Naturespeak A naturalist's view of the world

February 1, 2008

Mayflies in February

Filed under: Uncategorized — wykes @ 9:02 am

  Out on the big waters of the Detroit River and Lake Erie life goes on beneath the cover of winter ice. Ice fishermen are well aware of this fact, although their version of the story is very icthyocentric (fish oriented).  To them the meaning of life comes in the form of a 14 inch Perch or a slab-sided Bluegill. Heaven’s gate is a round hole through the ice providing access to an endless procession of filets.  But when the point is forced, experienced fishers will grudgingly admit that there is more than just finned life beneath their feet.

  Truth is, just about every aquatic life form from mudpuppies to crayfish are active during the winter.  I saw a very large bullfrog tadpole cavorting around an open water patch two weeks ago and have heard reliable stories of painted turtles swimming under the ice. Yesterday a friend relayed a story to me that a fellow ice fisherman detected something “that looked just like a stick bug” crawling up out of his hole and out onto the ice. The unexpected guest turned out to be a Water Scorpion – not a scorpion at all but merely a spindly relative of the giant water bug. 

  One winter water critter that all fishermen are familiar with is the ever popular “wiggler.” These creatures are sold as bait, along with leaf worms, wax worms, mousies and the like. Unlike their shelf mates, wigglers are a natural part of the local offshore waters. Wigglers are actually insect nymphs officially known to the non-bait world as Hexagenia or Burrowing Mayflies (see here).

  It’s nice having such easy access to these entomological specimens because it saves you from taking a very cold dive to the lake bottom.  For a buck seventy-five, you can walk into a local bait shop and come out totally dry and in possession of a plastic bait container crammed with 24 mayflies. I discovered that I had 25 in my recently purchased container, but decided not to return the extra one (although I felt guilty for several prolonged minutes).  I released my charges into a larger pan of water for closer examination and would like to share a few observations with you.

  Swimming Mayfly nymphs manage to propel themselves in a manner similar to miniature whales – very clumsy tiny whales.  They rhythmically wave their abdomen up and down in order to move in a haphazardly forward direction. In other words, they wiggle (which is why fishermen call them wigglers rather than tiny clumsy whales). Burrowing mayflies are not built for sustained swimming, but they can be forgiven this aquatic inadequacy because they are built for, you guessed it, burrowing in the bottom muck. This is why they call them…never mind, you already know what I am going to say.

  Take a look at this shot and you can see that an individual nymph is about 2 inches long. I’ve provided a dime for size comparison (Mr. Roosevelt is just under ¾ inches in diameter here).  Those feathery things lining the side of the abdomen are gills.  Three tail filaments trail off the back end and six robust legs can be seen at the front end. A pair of beady black eyes, a like number of antennae, and a set of substantial tusks are evident on the head. All the parts are tinged with a pleasant golden hue that almost makes them look appetizing – at least to a hungry fish.

  It is the full intention of every young burrowing mayfly to become a big mayfly so they need to deliberately avoid predators while fulfilling their personal destiny to get fat. They start off as eggs laid the previous summer by the flying adults. Over the course of the next year, the nymphs (a.k.a. naiads) eat algae and detritus, and shed their skins many times to accommodate their growing size.

  Nymphs operate out of a small semi-circular tunnel in the bottom muck which they excavate with a powerful set of shovel-shaped front legs and stout tusks (features best appreciated from this angle). The passage has two open ends and the animal positions itself midway along its length. Constant gill motion keeps a steady flow of water going through the corridor and tiny particles of food are snagged in the hairy fringe bordering the head and legs. Every now and then, the nymph brings the fringe up to its mouth to take in the particulate goodness.

  It is mesmerizing to watch the waving motion of the gills as they pulse in sequential waves from front to back. The gills are operated in pairs. Their tips are brought together over the abdomen and smoothly returned to their side position.  A glance at these two images – first this one then this one – will give you an idea of what I’m talking about.

  My 25th mayfly didn’t last very long.  It died soon after I poured it and its container mates out into the water tray. My consumer guilt now completely gone, I thought about returning it to the bait store for a refund, but opted not to. Instead, I quickly returned the others to their container and placed them back in the fridge. It is crucial to maintain the chilled conditions of winter water because cold water retains more oxygen which is easier to retrieve by gilled critters.

  There are many features of Burrowing mayfly life that are noteworthy but only so much patience on your part to hear them. So, let’s boil this down to a few summary remarks. Ecologically, it’s important to note that Hexagenia are one of the most important sources of fish food in the entire lake system. They are eaten as nymphs and adults. When they emerge as winged flyers in June or July (not May) they will temporarily take over the near shore world and everyone will know them as those “blanky blank fish flies.”  Mayflies live for that brief 48 hour period when they can break the bonds of the water world.  Until that time they bide their time in relative obscurity beneath the winter ice – known only to fishermen and the fish they seek.

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