Tuesday, August 13, 2013

Water Tigers

Water tigers live in ephemeral pools, devouring tadpoles, fairy shrimp, mosquito larvae and anything else it can grab with its jaws. These 2-3 inch long larvae of predaceous diving beetles are some of the most vicious predators in the desert suburbs, sucking the guts out of their prey and then disposing of the empty carcass. There are about a dozen species of predaceous diving beetles in North America, named Dytiscus in Latin, which means "great diver." 
My first encounter with a water tiger was here at a pond in Skunk Creek, just east of I-17 near the pedestrian bridge north of Jomax. Monsoon storms in late July this year revived myriads of critters that wait patiently in a dormant phase for water to return to the desert. When I first saw the dim outline of the larvae swimming in the murky water, I thought it was a small fish...but there are no fish in this usually dry wash. We captured one with a net and found that it had six jointed legs near its fearsome jaws, tipping us off to its identity as an insect. 

At rest, the water tiger will lift its rear end to the water surface to breathe through a pore or spiracle at the tip of its abdomen. Like their adult form, a large flat beetle, they are elegant and rapid swimmers. The larvae will pupate in the mud once the pond begins to dry, emerging as an adult when the next storm cycle revives the ponds it lives in. We never saw any adult diving beetles, but did witness plenty of water tigers prowling in the pools. 

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