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Moving Water Habitats

Many odonates inhabit moving waters.  Moving water habitats include rivers, streams, and seeps.  Since some odes prefer rapid water,  and others slow moving waters, we have separated the two.

Rivers are larger than streams and can be defined as any body of water flowing in one direction, usually emptying into a lake or ocean. When a rushing river reaches a flat expanse, it undergoes a dramatic change.  The waters spread out and slow down, depositing their load of silt and creating a soft, muddy bottom.  In many cases the river becomes a series of meanders and oxbows.

In the sluggish part of a river, the water if warmer, richer in nutrients, and more conducive to plant growth than it is upstream.  Thus a large growth of water lilies and other vegetation may shelter an abundance of insect life, reptiles and amphibians.

There are rivers that are fast moving and those that are slow moving.  Some may be both at different stages.  For this website we felt it necessary to differentiate between the two.  Some species of odes prefer fast moving waters, while others prefer slow moving waters.  If that's weren't enough, some odes prefer sandy bottoms while others muddy or gravelly.

As in fast moving streams, organic materials do not accumulate so easily in fast moving rivers, therefore the food source on fast moving rivers is usually limited. Plant life is scarce and usually limited to the outer banks. Most aquatic organisms are swept downstream by strong currents and turbulence. The fast currents within the river produces riffles and rapid waters which are attractive to some very habitat specific odes such as Riverine Clubtail (Stylurus amincola), Cobra Clubtail (Gomphus vastus), Stygian Shadowdragon (Neurocordulia yamaskanensis).

Slow Moving River
When a rushing river reaches a flat expanse, it undergoes a change.  The waters spread out and slow down, depositing their load of silt and creating a soft muddy or sandy bottom.  In many cases the river becomes a series of meanders, oxbows and horseshoe shaped bends. In the sluggish part of the river the waters are much warmer and richer in nutrients, thus more conducive to plant growth than it is upstream.  When more plant life is present it produces a greater food source for many insects and amphibians.  A good variety of odonates are therefore found inhabiting slow moving rivers, some species of the Clubtail family prefer sandy bottoms such as the Elusive Clubtail (Stylurus notatus), Arrow Clubtail (Stylurus spiniceps), Skillet Clubtail (Gomphus ventricosus), Common Sanddragon (Progomphus obscurus),  while others such as Prince Baskettail (Epicordulia princeps), Illinois River Cruiser (Macromia illinoiensis), prefer muddy bottoms. And there are those who prefer gravel bottom rivers such as the Phygmy Snaketail (Ophiogomphus howei)

The biggest source of food in a stream is not the plants, but waste material from outside the stream, especially where a stream runs through a forest, dead leaves and rotting wood fall into the water and form a community of things, beginning with bacteria, fungi and other living organisms that breakdown the dead materials.  These organisms form the slime around rocks and leaves in streams, and are the main food source for aquatic larvae, allowing many insects to live beneath  stones and gravel.

In most swift streams, shallow riffles alternate with deeper pools; where the gradient drops sharply, waterfalls and white-water rapids appear.  Because of the current and turbulence in swift streams, organic materials do not accumulate easily.  Thus the primary food supplies occur in a different type of habitat within the stream, its riffle regions. Riffles (regions where there are shoals and shallow rocky areas for organisms to adhere to).  Riffles appear as ripples visible on the waters surface. Few aquatic plants other than algae and mosses appear on swift streams. Generally there is not an overabundance of odonates either, but the ones that are attracted to them are some of our less common ones, such as Snaketails.

Most fast streams mature and eventually turn into slow moving streams.  In a mature slow moving stream there is a progressive downstream movement of meanders, leaving shallow or deep pools, backwaters and oxbow ponds. Water in slow moving streams is generally warmer than that of faster streams, allowing a growth of microorganisms,  Since food supply is abundant, these streams are dominated by aquatic insects and invertebratres.  Many odonates in their larval forms find this the ideal home. Some of the odonate diversity found in bogs and fens may also be found in slow moving streams. Racket-tailed Emerald (Dorocurdulia libera), Ski-tailed Emerald (Somatochlora elongata), Dot-tailed Whiteface (Leucorrhinia intacta), Ashy Clubtail (Gomphus lividus), and a few damselflies notably the Spreadwings (Lestidae), Broadwings (Calopterygidae) families. Plant life in slow streams may include duckweed, ferns, mosses, cardinal flowers along with algae mats.

Seeps are natural water sources where freshwater from below the ground flows to the surface to form small streams.  These habitats often consist of a thin film of water that barely flows over rock surfaces, sometimes with a covering of leaves and moss.  Seeps can be found in forests, old pastures or fields, but are often located along hillsides or at the base of mountains where groundwater can be observed leading from crevices of rocks.  Seeps usually remain wet all year, but in extreme droughts may dry up.  Seeps create valuable habitat for a variety of rare plants and animals.  Seeps are home to some of our most threatened species of odonates such as the Spiketails (Cordul and Petaltails.

© 2021 Sheryl Chacon Search