At the bottom left of the drop is one of those amazing animals: Springtails
If you look well, there is another one sitting on top of the drop.
More information on Springtails:
Pond life
Collembola.org
Because Springtails are in the following family:
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Entognatha
Order: Collembola
