EPOW - Ecology Picture of the Week

Water Scavenger Beetle in the Light

Water Scavenger Beetle (species unidentified), Family Hydrophilidae
Thekkady, Kerala, India

Explanation:  It is past dusk.  I am sitting on the porch of my bamboo hut, here in south India, on the outskirts of Periyar Tiger Reserve.  It is "just sultry" as they say, humid and hot with no wind.  

I turn on the porch light and presently am greeted with a fine array of nocturnal invertebrate visitors ... including this hefty specimen that lands at my feet.  

This is a water scavenger beetle.  These arthropods are amphibious -- well-adapted to living in water but also capable of strong flight and a terrestrial capacity.  
  

Note the feathery appearance of the tarsi (legs), which
aids in swimming, giving away this beetle's aquatic lifestyle.
 

The adults, such as this specimen, are largely herbivorous but some also consume carrion, and some prey on other insects.  The larvae are something else; they are all carnivores and even cannibals.  

And yes, they "bite."  Actually, their sternum, on the underside, is elongated into a sharp spine which is used to jab potential predators, including the careless handler (no, I didn't get jabbed, as I know better, luckily!).  

They seem to be attracted to lights at night -- thus, this specimen's appearance here -- which they might confuse with light reflecting from the surface of water.  
  

     
Water scavenger beetles are similar to predaceous diving beetles (of family Dytiscidae), but the two kinds of beetles can be told apart by their antennae.

Look closely here.  The antennae of this specimen are short, and clubbed, and shorter than the maxillary palps (one of which is visible in this photo just beneath the insect's left antenna), making this a water scavenger beetle.  Antennae of predaceous diving beetles, on the other hand, are threadlike and longer.