Thursday, August 19, 2010

Other Creek Creatures

The creek, formerly a long single body, has now been fragmented into individual pools. This happens every year and it always makes me think of Darwin and his divergent finches. When water flow was high, the aquatic animals could move from pool to pool by swimming upstream or drifting downstream with the current. Now the organisms are trapped in their individual pools and their lives will interact only with others of like fate. Given many thousands of years, organisms from each pool could differentiate into a multitude of species. Of course, most of the pools will be dry in two months, so the possibility of new species is just an idle thought.

The larger pools contain abundant life. This small salamander larva still has plenty of area in which to hunt and hide. In order to survive, it must lose those gills and become an air breather before the pool disappears.

Crayfish stalk the pools looking for prey. As the pool shrinks, the prey becomes more concentrated and easier for the crayfish to capture. Shrinking pools also make it more difficult for the crayfish to escape from predators such as raccoons and herons that follow the creek and examine each pool for tasty morsels. When the water disappears, crayfish have the options of burrowing into the creek bed to await the rains or taking off overland in search of better living conditions.

When Water Striders find conditions not conducive to survival, they take shelter in protected areas near the creek. I found several wedged beneath flat stones in the creek bed, waiting for conditions to improve.

These pools are still receiving fresh water. There is a small flow moving down the creek channel, but it’s traveling through the gravel of the creek bed and is not noticeable except in the pools. Tiny pools such as this could persist for weeks if ground water levels stay high.

There are a lot of small insects trapped in the tiny pools. Dominant in this pool are young Water Striders, Riffle Bugs, Mayfly larvae and some type of fly larvae. If the pool had been large enough to support fish, most of these guys would have been gone.

If any of the insects do make it to flying adults, they’ll have to dodge this conveniently placed spider web. When emerging, many insects tend to come straight up from the water. Aquatic insect courtship activities often take place above the water in which the eggs are to be laid. For these reasons, some species of spiders habitually locate their webs above the water.


  1. Smart spiders! I have just learned a little about crayfish here in Maine and how some non-native species are invasive. Their numbers are growing and it is becoming a real problem! I had no idea. My sister is working with the data for her master's thesis. ~karen

  2. Very cool! Poking around in the stream looking for critters was one of the best parts of my job in Ohio (thought our stream was never reduced to individual, fish-less pools, at least while I was there). The insect larvae loving the lack of fish reminds me of talking about vernal ponds with students. "So, do you guys think there are fish in this pond?" "Sure!" "Well, remember there aren't any streams connected to the pond, so how would fish get here?" "Um... birds brought them!" Riiiiight.

  3. Karen - That sound's like some interesting research for a thesis. Certainly more exciting than the water management policy research I did in school.

    Hi, Rebecca - I hear the stories all the time. It's a wonder water birds can get off the ground with their feathers full of fish and fish eggs.

    I've been following your progress toward Georgia. You've certainly taken the scenic route to get there. It shouldn't be long now before you start the new job.

  4. Ha ha - I've been visiting family in Arizona in the interval between jobs (and it's from here that we took our rather ambitious road trip). Georgia next week.