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Photo#214608
Hydrophilus larva (Hydrophilidae) - Hydrophilus

Hydrophilus larva (Hydrophilidae) - Hydrophilus
Naples, Collier County, Florida, USA
July 31, 2008
Size: 75 to 80 mm
I was going to post this in dragonflies but thought starting it here might make the placement a bit more specific. This larvae was in a flooded drain ditch feeding on tadpoles and mosquito larvae.

Moved
Moved from Cybister.

Sorry..wrong family!
After revisiting this image, I noticed that the antenna insertions are in the wrong place for a dytiscid (usually on the outer margins of the head). The asymmetrical mandibles and large size indicate that this is a Hydrophilus larva (Hydrophilidae).

Moved
Moved from Predacious Diving Beetles. Thanks for the detailed explanation, Tim.

Cybister sp.
Not something I've personally encountered but the large size and lack of cerci (tails) points to this genus, based on the provided manual to Florida water beetles (Epler). The presence of a "tooth" at the anterior region of the head (barely visible here in this image between the maxillae) is also diagnostic. Dytiscus larvae (which i've seen and collected), which are slightly smaller (to 6 cm) have prominent cerci and dense lateral fringes of hair on the last 2 abdominal segments and cerci. The anterior portion of the head is rounded unlike Cybister. Also according to the manual Dytiscus sp. are virtually absent in Florida.

you might try...
searching images of various aquatic beetle larvae (e.g. Dystiscidae).

 
Thank you.
Thank you for the lead on the ID. I totally missed it guessing it was a dragonfly larvae.

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