Predaceous Diving Beetles

Animals, July, 2000 by Sy Montgomery

A better way to move these animals around is with a net. If you take some home in a bucket, you can watch them in an aquarium. But make sure the aquarium has a lid, advises Chandler. Otherwise the beetles will fly out. Many of the pings that hit your windshield in April are predaceous diving beetles that have just emerged from ponds where they groggily spent the winter. When they wake, they mate and then fly, looking for the glistening surface of a warm, sun-reflecting pool--which to a beetle looks just like the surface of a shiny car.

The larvae, which are wingless, make better aquarium pets. You can find both adults and larvae in spring. One caveat: don't put another creature in the tank. Chicago nature photographer Jim Rowan learned this after collecting a water tiger along with other aquatic organisms, including some baby salamanders he planned to photograph. "I was doing fine, photographing the salamanders," he said, "until all of a sudden the water tiger starts eating them."

Normally, when the water tiger waits for its prey, it rears up like a cobra with mandibles open wide. But occasionally the predator gets impatient. Yves Alaire, a specialist in water tigers at Laurentian University in Ontario, saw a water tiger stalking a caddis fly larva. These larvae live at the bottoms of streams inside little cases they build from pebbles, sticks, or leaves, which they cement with their saliva. The water tiger usually sits on the case and waits until the caddis fly pokes its head out, then bites the head and shakes it free. But one time, he said, the caddis fly wisely refused to emerge--so the water tiger bit right through the caddis fly's case and killed it in its own home.

What force could stop such a fearsome predator? Another predaceous diving beetle. They're so predaceous that both larvae and adults will ear each other. Only one other creature can match their appetites, and that's a human. Predaceous diving beetles can't eat us--but we can eat them. In China, and in Chinatowns around the world, folks collect these beetles beneath streetlights, pull off the legs, wing covers, and head, fry them in oil, season them with salt, and eat them like nuts.

Sy Montgomery is a contributing editor for Animals. Her latest book is Journey of the Pink Dolphins (Simon & Schuster).