I notice a lot of ladybugs around the redberries cactus, trapdoor spiders only come out of holes in the ground, slugs, centipedes, inch worms, glow worms, red worms, earwigs, and termites are mostly on the river bank but sometimes walking into the walls of buildings or houses or fences. Wasps are usually up in the Northeast corner (so are horseflies) but sometimes between the port and the cave (wasps are worth 220 coins!).
Tiger beetles, Rhino Beetles, and Longhorn Beetles are on trees, obviously, and they have a shadow at the bottom of the tree if you can't see them, you can see the shadow. Cicadas are at the bases of trees.
Mosquitoes and crane flies follow you around, pretty much. Red Lilly Beetles are usually near ladybugs and they're worth 140 or 160.
Spiders and crickets seem to like tall grass. Flies like weeds, and there are always flies buzzing at the northwest corner of the northern lake, a few steps north of it. (Unless there are weeds around to distract them, then they flit from spot to spot like butterflies).
There's occasionally a horsefly south of the southern lake.
That's all I can remember right now.