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.)

vrtgwntr

1 comment:

pascal said...

I envy the fact you have snails in your own yard. Our is just turf grass right now, but we're trying to build in brush/deadwood. Mostly for songbirds, but we'll see what snails show up.