Predaceous Predator of the Pond

Larva of the Predaceous Diving Beetle - REK

Linda Bower sent this story and video of a Predaceous Diving Beetle larva living up to its name.  It brought back painful memories of my first encounter when I grabbed something slithering around in a net full of pond sludge and came up with the final instar larva above, clinging to my finger while trying to digest it through its fangs.  In less that a minute my finger was swollen up to my palm with the pain of a wasp sting and it took an hour for the swelling to go down.

Predaceous Diving Beetle - REK

Linda's story
The larval Predaceous Diving Beetles are such voracious predators, they have earned the nickname "Water Tigers." In addition to feeding on its own kind, the attacker in this video ate a Waterflea, two Ostracods, a Copepod, and unsuccessfully attempted to catch a tadpole several times, all in under 2 hours.

The Dytiscid family is estimated to include about 4,000 species in over 160 genera. According to Beetles of Eastern North America by Arthur Evans (2014):

"Much remains to be learned about larval Dytiscids (several genera remain undescribed as larvae). Adult Dytiscids are among the most commonly encountered aquatic beetles. They can be found in almost any aquatic habitat, from rain puddles and birdbaths, springs, seeps, swamps, ditches, ponds and lakes to streams and rivers. They are notably absent from deep water." 

The larvae in this video are probably in their 1st instar because they are so tiny. The larger ones can inflict a painful bite. It was filmed in a farm pond with a digital microscope on May 12, 2017 in the Missouri Ozarks, USA. 

2021 Update  Smithsonian has a good video feature on Giant Diving Beetles.