I wrote about the land planarian Bipalium adventitium in this
post. That individual ended up in a vial of alcohol soon after
that post was written. Last Friday, I found another one under a
log in a park. There were also earthworms in the soil under the
same log; they are the planarian's main, if not the sole, prey.
Here is a picture I took in the field; the planarian was still
on the underside of the log. It's hard to give dimensions for
these animals, because their bodies are very stretchable. In
this picture, the planarian was probably ~4 cm long. I have also
taken several video clips of it while it was crawling on a glass
plate. Here is one of them. Excuse the quality; this is the best
I can do with my current camera. Notice how it moves its head
from side to side as it crawls. That's the characteristic
behavior of these planarians. The lateral movements of the head
presumably enable the sensors on the head to pick up chemical
clues from the environment. The planarian hasn't eaten for at
least about 50 hou