29 September 2011

Measuring diameters of tall shells

There are 2 basic shapes of snail shells: tall shells and wide shells. It is easier to measure the height (length) of a tall shell than it is to measure its width (diameter). The reverse holds for wide shells. In other words, because of their uneven shapes, the longest dimension of a shell is always easier to measure than the shorter ones.

The "standard" diameter of a tall shell is measured perpendicular to the coiling axis, also known as the columella (the white line in the picture) of the shell.

But this requires that the columella be held parallel to the caliper jaws. Easier said than done. To take the above picture, I had to support the shell with plasticine.

Some years ago, I realized that it was much easier to measure the oblique diameter of a shell. Here is one way of measuring the oblique diameter*. Note that the columella is not parallel to the caliper jaws.

The 2 diameters are, of course, not equal to each other. The perpendicular diameter of the shell in the pictures was 5.8 mm, while its oblique diameter was 5.5 mm.

The shell in the pictures is Batillaria minima, the subject of 2 manuscripts I am currently writing.

*I showed another way of measuring the oblique diameter in this post. It is imperative that the measurement method be explained in a manuscript so as not to leave any uncertainty.

25 September 2011

The native and the alien

Back in 2006, for a brief period I kept an individual of the native philomycid slug Philomycus carolinianus and an individual of the introduced slug Arion subfuscus in captivity. The slugs lived in the same container and as far as I could tell, their interactions were peaceful. I published my observations as a short note in the 2007 issue of Tentacle (p. 14).

About a week ago, I made a similar observation, this time in the wild. I was searching for Megapallifera mutabilis, another philomycid slug. I found one squeezed inside a tight crevice in a tree and there was an Arion subfuscus a few centimeters below it.

If the 2 species had antagonistic interactions, they probably wouldn't rest so close to each other. Or would they?

21 September 2011

One more well hidden tree frog

A gray treefrog, Hyla versicolor or H. chrysoscelis, in the cavity of a tulip poplar.

The previous well hidden tree frog post was here.

19 September 2011

Snails of an Ottoman fort

Back in July 2010 when we were in Turkey, we spent one afternoon visiting the ruins of an Ottoman fort in the village of Rumelifeneri at the entrance of the Bosphorus from the Black Sea.

The main purpose of our trip to the site was, of course, to collect land snails. The paper presenting the results of our little survey just came out in Triton. You may download a pdf version of it from here.

The snail fauna of the location was impoverished in terms of the number of species, although the shells of the existing snails were abundant. The most noteworthy find was the 2nd ever record of Discus rotundatus from Turkey.

16 September 2011

A pickup for slugs

Last Sunday we took a walk along a wooded park in a slightly rural area. Near the end of the park there were some isolated houses and in front of one of them was an old, dirty pickup truck.

I noticed some peculiar marks on the dust-covered hood of the truck.

On close inspection, they turned out to be slug feeding tracks.

These slugs normally graze on layers of blue-green algae (cyanobacteria, actually). But what was covering the hood of the truck didn't look anything like algae to me. It was for like a blackened crust of street dust. There must be something nourishing in it, though.

Here is another post about the discovery of slug tracks in an unexpected spot.

13 September 2011

But was I art?

Back in July when we were in Pittsburgh for the American Malacological Society's annual meeting, my wife and I also visited Wood Street Galleries. There was an exhibit called "Long are the Days, Short are the Nights" featuring a group of artists from Iceland, the country that insists on slaughtering whales.

There were some intriguing pieces, including this one called Rotating Unit by Egill Saebjörnsson.


It consisted of a rotating piece of chicken wire thru which patterns of light were being projected on the nearby wall.

I couldn't resist the temptation to include myself in the display.

Maybe that's the whole point of art.

11 September 2011

Asian tiger mosquito caught on film

Prior to the early 20th century, there had been many deadly epidemics of the virus-caused illness yellow fever in the Americas. In 1881, the Cuban doctor Carlos Finlay proposed that the disease was transmitted by mosquitos. To establish that mosquits were indeed the vector of yellow fever, the American army surgeon Walter Reed carried out experiments with human volunteers in 1901. The volunteers allowed themselves to be bitten by mosquitos that had previously fed on yellow fever patients. Some of the volunteers contracted yellow fever and died from it.

I don't think I would ever volunteer for such a heroic act. Nevertheless, yesterday I allowed an Asian tiger mosquito to feed on my arm for more than 30 seconds so that I could film it. Here is a 10-s clip for your enjoyment.


Not much happens actually. It would be more interesting to catch a mosquito in the act of inserting its proboscis thru the skin. But that would probably require quite a bit of luck, many trials of filming and not to mention very cooperative volunteers.

Sorry for the shakiness of the clip; it was difficult to hold the camera steady with 1 hand at the high magnification I was using.

08 September 2011

A new website for alien gastropods in North America

The United States Department of Agriculture's Animal and Plant Health Inspection Service has just made public Terrestrial Mollusc Tool for those terrestrial gastropods that are likely to be introduced into the U.S. from foreign countries.

The primary users of the tool are intended to be customs inspectors at U.S. ports of entry whose duties include the spotting and the identification of live snails and slugs that may be intentionally or unintentionally being brought into the U.S. These include the pest species such as the giant African snails (Achatina spp.). But the key should be useful to everyone who is attempting to identify the non-native gastropods, for example, Cepaea nemoralis, already established in North America.

The tool also provides useful information on the biology and study of gastropods, including well-illustrated instructions for dissecting snails and slugs.

As mentioned in the Acknowledgements, yours truly was one of the "expert" reviewers of the beta version of Terrestrial Mollusc Tool.

07 September 2011

2 clueless trees

This beech (left) and the tulip poplar next to it have obviously not heard of the dictum that species are supposed to compete with each other. This picture doesn't reveal that they are both about equally tall and, so far as I can tell, equally healthy. That they have grown so well so far is an indication that they are actually tolerating each other.

Then again, maybe they are in a fierce competition. It's hard to tell what's going on high up in the intertwined canopy or deep among the tangled roots.

05 September 2011

Weekend gastropods

The warm and humid weather over the weekend had brought the slugs out. On Saturday morning, I was able to collect 20 Megapallifera mutabilis in an hour. I brought them home and weighed them to add more data to the population cycle project that has been going on for 2.5 years (more info here).

These slugs have a tendency to aggregate both in the wild and in captivity. This is called huddling.

During our Sunday morning walk, I returned the slugs unharmed to their favorite trees. My wife and I then walked to a spot where 2 days earlier we had collected about a dozen shells of the snail Neohelix albolabris. We searched for about a half an hour and found another dozen or so. We did not see any live snails, but I found one that had died recently. The snail's body was still intact and it hadn't started to smell yet. So I brought it home and saved it in alcohol.

That was the 2nd population of Neohelix albolabris in the park near our house that we have come across this year. I wrote about the 1st one here.

03 September 2011

Methylene blue

01 September 2011

An ancient surface

This is a close-up of a fossil bivalve shell from the famous Calvert Cliffs of Maryland. It is probably a Chesapecten sp., maybe about 5 million years old.