Giant water bugs (Lethocerus americanus) are large (over two inches long) insects that spend most of their lives in bodies of water such as ponds and lakes. They are predators, capturing prey with raptorial forelimbs, and then killing prey with an injection of venom that aids digestion. Giant water bugs are capable of capturing and consuming small vertebrates such as fish and frogs. The photograph above shows a giant water bug eating an adult male pacific chorus frog (Pseudacris regilla)at a pond in Napa Co., CA.
Over the course of five years of studying the life history of pacific chorus frogs, I collected data on which frogs were captured by giant water bugs. It turns out that giant water bugs capture large male pacific treefrogs much more often than would be expected by chance (Benard 2007). Several possible explanations exist for this observation. Giant water bugs may actively seek out and consume large frogs rather than small frogs. Alternatively, large frogs may be more active than small frogs, and as a consequence, be more likely to encounter giant water bugs.
These frog-eating insects are in the insect family Belostomatidae. There are three genera of Belostomatidae in North America. The giant water bugs, Lethocerus, are the largest. The other two genera, Belostoma and Abedus are also predatory, but smaller in size. In all three genera, males care for eggs until hatching.
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