The flightless marine insect Halobates robustus Barber (Hemiptera: Gerridae) occurs on the surface of the coastal waters of the Galapagos archipelago, frequently aggregated close to mangrove and lava edges. Its food consists almost exclusively of dead insect prey floating on the sea. Feeding is carried out by solitary individuals which leave the non-feeding flotillas and adopt a characteristic hunting behaviour. Hunting occurs largely at high water, which, together with a tendency to remain close to mangrove edges during tidal flow away from the shore, reduces the possibility of the insects being swept into the open sea. Predation by fish, birds and a reptile is reduced by extremely effective avoidance behaviour by the flotillas.