We put boards down between the veggie rows in our garden to reduce compaction of the soil which contains a lot of clay. As I move the boards, I almost always find beautiful black beetles hiding underneath them. About the size of half of my thumb, they are shiny black with iridescent blues, purple, or greens around the edges of the body and three rows of dimples on each wing cover (elytra). In some the wing covers may be bronzed. When I lift the boards, the beetles quickly scurry away in search of another hiding place. I always feel I should apologize for disturbing them.
I admit I was a bit concerned about having them in my garden when I discovered they are the introduced European Ground Beetle (Carabus nemoralis), also known as the wood ground-beetle or carabid. They have been found in every province in Canada with perhaps the exception of Manitoba. These, and other non-native soil dwellers, were brought here from Europe around 150 years ago in soil used as ship ballast.
If not in the garden, they will be in wooded areas under litter. They are especially noticeable now as they mate in April and May. They lay their eggs in the soil where the larvae hatch and feed before pupating.
Even though some people might consider them as pests, it appears that they are desirable in the garden as predators because they eat many kinds of invertebrates and garden pests. They will even chomp down on the eggs and young stages of the slimy European slug which also like to hide under the boards during the day.
Anything that eats introduced slugs is welcome in my garden.