Our resident videographer, Linda Bower, has been into leeches lately. The ones seen here are Placobdella picta, a species that specializes on juvenile amphibians. Her two months of filming has captured their movements and especially their interesting association with tadpoles. The ones seen here in this video are on spring peeper and gray tree frog tadpoles. A time lapse shows blood moving in the leech. Note the young leech attached to the glass from 1:54 to 2:25 minutes. The white dots swimming around are mostly ostracods.
Linda has been communicating with Malcolm McCallum who has researched P. picta and their association with tadpoles described in this paper. P. picta is known to parasitize 12 amphibian species including salamanders, frogs and the American toad. They find their future host by detecting vibrations from the swimming amphibians.
There is speculation that this species may be an important regulator of tadpole populations. Many frogs return to the waters where their own eggs were deposited. They are a known vector for several blood-parasites and may play an important role in amphibian declines.
This video has closeups of the leeches which have not attached to a tadpole. It includes views of "hanging out," "walking," reacting to copepods, and the inevitable guts moving and eliminating waste. At 3:22, the leech goes inside of an air bubble and then back into the water, which is very cool to watch.
Notice you only see hind legs on the tadpole. More on that soon.