Semiaquatic Riparian Aquatic Insects

Semi-aquatic predatory insects, like this Gelasticorid are often very abundant and can vector a lot of production from shallow waters to the riparian region.

Semi-aquatic predatory insects, like this Gelasticorid are often very abundant and can vector a lot of production from shallow waters to the riparian region.

It’s been a while since our last post on the blog. We’re of course very busy with our work relating to the effects of natural gas development on rivers and streams of Wyoming. Also the aquatic insects of the Henry’s Fork River (Idaho), Gallatin River (Montana), Yellowstone National Park (Montana, WY), and the Invertebrates of Utah Lake (Utah), the freshwater wetlands surrounding the Great Salt Lake, UT, and the Sabine River in Texas.

But as an aside, I would like to take a moment to plant some seeds for discussion… about the semi-Aquatic insects–which are almost always overlooked– and their importance to move energy from aquatic ecosystems to the riparian community. Although aquatic insects, plants and fishes produce a tons of biomass every year, most ecologists tend to think of the fate of this biomass only within the confines of production within the aquatic habitats they study.  However, we generally acknowledge the importance of riparian areas for birds, wildlife and plants. Semi-aquatic insects represent one important avenue by which nutrients (N, P, others) and energy (as organic Carbon) are transferred from aquatic systems to riparian/terrestrial systems. When water levels recede, or in the splash zone, small aquatic insects are often left stranded in the mud, moss, algae, or interstices of larger particles. Observant visitors to rivers will notice ground beetles, tiger beetles, spiders, and even toad-bugs like the gelasticorid pictured here hunting stranded prey stranded by receding waters.  There are often detritivores that also specialize in using these formally aquatic habitats for foraging: flies (true flies, Diptera), mole crickets, pygmy mole crickets, midges, fungus gnats, no-see-ums and others. I have personally observed predatory tiger beetles (Cicindela repanda) scavenging on small dead fish at the river’s edge on the Savannah River (GA, SC; 1997-1999).  These foraging insects often show a strong diel shift in their use of habitat and move from active foraging in the wetted sand and mud, into the vegetated riparian zone for cover. although the individual insects moving are small, they are also very abundant so through these daily movements they transfer large amounts of biomass (energy) from the river to the terrestrial environment.

Some of the adaptations these insects have undergone are impressive. The toad bug (pictured) is so well camouflaged in their natural environment they are very difficult to see–even for a trained human looking for them. Camouflage is not so unusual in the insect world. but what think is fascinating in the case of the toad bug, is that the camouflage pattern is asymmetrical. in biology… some form of symmetry is the norm and expected in the “normal” expression of genes. However, functional asymmetry is actually a field of biological study which focuses on understanding the causes and effects of asymmetrical expression of genes in symmetrical organisms. Kevin Bacon.

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