Life Histories of Waterstriders of the Sangamon River,
Champaign County, Illinois
 I'm studying the life histories of several species of waterstriders and kin on the Sangamon River at Mahomet, Illinois. This work presently consists of collecting samples of waterstriders on a weekly basis for later identification. Species in the genus Rheumatobates (Gerridae) and the waterstrider Metrobates hesperius (Gerridae) are the primary focus, but I am also collecting other species including the riffle bug Rhagovelia oriander (Veliidae) and, in the early spring, the genera Gerris and Aquarius (Gerridae).
The map shows my study area. The blue line is the Sangamon River passing through downtown Mahomet. The blue arrow indicates the direction of flow. The blue dot is where I put my boat in the water. The large red dot with the number is an old (inactive) USGS gauaging station. The thick pink lines are the upstream and downstream limits of my study area. The drainage basin at this point on the Sangamon River is about 362 square miles, with land use dominated by row crop agriculture.
One interesting thing about this project is the size of the river. It is too large and deep to be sampled by wading in the water (in the spring of 2000 there were two drownings further downstream in the river), yet too shallow and snag-filled to allow motor boats -- so I sampled from a much smaller boat, a kayak. An added advantage of this approach is that it allows me to pursue larger adult waterstriders, such as Metrobates hesperius and Aquarius nebularis, which tend to quickly move away from the shoreline when disturbed.
The Sangamon River is fairly heavily shaded in my study area, and dappled sunlight filters through the leafy trees in the summertime.
Mid-river on open water I find Metrobates hesperius adults and late instar nymphs from July into the fall. The nymphs, such as this late-instar individual, are surpisingly coloful.
Adult females of Metrobates hesperius can be particularly quick moving across the surface film.
A colorful adult male of Metrobates hesperius.
By mid July, adult females of Metrobates hesperius can be seen clustering energetically around leaves and other woody debris that is drifting down the middle of the river. Close examination of these leaves reveals the reason - they are ovipositing (laying their egges) on the leaves. Here is a close up view of a cottonwood leaf with the eggs on it.
A closer look at a couple of the eggs. Each egg is about 1.3 mm in length.
Along the shoreline, the exposed roots of trees shelter large populations of Rheumatobates and younger instars of Metrobates, as well as a few Microvelia american (Veliidae).
A late instar Rheumatobates nymph collected in association with the overhanging tree roots. (the middle and hind legs are chopped off in this photo - they are much longer)
Males of many species of Rheumatobates have highly modified antennae and middle and hind legs. This is an oblique view of a male of Rheumatobates tenuipes collected in association with the overhanging tree roots. Note the highly modified antennae.
Carefully checking out the water surface in and around snags is done from a boat.
Snags, resulting from trees falling in the river in the river, accumulate large mats of floating debris and garbage. Such sites are home for several genera of Gerromorphans, including the marsh treader Mesovelia mulsanti (Mesoveliidae).
Where current is swift, such snags sometimes have eddys on the downstream side of partially submerged branches (see arrow).
Upon closer examination of such eddys, I often find that they are home to the riffle bug Rhagovelia oriander (Veliidae) (the light gray flecks on the water in the image below).
An adult female of Rhagovelia oriander collected on the Sangamon River.
Sure, fieldwork can be fun! Lara Storm (in forground) was helping with the sampling one day.
Unloading boats for an afternoon of chasing water striders on the river.
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