Within about a half hour period around noon today, I saw 5 of these slugs crawling on a dry sidewalk. One slug had already run out of steam, or rather, liquid water, in the middle of the sidewalk and was rapidly approaching its demise. I relocated it to the grass along with the other 4 who were totally oblivious to the risks of crawling on bone dry concrete.
They were about 2 to 2.5 cm long and black. Very Black. I had to lighten up the pictures in Photoshop considerably to make their skin features visible. I believe they were Deroceras laeve.
I am continuing to loot the Royal Society. One of the more interesting gems of today's session was an extract of a letter published in the Philosophical Transactions in 1668. It was from an Italian scientist, Giornale de Letterati, who described a microscope of a "new fashion" that had been constructed by another Italian, Eustachio Divini.
Here is the description of a session with Divini's microscope:
What could this Atome of Animals have been? Unfortunately the letter doesn't indicate if the sand they were watching was dry or wet. Since the animal had many feet, it was most likely an arthropod of some sort. However, if the sample was from an aquatic habitat, the animal could have been a tardigrade, but I don't think tardigrades have white and scaly backs. The tiny animal was probably real, but we need to keep in mind that many details the early microscopists thought they saw may have been optical artifacts created by their imperfect instruments.
Back in 1952, someone named William B. DeWitt, who may have been a parasitologist, wrote a paper about where he had found the snail Pomatiopsis lapidaria around Washington, D.C. Of the 3 locations he gave, all of which were along the Potomac River, one was a place he called "Fletcher's Boat House about two and one-half miles upstream from Key Bridge".
Early last week, when I re-read DeWitt's paper, it dawned on me that "Fletcher's Boat House" was the same place as Fletcher's Cove within the C&O Canal Park and which place I had passed by several times since last summer. There is indeed a boat house there for renting boats (not the house visible in the picture below).
Last Friday I visited Fletcher's Cove and after about a 20-minute search and after I had already written in my notebook, "No Pomatiopsis found", I found a live pair.
The larger snail was probably ~5 mm long.
Once I figured out where to look for them, it wasn't too difficult to find another pair; they must like to hang out in pairs.
So, almost 60 years and many floods later, Pomatiopsis lapidaria is still at Fletcher's Cove. I am planning trips to DeWitt's other 2 locations to look for the snails.
William B. DeWitt. 1952. Pomatiopsis lapidaria, its occurrence in the Washington, D. C. area and its laboratory rearing in comparison to that of Oncomelania spp. Journal of Parasitology, 38: 321-326.
On the 1st page of his classic textbook General Chemistry, Linus Pauling describes chemistry as "the science of substances—their structure*, their properties, and the reactions that change them into other substances". Then he compares the scope of chemistry with those of some other sciences, physics, astrophysics, biology and geology, and finally concedes that "[i]t is hard to draw a line between chemistry and other sciences".
It may actually be easier to decide if a given activity is not chemistry than it is to decide if it is chemistry. For example, if one is studying the influence of friction on the movement of a weight down a slope, that is not chemistry but physics; if one is studying the orbit of a comet around the sun, that is not chemistry but astronomy (and physics too); if one is studying the influence of a predator on a snail population, that is not chemistry but biology.
But if one is studying the influence of friction on the adhesive properties of a snail's slime by analyzing its chemical composition as a function of soil characteristics, is that chemistry, physics, biology or geology?
The oldest chemistry book I have is the English translation of Lothar Meyer's** Outlines of Theoretical Chemistry from 1892. According to Meyer, "Chemistry deals with the changes which affect the material nature of the substance. Chemistry, then, is the science which treats of matter and its changes."
Meyer's definition is essentially the same as that of Pauling.
One reason why we cannot pigeonhole every scientific activity into a category is that the fields of science do not and can not have clear-cut boundaries. The fields of science are not independent of each other. Instead, each and every field of science relies on others, derives support from them and, in return, supports them. I touched upon this notion briefly in this post.
*Shouldn't that be structures? **According to the title page, Meyer was a professor of chemistry at the University of Tübingen.
We saw this sign on a tree above the Monocacy River near Frederick, Maryland last Saturday. It is probably referring to the rusty crayfish (Orconectes rusticus), a non-native, invasive crayfish species.
We did it before. Now we have a chance to do it again for 3 months! The Royal Society has announced that on the occasion of its 350th anniversary:
The Royal Society Digital Journal Archive, which dates back to 1665, will be FREE to access from 30 November 2009 until 28 February 2010. The Archive contains every article ever published in the Royal Society's journals.
My favorite of them all is Philosophical Transactions, especially for the period from 1665 to about 1780. Those were the formative years of modern science. That was a time when most scientific knowledge was extremely limited and shallow; most scientific experiments and observations were crude and simplistic; most hypotheses the scientists were attempting to test were ridiculous by our standards.
That was when if you had a thermometer—not everyone did—you could measure the temperature in and outside your house and then get the results published in the world's premier scientific journal.
From Philosophical Transactions January 1, 1746, 44:613-616.
But, hey, science had to go thru that infancy period. It was a prerequisite to the present. If they hadn't reported the temperature difference between indoors and outdoors, we would be doing that now.
Enough said. I am taking my sack and flash drive and heading over to the Royal Society.
I have been keeping a land planarian, Bipalium adventitium, since about the end of September. In part 3 and part 4 of this series, I chronicled my attempts to feed slugs to it. In fact, I now have enough data for a short paper that I am co-authoring with Megan P.
According to several published studies (citations below), the preferred, and perhaps the sole, prey of this planarian are earthworms. Bipalium adventitium is a passive-aggressive predator. It doesn't seem to chase after its prey, but attack one only if it happens to bump into one while foraging.
Several studies have also described the predatory behavior of B. adventitium (citations below). When a hungry planarian makes contact with an earthworm, it climbs on the worm and everts its pharynx. The earthworm is quickly immobilized apparently by the planarian’s pharynx. The planarian then starts to consume the worm. Here is a photo showing the planarian eating a worm. Note that the planarian's mouth is not in or anywhere near its head; it's on the ventral side near the middle of the body.
The light colored tissue covering a portion of the earthworm’s body is the planarian’s everted pharynx (arrow).
During this process the worm continues to move its head or tail for up to 45 minutes, but is otherwise incapable of freeing itself from the planarian.
And here is a short film* of an earthworm being devoured alive by B. adventitium. The planarian, light brown, is on top of the darker colored worm. You can see one end of the worm moving. During the 2nd half of the clip, the planarian's head is also visible.
I don't know if earthworms can feel pain; if they do, this must be a horrendous way to die. But, as Richard Dawkins said in his book River out of Eden, "nature is not cruel, only pitilessly indifferent" to such petty affairs. Planarians must eat too.
To be continued.
*Once again, I apologize for the poor quality of the movie. This is the best I can do with my present camera.
Dindal, D.L. 1970. Feeding behavior of a terrestrial turbellarian, Bipalium adventitium. American Midland Naturalist 83:635-637.
Ducey, P.K. & Noce, S. 1998. Successful invasion of New York state by the terrestrial planarian, Bipalium adventitium. Northeastern Naturalist 5:199-206.
Ducey, P.K., Messere, M., Lapoint, K. & Noce, S. 1999. Lumbricid prey and potential herpetofaunal predators of the invading terrestrial flatworm Bipalium adventitium (Turbellaria: Tricladida: Terricola). American Midland Naturalist 141: 305-314.
Ducey, P.K., McCormick, M. & Davidson, E. 2007. Natural history observations on Bipalium cf. vagum Jones and Sterrer (Platyhelminthes: Tricladida), a terrestrial broadhead planarian new to North America. Southeastern Naturalist 6: 449–460.
Fiore, C., Tull, J.L., Zehner, S. & Ducey, P.K. 2004. Tracking and predation on earthworms by the invasive terrestrial planarian Bipalium adventitium (Tricladida, Platyhelminthes). Behavioural Processes 67: 327-334.
Zaborski, E.R. 2002. Observations on feeding behavior by the terrestrial flatworm Bipalium adventitium (Platyhelminthes: Tricladida: Terricola) from Illinois. American Midland Naturalist 148: 401-408.
