About a month ago we filled a small tray with water and left it in the undergrowth at the bottom of the garden. A few days ago I noticed there were now quite a few small creatures swimming about in it.
Captured here is a Hoverfly Larvae or Rat-tailed Maggot. Their long telescopic tails link up to the surface of the water and acts as a snorkel. Look carefully and you should see another few tails connected to the surface of the water.
I found this quite hard to photograph. I battled against poor light, reflection from the surface of the water and focusing on the subject below. They are also wriggly little things.