West Bath, MaineIf you close your eyes, a green crab scuttling up your forearm feels more spider than sea creature, its little legs picking their way as if spinning silk. If you open your eyes, you will see the forged work of 200 million years: bumpy carapace, plated apron, calcified pincers. The small crabs are exquisite, seemingly carved from jade. The big ones are monstrous looking. They are nimble and chaotic, and likely under any beach rock in the Gulf of Maine.

But here, the European green crab is not native. It is an invader, a species that traveled to the region in the 1800s in the ballast water of trading ships. In the centuries since, the crabs have established a