Herring Gulls prey on marine invertebrates, fish, insects, smaller seabirds, and even on adults, young, and eggs of other gulls. Along rocky shores, they take mussels, crabs, sea urchins, and crayfish. On mudflats, they seek worms, small clams, and mussels. In open water, they follow large predators (including fishing boats) that bring small fish, squid, and zooplankton to the surface. Newly plowed fields provide ready supplies of earthworms and other invertebrate prey. Herring Gulls are opportunistic scavengers on fish, carrion, and trash. Individual gulls often specialize on a food type. Most choose marine invertebrates like crabs, sea urchins, or clams, even though fresh-caught fish make their most calorie-, protein-, and fat-rich meals by far. In spite of this apparently poor choice, these gulls have the largest, heaviest eggs and the highest hatching success rates. The opportunism of gulls extends to raiding nests of other seabirds, and one or two males per large breeding colony may even specialize in cannibalizing chicks of others in the colony.