Monsters of the Not-So-Deep

The myth of the large larvae is vindicated: we've found a second one! 
       About two weeks ago, we were wading across a very shallow, algae-covered South Platte River.  The air temperature was wavering around the high 90's, and even a few inches of cool flowing water provided refreshing relief from the heat!  The kids in the program were unsurprisingly hesitant to leave the river, and one boy was dragging his net as well as feet.  When we were at the point bar half way across the river, he suddenly gave a shout.
      "Hey, Miss E!  I caught you something!  What is it?"  The weird thing he held in his hand was a new find amongst a year's worth of poking under rocks for aquatic invertebrates*.  The creature was about two and a half inches long and the thickness of a very squashy pencil--HUGE for an aquatic larvae in this river.  For reference, most larvae we find in the river around 1/4 of an inch long. This one looked like nothing so much as a smooth, very large brown caterpillar with tiny tentacles coming out of one end, which end we weren't sure.
         Back in the office we excitedly made use of the internet to confirm the identity of the stranger.  Based on verbal descriptions (the river beast was left to cozy back up to his (her, its?) rock), we determined that the larvae was most likely that of a crane fly. 
      Like many of the tiny inhabitants we find on the underside of river rocks, the crane fly larvae go through amazing changes before they become adults, and by the time they are fully grown up, they have wings and are living entirely on land and in the air!  As adults, crane flies look like a large, elegant version of a mosquito.  The good news, though, is these bugs won't bite.  Crane flies feed on plants, plant debris, or other insects, depending upon the species.

Photo from the EPA public domain http://www.epa.gov/bioiweb1/html/craneflies.html

     The Jr. Rangers (10-12 year olds) turned up another crane fly larvae in the river today.  We're glad to find them here, and not just because they make for a curious creature to inspect.  Aquatic invertebrates serve an important role in our park.  They are the bottom of our food chain and provide a meal for larger animals such as fish.  In turn, those fish become food for even larger animals such as herons and other birds.  
     The teeny-tiny animals in our river also help us to know how healthy our river is.  Some aquatic invertebrates do not survive well if the water is polluted, too warm, or low in oxygen.  Crane fly larvae can only survive in water that is moderately clean^.  You'll have to look closely to find them though.  Crane flies and other larvae blend in well with the rocks that are their homes, but when you take the time to inspect with care, you never know what or who you might find!



*aquatic invertebrates: underwater insects and other underwater animals that do not have a backbone.  This group includes larvae, water spiders, crawdads, and many others!

^This is according to the EPA webiste, which states that crane fly do not survive well in polluted waters.

Discussion Questions:
1. What is the most surprising animal you have ever come across in the wild?  Where did you see it?

2. What are some factors that can make a river polluted?  Are there little ways you can help to keep a river clean?