Subject: Star Trek brain eater
Location: Mississippi River, central Louisiana
March 28, 2015 5:14 pm
Don’t go near the water! Found this thing in the Bayou of central Louisiana at the end of March. My research has turned up some similar creepy crawlies but nothing quite the same. What is it?
Signature: Boatswain

Water Tiger and Mosquito Tumbler

Giant Water Scavenger Beetle Larva and Mosquito Tumbler

Dear Boatswain,
We absolutely love your colorful description of what we originally thought was a Water Tiger, the aquatic larva of a Predaceous Diving Beetle in the family Dytiscidae, but once we searched BugGuide and compared your individual to images of larvae of Giant Water Scavenger Beetles in the family Hydrophilidae, we determined that was the correct identification for your creature.  According to BugGuide contributor Andrew Tluczek:  “I have a masters in Entomology and have worked with aquatic insects. It is a Hydrophilidae. The mandibles have ‘teeth’ which Dytiscidae larvae do not have.”  Your individual has “teeth” on the mandibles, and other research turned up additional physical similarities.
  According to the University of Wisconsin at Milwaukee Field Station site:  “WSB [Water Scavenger Beetles] larvae are described as ‘sluggish’ and are found crawling on the pond floor or climbing on underwater vegetation. The larvae is a ‘couch-potato’ version of the sleek PDB [Predaceous Diving Beetle] larvae/ water tigers (pictured) (they sometimes share the ‘water tiger’ moniker). WSB larvae often have paired, gill-like structures protruding from the sides of their abdomens. Their feeding category is ‘engulfer-predator;’ they use their hollow jaws to suck out the juices of their prey. Their food-list includes their brethren; they love mosquito larvae but will go after mini-fish and so are an unwelcome addition to a koi pond. Larvae back their abdomen up to the water’s surface and take in air through spiracles (pores) at its tip. They spend a month underwater as larvae and about 12 days pupating in a cell in moist soil.”  That information thrilled us as we can now safely use the term Water Tiger to describe the larvae of aquatic beetles in both families.  According to Bugwood:  “Larvae, which occur in water, have an elongate body and large dark head with prominent curved jaws. Elongated spiracles through which they acquire oxygen arise from the end of the abdomen. … The immature stage is a predator, working by ambush to lie in wait, seizing and crushing prey that comes within reach. Most of their diet is made up of small insects and other aquatic invertebrates. However, their jaws are quite powerful allowing them to consume snails whole as well as catch large prey such as tadpoles and small fish.”  A Mosquito Tumbler, the pupa of a Mosquito, is visible in two of your images.  We have selected your submission as our Bug of the Month for April 2015.

Water Tiger and Mosquito Tumbler (front and center)

Water Tiger and Mosquito Tumbler (front and center)

Water Tiger

Giant Water Scavenger Beetle Larva

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Location: Mississippi River, Louisiana

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