25 May 2008

Gastropods of Hoyles Mill

Taking advantage of yesterday's nice weather, Megan and I explored Hoyles Mill Conservation Park in Montgomery County, Maryland.

Hoyles Mill is a secondary growth forest roughly 1 mile by 1 mile in dimensions. It is currently undeveloped, meaning that there are no roads, restrooms, offices, playgrounds, etc., within the park; there is only an unpaved road closed to traffic that goes alongside the park. The area will hopefully stay that way.

We found the usual mixture of introduced slugs and native species in apparent peaceful coexistence. Here is an Arion subfuscus, an alien originally from Europe, eating a mushrooom. The large circular hole is the slug's pneumostome, the breathing hole that leads into its lung.


Frequent outcrops of large rocks broke the monotony of live trees and dead trees and leaf litter. At one spot, the creek flows over a massive single-piece rock that forms its bed.


Here is an assortment of the native gastropod species we saw. At the top is a Megapallifera species; bottom left is an empty Mesodon thyroidus shell next to a live juvenile; bottom right is a Ventridens ligera. We also found Philomycus carolinianus, another native slug and the snail Zonitoides arboreus.


For me, the best discovery of the day was these live Anguispira fergusoni that Megan found on the underside of a rotting piece of wood.


This record extends the range of this species known to me about 2 miles south. Down along the Potomac River, about 6.5 miles south of here, Anguispira alternata is common. A long time ago, somewhere between here and the Potomac the ranges of these 2 Anguispira species must have approached each other and perhaps even overlapped. The intervening areas have since been heavily developed but fragments of some 2nd growth forests remain. It would be a stimulating endeavor to try to locate a place where the 2 species may continue to coexist.

1 comment:

Anonymous said...

Wow look a face at bottom of rock!!