15 October 2008

Steel and slime


This steel bridge, about 15 m long, spans across Little Seneca Creek not too far from my house. One rainy afternoon in late September I was walking across it when I spotted a slug crawling on the railing at about the middle of the bridge. It was one of the native slugs that are common around here, a Megapallifera, possibly M. mutabilis.


I couldn't quite figure out how the slug might have gotten to where it was. There are woods at each end of the bridge. So it is possible that the slug simply got on the bridge at one end and kept crawling until it got to the middle. A less likely possibility is that it fell from the overhanging canopy (they do climb trees), which is about 10 m high. Although, I am not sure if it would have survived a fall from that high onto steel.

After taking its pictures, I moved to slug to a beech tree in the nearby woods.

1 comment:

Anonymous said...

If they climb trees, they are likely to climb bridges too. It's hard to tell if there is any lichen on the bridge, and harder to tell if the slug thinks there might be lichen on the bridge.

Remember that the smaller you are the less dangerous falls are. A ten meter fall gives a velocity near 15m/sec, but terminal velocity for something that size is of the same order of magnitude, so air resistance will reduce that. Call it 10m/sec.

I'm quite a bit more unsure of what a survivable impact velocity is for a slug. A human scaled to that size would barely feel anything, but a slug has no bones. It is soft, but can probably survive a fairly large deformation. With essentially no numbers to back it up, my guess would be that all but the largest slugs can survive a fall from any height (in air).

I hope you are enjoying your trip.