.

The aperture is on the right. The blue arrow shows the direction of shell growth.

The second post in this series is here.

1. Pollard, E., Cooke, A.S. & Welch, J.M. The use of shell features in age determination of juvenile and adult Roman snails Helix pomatia. J. Zool., 183:269-279, 1977.

24 March 2006

Winter survival of Vertigo pygmaea

Back in the fall of last year, I wrote about the tiny snails Vertigo pygmaea that live in my backyard. In November 2005, I collected 54 adults. After I measured them, I marked the shells of 11 of them with permanent ink and released all in the same area of my yard.

Yesterday I searched again in the same location and found 25 adults and 5 juveniles. After I brought them in and wetted them, they all revived. Five of the adults were marked. This indicated that at least some of the snails that were adults in November survived the winter.

The marked snails were under the same rocks were I had placed them in November. This suggests that they either tend to stay on the same rock or that they hadn't moved around much during the winter. Before I released them today, I marked 10 more. Later this spring I will do another collection to determine how far they will have dispersed.

In an another post, I remarked about the differences between the epiphragm of snails from California and Maryland. At least some snails in California make relatively hard calcareous epiphragms to block their apertures when they are dormant for long periods, while the eastern snails make only membranous epiphragms. Almost all Vertigo I found yesterday had fragments of membrane-like dried slime around their apertures. The slime they secrete as they are becoming dormant not only seals their apertures, but also attaches them to the rocks. When they are removed from the rock, the seal is broken and only the fragments remain. The snail pictured below still had its epiphragm intact, which was actually transparent, but in the picture reflected light makes it look shiny. (The scale was in millimeters.)


23 March 2006

Tomb robbery: a career not for the squeamish


If I had lived, say, about 2000 years ago, I would like to have been a tomb robber. Think about it. It was an "occupation" full of excitement, danger, instant riches. Every grave opened would have been a journey into an unknown with gold, silver, lapis lazuli at the destination, not to mention a skull or two. There is more. I would have been my own boss, although it would have been good to have an accomplice, the hours would have been flexible, although I suspect, most of the work would have been carried out at nite. There would also have been some commuting, mostly over rough territory. But, hey, no job is perfect.

Furthermore, a certain amount of "library research", which I am good at, would have been necessary to figure out where there were unopened graves that might have belonged to the royalty or otherwise, rich people. It would have been necessary to employ some middlemen to gather information and also to sell the bounty. We are talking about a regular business here.

So, if time travel ever becomes a reality, you know what I'll be doing.

But, it wasn't me who opened the graves in the picture. They were like that when I got there back in the summer of 2000. I took the picture near the ruins of Notium (Notion), an Aeolian city by the Aegean Sea northwest of Ephesus in western Turkey. It was a great place to visit, away from the beaten paths, lonely, forgotten, without signs, restorations, guides or anyone else. It was all up to my imagination to visualize the place the way it might have been a long time ago.

22 March 2006

Gulf Fritillary


I photographed these mating Gulf Fritillaries (Agraulis vanillae) in J.N. "Ding" Darling National Wildlife Refuge on Sanibel Island, Florida last July. It is interesting to note that the wings of the mating butterflies are partially overlapping (another picture is here).

Compare the relative positions of the Gulf Fritillaries with those of the mating Eastern Tailed Blues (Everes comyntas) whose only the tips of their abdomens were touching.

The Gulf Fritillary is primarily a southern species; its range extends thru the southern United States into South America and the West Indies.

20 March 2006

Today's good word: periostracum


Periostracum is the thin membrane-like organic layer that covers the outer surfaces of the shells of many snails [from Greek peri, around + ostrakon, shell].

Wherever the soil is low in calcium carbonate, land snails usually obtain their calcium carbonate by eating empty snail shells. The upper picture shows a shell of Mesodon thyroidus, a common northeast U.S. land snail. After the snail died, a smaller snail crawled inside the empty shell and ate a section of the shell behind the lip, leaving behind the membranous periostracum, part of which is sticking out (arrows).

Periostracum is usually what gives shells their colors. Old shells are almost always white, because they have lost their periostraca. The shell below is that of Neohelix albolabris, another northeast U.S. forest snail. Its white shell underlying the periostracum is visible at places where the latter has disappeared.


One interesting property of calcium carbonate that makes up snail shells is that its solubility increases as water temperature goes down. Geerat Vermeij1 noted that many snails that inhabit cold waters have very thick periostraca that help protect the shell from dissolving.

1. Geerat Vermeij. 1993. A Natural History of Shells. Princeton University Press.

18 March 2006

I was there

Whenever I recognize a place in an aerial photograph, my usual response is, "Hey, I was there!" This is a photograph of one of those places, a small section of College Park, Maryland.


The creek near the middle is the Paint Branch, the CSX tracks are on the left, the Metro tracks are on the right. (North is towards the top.) Here is a close up of the spot where the tracks cross over the creek.


The aerial pictures, from Terra Server, were taken on 7 April 2002. Here is a shot I took about 10 days ago looking south between the 2 sets of tracks. I was standing just a few meters off the trail visible in the aerial pictures.


The fine sand that has accumulated along this creek is especially good for finding animal tracks. Some examples I have posted are here.

Critique of an old paper on Fossaria modicella

For the past 4 years or so, I have been monitoring the population structures of 2 colonies of Oxyloma retusa (family Succineidae) at a small local lake. Although O. retusa is a land snail, it always lives near the water, on mud and on cattails sometimes growing directly out of the water. In that sense, it comes close to being amphibious. The data I presented at the 2004 annual meeting of the American Malacological Society1 showed (if you believe my interpretation) that the snails were very short lived and that there were 2 generations per year. I still have not published my data, because I don’t quite know how to interpret the data in an evolutionarily meaningful way.

Earlier this week I was reading a paper that mentioned that the aquatic/amphibious pulmonate snail Fossaria modicella had 2 generations per year and cited a 1935 paper by Harley Van Cleave2 as the source of that information. Naturally, I got excited. I went to the library, got a copy of the paper and read it right away, hoping to extract from it some insight that would help me better understand my O. retusa data. However, I was to be disappointed.

In short, Van Cleave collected 10 samples (a total of 1793 individuals) of F. modicella in Indiana over 3 years, measured the shell length of each. From these data, he concluded that there were “two distinct broods per year, a spring generation in March and a summer generation in July or August.” Almost exactly the same situation as what I have found to be the case in O. retusa.

But, there are 3 problems with Van Cleave’s study. First, he collected live snails and does not appear to have returned them to the study site after he measured them. On some occasions, he removed relatively large numbers of live snails, for example, 178 on 2 April 1934, followed by 229 on 22 April. This is potentially problematic, because, unless the total population is so large that a few hundreds of specimens is a negligible quantity, one can not rule out the possibility that removal of large numbers of live snails could be affecting the growth and reproduction of the remaining snails. (To avoid this problem, I have always returned the live Oxyloma to my collection sites within a day.) Second, collections were done not to obtain a meaningful spread of the 10 samples over a year, but at somewhat haphazardly picked dates (during family vacations). As a result, 3 collections were done in April, 2 in October, but none in May or September. Furthermore, more than a month elapsed between the sampling dates in July and August when, according to the author, a new generation was emerging. Third, without first demonstrating that the annual generation cycle was temporally the same each year, Van Cleave pooled and analyzed the samples from 3 years together.

Here are his data plotted. To generate smoother curves, I decreased the number of size classes from 15 to 8.


The bottom line is that from this graph, and taking into account the problems with the study listed above, I am not convinced that F. modicella had 2 generations per year during the study period. What I see is that the generation that survives the winter matures during the summer. Their offspring (the snails less than about 3 mm in length) survive the winter to start the cycle over again next spring. So, there is only one generation per year.

I will keep working on my Oxyloma data.

1. Abstracts of the 2004 AMS meeting. Mine is on p. 63.
2. Van Cleave, H.J. 1935. The seasonal life history of an amphibious snail, Fossaria modicella, living on sandstone cliffs. Ecology 16:101-108.

16 March 2006

Common Checkered Skipper


chckrdskppr3There are only 2 Pyrgus species known from Maryland, the Grizzled Skipper (P. centaureae) and the Common Checkered Skipper (P. communis). I believe the butterflies in my photographs represent the latter species. The photos above and on the left are of the same individual, while the one below, photographed about a week later at the same location (end of September-beginning of October of last year), is a different individual, because the fringes of its hind wings are more complete than those of the earlier individual. The location was a highly disturbed open field near a large creek and a busy road (East-West Highway) in Riverdale, Prince George's Co., Maryland.


The range of the Common Checkered Skipper covers most of the temperate North America extending south to the mountains of northern Mexico. Apparently, the species cannot survive very cold winters. A few days ago Firefly Forest Blog had pictures of a male Common Checkered Skipper from Arizona.

In contrast, the Grizzled Skipper is a more widely distributed Holarctic species, whose range extends not only to Alaska, Labrador and the arctic Quebec, but also across Asia to northern Europe.

15 March 2006

2,400 Years of Malacology

2,400 Years of Malacology, by Coan, Kabat and Petit, is a "comprehensive catalog of biographical and bibliographical publications for over 7,000 malacologists, conchologists, paleontologists, and others with an interest in mollusks, from Aristotle to the present." The 3rd edition of this free electronic publication is available here.

The long introduction provides many links to sites with biographical information about malacologists. In addition, the 3 appendices provide citations to "(1) publications on oceanographic expeditions that resulted in the collection and description of mollusks; (2) histories of malacological institutions and organizations; and (3) histories and dates of publication of malacological journals and journals that are frequently cited in malacological publications."

14 March 2006

Still crawling strong


This is a promotional flyer for the malacology journal Nautilus from the 1890s. At that time the editor was Henry Pilsbry. The Nautilus, now edited by Dr. José H. Leal, has been in publication continuously since 1886.

José, who provided a scan of the flier, is also the director of the one of a kind Bailey-Matthews Shell Museum in Sanibel, Florida.

12 March 2006

Always carry a Hungarian in your car

Recently photographed at Dupont Circle in Washington, D.C.

11 March 2006

First butterfly picture of the year


Spring is definitely here. Today was a beautiful day, mostly sunny and warm. I had my first glimpse of a butterfly this morning. It was high above my backyard, but it disappeared as quickly as it had appeared.

Early in the afternoon, I went out for a walk in Black Hill Regional Park near my house here in Germantown, Maryland. First, I saw a moth. I got all excited. But, as I was approaching it with the camera, it flew away. I grabbed my gear and climbed up a hill. At the top, I saw a butterfly, and then another one and then another one. I spent about 40 minutes photographing them. Luckily, they had no intention of leaving the area.

I am identifying it as the Eastern Comma (Polygonia comma), although I can't quite figure out the difference between the Eastern Comma and the Green Comma (Polygonia faunus). However, I note that the latter species has not been recorded from Maryland. (The checklist of Maryland butterflies is here.)

What does the adult Polygonia comma eat? There are no flowers or rotting fruits around yet. Actually, the butterflies didn't look like they were looking for food. They were either basking in the sun on the dry leaves or circling around each other.

10 March 2006

Friday nite's beer review: Kingfisher from India New York

kngfshrA few years ago I was at an Indian restaurant with some friends. We asked the waiter if they served Indian beer. He proudly declared that they had Kingfisher. And then, as we were each ordering a bottle, he added "But, it is brewed in New York."

This is that well-known Indian lager beer, bought at a local store, and indeed, brewed in Saratoga Springs, New York. Nevertheless, regardless of where it comes from, Kingfisher is a pretty good beer. It has a light, mild flavor with a very slight sweet taste. I will be drinking it again.

I am disappointed, though, that the company’s flashy website offers very little information regarding the different beers they say they manufacture. If you have time to waste, however, you may want to look at the Kingfisher swimsuit calendar.

Index to the Snail's Tales' Beer Reviews

09 March 2006

Hey buddy, are you done in there?


This is what the waiting line looked like outside the men’s room at the Delaware Museum of Natural History last Saturday.

I took this picture in the collections area that is normally closed to the public, but there are plenty of other wonderful things to see elsewhere in the museum. Next time you are in Wilmington, Delaware, set aside some time to visit DMNH. You won't regret it.

08 March 2006

Wrist-walking humans

wrstwlkrA case study1 of five siblings who are wrist-walkers has come to my attention. The individuals (4 females, 1 male), all adults from a village in southern Turkey, have never developed bipedalism; instead, they walk and run on their feet and wrists with palms, but not the fingers, contacting the ground. According to the study, they all have a congenital brain condition and are mentally retarded. Interestingly, another sibling with the same cerebral symptoms walks upright.

There are 2 unfortunate aspects of the story. First, the authors report that these individuals, although accepted by their family, are teased and laughed at by the other villagers. Second, they don’t appear to have received any form of physical therapy that might have helped them develop bipedal walking.

At the end of the paper, there is a brief discussion of the evolutionary implications of this particular case. The authors mention that wrist-walking might have been an intermediate stage during the evolution of bipedalism from quadrupedalism. And then, they go on to speculate that "in these modern human quadrupeds, we are indeed seeing the 'rediscovery' of something very like the quadrupedal gait used by our ancestors." Well, I don’t think I would go that far based on one case. To me, this sounds more a like a case of infants with developmental problems imitating their older siblings to do the best they can in the absence of proper medical care and early intervention.

Note added later: Afarensis has posted a more detailed review of the subject.

1. Nicholas Humphrey, John R. Skoyles, Roger Keynes. 2005. Human Hand-Walkers: Five Siblings Who Never Stood Up. CPNSS Discussion Paper DP 77/05. pdf

07 March 2006

What does a train engine look like from high above?

A couple of posts ago STUFIT* had an aerial picture of a train downloaded from Terra Server. We had marked with an arrow what we believed were the engines.

However, Pascal at Research at a snail's pace disagreed with our identification of the engines. Now, we will demonstrate that we are right and he is wrong. (Hey, there is nothing personal here. We are doing this all in the name of science.)

Here are 2 indisputable engine photographs (left and center) that STUFIT found at the Union Station in D.C. (also from Terra Server) compared with the disputed photograph (right) from our earlier post. We have enlarged all 3 pictures and also rotated and flipped them so that they are all oriented more or less in the same direction with the sun shining from the left.


Pascal's objection to our identification, in the rightmost picture, of the 2 front "cars" as engines is that "in general, locomotive engines have distinct roof-top characteristcs [sic] that would stand out even in satellite view."

It is difficult to make out any structures on the roofs of the engines in the leftmost photo. But compare the engine in the middle photo with the front one in the rightmost picture. The yellow arrows mark the corresponding roof-top structures in the 2 sets of pictures.

We rest our case.

Revision added 8 March: Every monitor is different. When I looked at the leftmost picture on my home computer last nite all I could see was a featurless dark roof-top. But, now I am on a different computer and I can make out some structures.

While his guitar gently sweeps

George Harrison singing My Sweet Lord with Ringo at the drums.

My wife and I have enjoyed watching the recent DVD edition of The Concert for Bangladesh. The concert, on 1 August 1971, was organized by George Harrison to raise money for the starving people of Bangladesh and featured, besides George, Bob Dylan, Leon Russell, Ringo Starr, Ravi Shankar, Eric Clapton and many other musicians.

We especially enjoyed Harrison's While my guitar gently weeps with Clapton playing his famous solo, Bob Dylan's Just like a woman and the acoustic version of Harrison's Here comes the sun. Clapton was, otherwise, very low key and didn't sing any songs.

To my own surprise, however, I thought the most electrifying performance at the concert was Bangla Dhun, the opening piece that had fascinating "duels" between Ravi Shankar playing the sitar and Ali Akbar Khan playing the sarod. If I ever become a fan of Indian music, it will be because of that piece.

Harrison, Dylan and Russell singing Just like a woman.

In addition to the concert itself, the DVD also features previously unreleased songs from the rehearsals and the afternoon show as well as brief recent interviews with some of the musicians, including Ringo and Eric and other film clips related to the concert. There were also some amusing moments, including the scene during the performance of Something, when George Harrison forgets a line, mumbles something incomprehensible, then turns back and smiles, probably at Ringo, who while singing It don't come easy earlier had messed up one of his lines. The spontaneity and naturalness of the performances add to the pleasure of watching this concert.

According to The George Harrison Fund for UNICEF, the Concert for Bangladesh has raised for than $15 million for UNICEF. If you buy this DVD you will contribute towards a worthy cause (it's better than giving money to your church or any "faith-based" charity) and enjoy a wonderful concert. And you won't even have to wait in line for tickets.

06 March 2006

Lots of Liguus


Last Saturday I spent a couple of hours looking thru several lots of the tree snail Liguus fasciatus at the Delaware Museum of Natural History.

These snails are native to southern Florida, Cuba and Hispaniola. In the U.S. they are considered endangered. In a previous post I told the tale of how a couple of summers ago down in Florida I had to confront hordes of blood-thirsty mosquitos just to take a few pictures of Liguus. Luckily, mosquitos were not a concern at the museum.
The picture on the left shows a big guy from Holguin, Cuba. The museum label identified it as Liguus fasciatus achatinus.

I was specifically looking for scarred shells and I did find several. Below is an example of one specimen that suffered a long break while it was still a juvenile. The blue dotted line is the estimated location of where the lip was before it broke. The area bounded by the blue line and the jagged scar ending at the red arrow is the rebuilt portion of the shell.


The snail survived partly because it was able to withdraw behind the broken section. This specimen and a few others like it demonstrated to my satisfaction that Liguus fasciatus, like many other land snails, also build their shells larger than their bodies. I have discussed this topic before in this post.

05 March 2006

What does a train look like from high above?


Snail’s Tales’ Useless and Frivolous Information Team (STUFIT) proudly presents this photo of what undoubtedly is a train on railroad tracks (where else would a train be?) somewhere not too far from the Union Station in Washington, D.C. The red arrow I added points at the engines (there appear to be 2 of them).

Here is a closer look.


Here is a question for everyone. Is it possible to determine the direction of travel of a train from one aerial photograph only? Don't forget that the engine could push the train from behind while facing either way.

Aerial photos are from Terra Server.

In a future post, STUFIT will show you how to identify railroad tracks in aerial photos.

03 March 2006

Do their shells protect land snails against predators?

The shells of pulmonate land snails must offer some protection against their predators. After all, the shell is a hard solid structure that in most cases envelopes the entire snail and the aperture could be blocked by an epiphragm or by various folds and lamellae (here is an example).


However, large predators of snails, for example, mammals and birds, can easily break snail shells. The picture above shows some shells of Eobania vermiculata from Istanbul, Turkey. I found all of these shells at one location. All, except the one on the lower right hand corner, had similar breakage patterns indicating that the cause of breakage was the same in each case. The most likely predator was probably some rodent, a mouse or a rat.

Smaller predators, on the other hand, including carnivorous snails, enter the shell either through the aperture or by drilling thru it. The exact function of the folds and lamellae that commonly block the apertures of many species is actually not clear.

The picture below is of a shell of Albinaria caerulea (from near Ephesus, Turkey) with 2 bore holes that had been made by a larva of a Drilus beetle. Drilus larvae are common predators of land snails in Europe, Africa and the Middle East. But only in Greece, Turkey and the Middle East do they bore thru snail shells.


02 March 2006

I like my sponge raw

A post at Pinguicula regarding the utility of saving digital images as RAW files prompted me to do some tests. I take pictures of snail shells and other small objects very frequently under fluorescent lamps. Although, digital cameras, including my Olympus E-500, have preset white balance (WB) adjustments for various types of fluorescent lamps, I have never had satisfactory results using those. So, what's one to do?

Here are some test results. First, on the left is the test subject, good ol' Spongebob, photographed using E-500's built-in flash with WB set at Auto as recommended in the camera's manual. Spongebob was on a white card which was on a gray card visible along the right side. The resulting picture looks fine as far as the colors are concerned: white is white and gray is gray. However, I normally don't like to use flash when I am photographing shells because flash creates harsh shadows and I usually have difficulty getting the exposure right.

Below is Bob photographed under one my fluorescent desk lamps with WB set at Auto. The result is ugly: white is yellow, gray is yellowish-brown. Next to it is the same picture after I readjusted the color balance in Photoshop. There is some improvement, but it is still not satisfactory.


Next is a couple of pictures taken with the color temperature set at 4000 K and 3200 K. (This was done using the custom white balance function of Olympus.) You can see that as the color temperature goes down, the yellow cast is replaced with a greenish cast. (If the color temperature is increased, the redness of the picture increases.) So, setting the color temperature manually doesn't correct the colors either, although the picture taken at 3200K is preferable to that taken at Auto WB.


Finally, below is a picture taken with WB set at Auto, but saved as a RAW file. Using Olympus Master, the software that came with E-500, I readjusted the gray point by picking up the eyedropper tool and clicking on the part of the picture showing the "gray" card that was actually yellowish-brown as above. When the program finished its adjustment, the correct colors were miraculously restored to the picture.


The ability to correct the WB to such an extent is, therefore, one of the advantages of saving images as RAW files. Now I have to always remember to include a portion of a gray card in all pictures I take under fluorescent lights.

01 March 2006

Sculpture for a cold day


Post-Balzac by Judith Shea (1991) outside of the Hirshhorn Museum in D.C.