Meet your neighbor: Get to know organisms living among us

Published 7:04 pm Saturday, July 15, 2017

Editor’s note: This column begins an occasional series on little-known organisms living among us, written by biologist Audrey Harrison, who works in the environmental lab at the U.S. Army Corps of Engineers’ Engineer Research and Development Center in Vicksburg.
Pseudiron centralis (crabwalker mayfly)

This week, I’d like to introduce you to one of the most elusive and fascinating creatures of the Mississippi River, right here in our backyard — a mayfly named Pseudiron centralis.

What a crazy name, you might think! Why do scientific names always sound so weird? Scientists usually choose names based on characteristics of the organism, the place or habitat in which it lives, or sometimes even after a person.

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Various combinations of word roots are usually combined and each organism we name is assigned to a genus and given a species epithet.

Let’s get back to Pseudiron centralis, which may refer to both its appearance relative to another mayfly.

This mayfly species lives in the river during its immature stages — its mom lays eggs into the river, and its siblings and itself hatch and live in the river for a full year or more before emerging out of the water as a sub-adult, called a “subimago” and then becoming an adult mayfly, starting the cycle over again.

Pseudiron centralis belongs to a group of mayflies sometimes referred to as “crabwalker mayflies,” probably because of their long legs and the way they walk. They are found in large rivers where they live in sand.

They require fast flowing water and you’ll soon know why. As we all know, animals have to eat and in fact, no two species in a single place eat exactly the same thing.

Each animal species is unique, and that’s why different species are able to live in a single habitat.

That’s called resource partitioning, a form of niche partitioning.

Some animals have very specific diets and only eat one or two types of food. Pseudiron centralis is one of these.

Remember how Pseudiron lives in sand in high flows? Well there’s a reason for that. This mayfly species actually takes advantage of its habitat to eat.

It has long, slender claws and uses them to anchor itself into the sand. When feeding, it positions itself with its head upstream and contorts its body into an upside down “U” shape.

When it does this, it creates an eddy or vortex in front of it and this removes the sand, uncovering other organisms hiding there. Quickly, Pseudiron devours these organisms, mainly midge larvae that are also unique to this habitat. This behavior was documented in a study by Daniel Soluk and Douglas Craig in 1990 (read more: Digging with a vortex: flow manipulation facilitates prey capture by a predatory stream mayfly. Limnology and Oceanography, Vol. 35: 1201-1206).

Pretty amazing for a little insect less than an inch long, right? Read this series and let me introduce you to many other neighbors you may have never heard of. I hope you enjoy!
Audrey Harrison is a wildlife enthusiast and graduate student in biology at the University of Mississippi and works in the environmental lab at ERDC. You may reach her at