They are a water beetle and should be in the pond. Don't know the proper name.

By the looks of the large size of it on that plate in the first picture it appears to be what is commonly known as the Great Diving Beetle. You can see that the front legs have suction cups which helps hold onto their prey and the back legs have hairs which form swimming paddles. They live in ponds eating fish, polliwogs, etc. To find a new pond they fly on moonlit nights and when they see the moons reflection below they know it's a body of water that they can land upon. Of course this method of location developed before humans built roads, parking lots and patios so when it sees the moons reflection upon these surfaces when they are wet it will suppose that they are bodies of water too and it will land. Street lights also louse things up for this beetle too as far as finding a new foraging areas is concerned. By the way handle with care, it can give a good nip.

Loosetrife it must be at least 60 years since I saw the word pollywog - thank you for the nostalgia trip!

what is a pollywog? never heard of it before.

Yes, It's a wonderfull word which has two absolutely acceptable different spellings.....polliwog or pollywog. When I was a young sprout and I asked my father " WATS DAT?" he told me that it was a polly(i)wog.

A polly(i)wog is also known to some as a tadpole. Steragram, at my age my short term memory banks are blowing away and the long term memory ones are filling in the void...I'm starting to skip back down the road to my youth:)