Predaceous Diving Beetles Remaining Active
While meadows and fields are experiencing a sharp decline in insect life at this time of year, one habitat where insects remain active in the fall and often through the winter is ponds. Among the year-round active pond invertebrates are Predaceous Diving Beetles, which can still be observed as they row through the water, intermittently surfacing to thrust their abdomen above the water line in order to procure a bubble of air from which they breathe. Their middle and hind legs are fringed with long hairs, making them efficient at rowing through the water in search of prey or detritus to eat.
Predaceous Diving Beetles lay their eggs on and in plants above the waterline in early spring. When the eggs hatch, the larvae drop into the water. Mature larvae crawl out of the water to pupate in damp chambers on the shoreline. They emerge as adults and re-enter the water, where they remain active through the winter, under the ice. (Water Scavenger Beetles look a lot like Predaceous Diving Beetles, but they stroke first with one leg, then another, not simultaneously like Predaceous Diving Beetles, and they come to the surface of water head first to secure air.)
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Naturally Curious with Mary Holland 
Mary, I’m so glad I got to meet you at the Northern Woodlands Writers Conference… and to find out about your exceptional blog. A fascinating and wonderful bit to start the day, just like you! Many thanks and best regards, Nancy Baker
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October 31, 2014 at 11:56 am
Thanks so much, Nancy!
October 31, 2014 at 2:03 pm
What a great photo! I’ve watched these guys in action, but it’s nice to see one in such detail. One spring I made the mistake of including a predaceous diving beetle in the pond-water aquarium that I set up in my classroom, and we proceeded to watch it attack and feast on one after another of the various other pond critters that were swimming around, till I scooped it out and returned it to my pond. It was really interesting at first, but became slightly horrifying, as I realized that the other critters had no way to escape or effectively hide!
Thanks! – Dell Waterhouse
October 31, 2014 at 2:27 pm
I getting a giggle out of how this beetle looks like it is magically flying through the air with only those little “wings”.
October 31, 2014 at 2:47 pm
How big are they? When I was scooping a bucket of water out of the lake a couple of weeks ago, there was something about the size of an apple seed swimming merrily around the bucket – think it was tinier than this guy, but it sure was fast! And the water was about 50-degrees, so I was surprised to find something that active.
October 31, 2014 at 3:44 pm
They’re bigger than what you saw…about 1/2″. Bet you had a whirligig beetle!
October 31, 2014 at 5:10 pm
Are these what we call Water Boatmen? Great macro shot, complete with leg fringe!
November 1, 2014 at 8:35 pm
Hi Eliza! Water Boatmen are a different species of beetle, but they row the same way!
November 1, 2014 at 9:44 pm