Pearchplucker,

Whirligig beetles do get eaten by fish and other critters on occasion. They can secrete a foul-tasting liquid if threatened and their grouping behavior helps to confuse predators. So often times fish do leave them alone because of the bad taste.

Check out this website http://www.pnas.org/content/97/21/11313.full.pdf. This is a experiment on Chemical Defense : Whirligig Beetle vs. Laremouth Bass