The scales on moth wings help camouflage them from predatory bats because their uneven shape prevents the bats' sonar from detecting them clearly.
"The moth's first defense again comes from those fuzzy scales it has all over its body. To us they just seem ungainly, a mistake. But because of their uneven shape, they give the bat only a fuzzy outline on its sonar scope." (Bodanis 1992:169)
Learn more about this functional adaptation.