29 September 2010

Mercenaria mercenaria

These clam shells were abundant on the beach at Assateague Island last August. I am not versed in bivalve taxonomy, but I believe they are the valves of Mercenaria mercenaria. A characteristic of the species is said to be the purple border along the edge of its shell.

The shells of Mercenaria mercenaria are relatively large, thick and heavy. It is fascinating to ponder on the question of why the clam invests so much calcium, energy and time to build such a fortified pair of shells. Is the function of the shells mostly to protect their occupant from predators?

I collected several of these shells primarily for display. They are now sitting in a large glass bowl in my library. Obviously, they are also good for stimulating one's mind into thinking about evolution.

27 September 2010

Land snails of Turkey: Helix lucorum

The largest land snail in the Istanbul area of Turkey, and in fact in many other parts of Turkey, is Helix lucorum. Despite the ongoing loss of wildlife habitats to incessant development in Istanbul, several species of native snails have so far survived in cemeteries, small parks and hillsides that are too steep for the construction of buildings. Helix lucorum is one of the survivors. The species is surprisingly common in certain parts of Istanbul. Many of them can be seen crawling in gardens and along walls after rainstorms.

Helix lucorum is edible and in the past, when there were more Greeks in Istanbul and elsewhere in Turkey who eat snails, while the Moslems usually refrain from doing so, the species was much exploited. The British explorer archaeologist Charles Fellows in the journal1 of his travels in Turkey during the years 1838-1842 wrote that "a brown shell-fish, in form similar to a large snail, and larger than a pigeon's egg" was much eaten in Çanakkale along the Dardanelles. Upon arriving in Istanbul a few days later, he corrected his diagnosis:
I have said that the people here eat a kind of shell-fish like a snail: I find it is a snail, and not a native of the sea, although sold by the fish-dealers. This morning I saw a dozen hampers of them; the well-known tender-horned inhabitants were gently peeping forth, but an occasional shake given to the hamper made them retire into their shells; the large brown kind I have before mentioned is the most common, but the people here also eat the more delicate small ones; as they are not considered meat, they add to the limited fare of the Catholics during the fasts. It is now Lent, and hence the greater display of them in the streets. The snail found in the chalk-pits near Epsom, and said to have been introduced into England nearly a century ago for medicinal purposes, appears to me of precisely the same species*.

*Helix Pomatia.
The snail Fellows saw was probably Helix lucorum.

It seems that the poor snails, once eaten and now kicked out of their habitats, will never get a break from humans.

Here is an old post about the epiphragm of Helix lucorum.

1Travels and Researches in Asia Minor. Available in Google Books.

26 September 2010

I was going to disclose the meaning of life...

but due to feline interference, I have no choice but to postpone my revelations.

I apologize for leaving you in a quandary until further notice.

25 September 2010

Spot the woodpecker

This morning I was stalking the birds at the bird feeder with my color camera in hand (see below) when I thought I spotted something unusual on the trunk of the measly plum tree next to the feeder. It was a woodpecker. Can you find it in the picture below?

Here is a closer look at the center of the same picture. There is the woodpecker.

This was the only picture of it I could take before it flew away. It was either a hairy woodpecker (Picoides villosus) or a downy woodpecker (Picoides pubescens). Maybe a serious bird watcher, which I am not, can pinpoint the species.

As for color cameras, or rather, cameras loaded with color film, there was a time when they were rare and novelty items. Stalking birds with color camera was the name of a book I saw at the local public library's used book sale last month. Amazon, where many cheap copies are available, gives the date of the 1st edition as 1951. We have come a long way.

23 September 2010

Green-backed heron by the lake

These small herons are occasionally seen along the margins of lakes around here in Maryland. They are usually quite shy and fly away as soon as they spot someone approaching. This particular bird, however, which I photographed last August, was an exception. It allowed me to come quite close to it.

While I was photographing it I thought I saw it regurgitate something. It then re-swallowed the thing, which may have been a frog. Is this something they normally do?

If I am not mistaken it's a green-backed heron (Butorides striatus).

22 September 2010

More insignificant thoughts on statistical versus biological significance

Statistically significant data are not necessarily biologically significant. That premise was the topic of 2 previous posts (here and here). A paper I read today rekindled my interest in the subject.

Giovas et al. (2010) showed that the shell dimensions of the marine gastropod Strombus gibberulus (humped conch) increased over a period of 3000 years at a site called Chelechol ra Orrak in the Palauan archipelago. How much was the increase? The mean shell length increased 1.37 mm (~4% relative to the smallest sample mean) and the mean shell width increased 1.22 mm (~8% relative to the smallest sample mean).

Shell length histograms of Strombus gibberulus over 3 time periods, Early (3000-1700 BP*), Middle (1700-1000 BP) and Late (1000-0 BP). The increase in shell heights is barely noticeable. (Fig. 4 from Giovas et al., 2010.)

Strombus gibberulus is a relatively small snail: mean shells heights are ~32 mm, the mean shell widths are ~15 mm. The reported shell size increases were statistically significant. But were they also biologically significant? In other words, does a 4% to 8% increase in the mean shell dimensions of a population of a snail species over 3000 years increase the chances of survival and reproduction of the larger individuals? That's one question the authors of the study don't address. They do discuss 8 hypotheses as possible reasons for the observed increase in shell dimensions. These include possible changes in the foraging practices of the ancient human occupants of Chelechol ra Orrak who presumably ate the snails and changes in various environmental conditions of the site.

Small increases in snail shell dimensions may indeed have biological significance. We will continue to ruminate on this problem.

*Before the present

Christina M. Giovas, Scott M. Fitzpatrick, Meagan Clark, Mira Abed. 2010. Evidence for size increase in an exploited mollusc: humped conch (
Strombus gibberulus) at Chelechol ra Orrak, Palau from ca. 3000e0 BP. Journal of Archaeological Science 37:2788-2798.

21 September 2010

A tiger mosquito on my finger

This past summer we spent relatively little time in our backyard even during daytime. The reason was the over abundance and the incessant attacks of the Asian tiger mosquitos (Aedes albopictus). This particular individual survived a slap from my hand and regained enough of its posture to perch on the tip of my finger, but it was not "conscious" enough to attempt to feed on my blood.

The Asian tiger mosquitos were introduced to the U.S. from Asia several decades ago; their 1st record in Maryland dates from 1987. They tend to lay their eggs into small receptacles of water, natural or artificial. Discarded tires filled with rain water is a habitat they often use for breeding; which also appear to have been their primary means of passive dispersal throughout the world.

During the past few weeks we have had some respite from them, perhaps thanks to the lack of frequent rains.

Maybe I spoke too soon. One was flying around my face here in the living room a few minutes ago.

19 September 2010

Buckeye on the sidewalk

I encountered this butterfly during my after-lunch walk one day last week. It was flying around the sidewalk and often settling down either on the sidewalk or on the road only to be sent back in the air by every passing car.

I believe it is a common buckeye (Junonia coenia). This was the best and the closest picture I could get with my iPhone.

17 September 2010

Elisabeth and the snail

Elisabeth Tova Bailey, suffering from a debilitating chronic illness, once spent a bedridden year in the company a land snail. When she first received the snail from a friend as a gift in a pot of violets, she was bewildered:
Why, I wondered, would I enjoy a snail? What on earth would I do with it? I couldn't get out of bed to return it to the woods. It was not much interest, and if it was alive, the responsibility—especially for a snail, something so uncalled for—was overhelming.
Soon, however, the snail began to mesmerize Elisabeth and she was compelled to start learning about the snail and its kin not only from popular books but also from specialized publications. At the end, when she was well enough to return home, the snail had turned Elisabeth into a malacologist. And she understood that snails and the like are not to be ignored:
If life mattered to the snail and the snail mattered to me, it meant something in my life mattered, so I kept on...Snails may seem like tiny, even insignificant things compared to the wars going on around the world or a million other human problems, but they may well outlive our own species.
Elisabeth recounts the story of her illness and her snail companion in her little book, The Sound of a Wild Snail Eating, that came out just recently (Algonquin Books). There are many short chapters on snail biology, including one devoted to snail slime. Elisabeth even gives us her anecdotal data on snail homing (her snail, eventually identified as a Neohelix albolabris, often went on nightly forays to explore its surroundings and always returned to its pot), food preferences and parental care. The chapters often end with Elisabeth's reflections on her illness. I thought the transitions between malacology and personal affairs were sometimes awkward and hence the overall flow of the book was slightly choppy.

Nevertheless, this is an enjoyable read. It would be a good book for a long plane ride or a lazy summer vacation.

15 September 2010

A twilight cardinal at the feeder

We were eating dinner around 7:30 tonight when we noticed a bird at the feeder outside the kitchen window. It was already too dark to identify it. So I got my camera, put the 150 mm lens on it, jacked up the intensity of the flash and then put it right up against the window glass to prevent the light from bouncing back. Luckily, the bird stayed at the feeder while I was doing all of that. The following is the best picture I got.

The twilight feeder turned out to be a female cardinal, perhaps the one that was the subject of the previous post in this series.

14 September 2010

Land snails of Turkey: Euxina hetaera and Euxina circumdata

Euxina is a genus of land snails in the family Clausiliidae. The name of the genus, derived from Pontus Euxinus, the classical name name of the Black Sea, hints at the genus's distribution range mostly along the coasts of the Black Sea. Three species have been recorded in and around Istanbul, Turkey. Two of them, E. hetaera and E. circumdata, are among the snail subjects of a manuscript I have been working on.

The 2 species have similar shells that may be somewhat difficult to tell apart unless one has specimens of both available for comparison.

The shells of E. hetaera are usually larger than those of E. circumdata. The former also has denser ribs on the ventral side of the body whorl (above the aperture). These characteristics are obvious in the above picture where the pair on the left is E. circumdata and the one on the right is E. hetaera.

The 2 species seem to live in similar if not identical habitats and their colonies may sometimes be found near each other, although I don't know if I have ever found them together.

Here is a live E. circumdata. Note the length of the foot relative to that of the shell. That may be the subject of another post.

The previous entry in the land snails of Turkey series was Paramastus spratti.

12 September 2010

I think this is northern red oak

Tonight's mystery was the identity of this clump of oak leaves with one attached acorn that I picked up during this morning's walk in the nearby forest. I am not that good at identifying trees and the oaks, with about 15 possible species in this area, are one of the more difficult groups.

Using Frank Brockman's good ol' Important Trees of Eastern Forests (1968), I narrowed the identity of this specimen down to northern red oak (Quercus rubra), but I am not 100% positive about it.

Here is the acorn.

And here is a close-up of a leaf.

Incidentally, the background in the last picture is the proof for an upcoming paper of mine on the snail Pedipes ovalis. It is scheduled to come out later in the fall. I will write more about it then.

11 September 2010

A rainbow seemingly within reach

I spotted this almost ground level rainbow in the park near my house a few days ago. There was a fire truck nearby that was squirting a tall column of water into the air (for what purpose, I don't know). The water was falling into the lake in the form of a fine mist visible as a white cloud in the picture. The rainbow had formed in the mist right above the lake below the grassy slope.

As I was getting my companion positioned in the scene to get a photo of her with the rainbow, the firefighters shut off the water and the rainbow was no more.

09 September 2010

A shaggy cardinal at the feeder

This funny looking female cardinal (cardinalis cardinalis) was at the feeder about a week ago. Why did its feathers look so unkempt? It may have been a fledgeling who hadn't yet learned the fine art of preening.

The previous bird at the feeder was some sort of finch.

08 September 2010

Cunningham slugs

A couple of weeks ago we visited Cunningham Falls State Park near Frederick, Maryland. When during a hike I stopped to look at a trail sign, I noticed some peculiar marks on the back of the sign on the other side of the post.

It didn't take too long to recognize them as the feeding tracks of slugs. Here is a close-up.

The brownish layer covering the back of the sign is apparently some sort of algae (cyanobacteria), which slugs like to eat. You can see the marks left by the individual teeth of the radulae of at least 2 slugs, one large and one small.

This post was also about slug feeding tracks.

07 September 2010

03 September 2010

An encounter with a horseshoe crab

We came upon a live horseshoe crab (Limulus polyphemus) stranded on the beach last week on Assateague Island. It had gotten stuck in the sand sideways and could not right itself up. The crab was lucky that birds or kids had not yet noticed its legs flailing in the air hopelessly.

After I turned it over, it started crawling awkwardly with its multiple appendages leaving behind shallow scratch marks in the sand.

At the rate it was travelling it would have taken the crab quite some time to reach the safety of the water. So I decided to interfere. After posing with it for a few shots, I released it in the surf. It didn't resurface.

01 September 2010

Snail homing

Do land snails and slugs home? In other words, do they use the same feeding or resting spots repeatedly, day after day?

The idea that terrestrial gastropods, especially the more familiar larger ones, such as the snail Helix aspersa or the slug Limax maximus, home has been around for more than a century. These early claims of snail homing were almost invariably based on anecdotal or circumstantial evidence. For example, Taylor included the following statement in his Monograph of the land & freshwater Mollusca of the British Isles (1894-1900, volume 1, p. 312).

Helix aspersa is particularly noticeable for its love of home and for the exertions it will make to regain its shelter, having been observed to traverse with great labour broad dusty roads or climb rough walls to reach some favourite food, and when satiated not retiring at daybreak to the shelter of any convenient crevice, as might be supposed, but almost invariably retracing its often toilsome and arduous way to reach its favourite shelter, a peculiarity that has been verified by many observers on numerous occasions.
Note that Taylor didn't bother to give citations for the independent verification by the readers of the "numerous" demonstrations of snail homing.

Back in October 2008 when I was in Turkey, one of the urban parks near where I was staying had plenty of Eobania vermiculata. On a particular day, I noticed that many of those snails had become dormant on the walls surrounding the park. So I decided to carry out a little experiment to determine if Eobania vermiculata had a homing instinct. I numbered the shells of several snails and their locations on the wall. The idea was to see if they would return to the same spot after foraging for food, presumably during the night. The next day when I returned, I found some of the snails missing and some still dormant although not at the exact spots where they had been marked, but near them. Initially, I thought this demonstrated that some snails were indeed homing. Then I realized that my procedure was flawed, because I had no way of knowing if the snails had left their resting spots, foraged and then returned to the same spots or if they had simply moved a few centimeters away before becoming dormant again. One day I will carry out a better planned experiment.

Homing or not homing? The previous afternoon when I marked this snail, it was within the black circle; the next morning it was outside the circle. But how far had it travelled before becoming dormant again?

A few days ago it came to my attention* that a public experiment to test snail homing had been initiated in the U.K. and it was in fact about to end. I'm eager to learn their results.

*I thank my regular reader Joan Jass for sending me the link to this news item.