Bruce, you might be able to use a BT product to get rid of that caterpiller in your pond. Bacillus thuringiencus isrealei (BTI) is meant to kill mosquito larvae in water, but it might also parasitize the lily caterpiller if it gets down to the water level. This form comes in donut shaped things called mosquito dunks (look at Home Depot). The other form that should work is "regular" BT, one brand you'll find is Thuricide. It's a liquid concentrate, put in a hose end sprayer. (Keep the bottle in the fridge so it'll last longer.) It stops the caterpillers (or web worms, etc.) by not letting them digest what they eat, so they stop eating and die. Don't broadcast this farther than you need it because it will kill butterflies (since they are from caterpillers, it kills the mature form of the critter also).

Every so often I'll see interesting bugs that I've photographed, though I don't always follow-up to learn more about them. Here was some kind of slow-moving dung beetle (yes, that is dog poop in the background) that was two or three inches long. Very striking eye spots.

SRS