March 5th, 2007
aquatic invertebrates – part one
Yes, it’s still winter. And no, I didn’t see these on the weekend. However, just as some people enjoy poring over seed catalogues while anxiously awaiting spring, I like looking through photos, anticipating what I’ll soon be seeing once the snow goes away.
Recently, the subject of bioindicators and aquatic invertebrates came up at
That brings me to this morning, pondering over what to write about today. I decided to dig up some photos of aquatic invertebrates seen while I’ve been out on past surveys. They might be of interest to some of you, and perhaps make you anxious to get out and look for some in your own area. I’ll make this a two or three part series depending on what other photos I come across in the next few days.
The top photo is of a Water Scorpion insect – from the genus Ranatra, which is part of the family Nepidae, belonging to the order Hemiptera (True Bugs). The Water Scorpion is usually found suspended upside down, floating just beneath the surface of ponds or slow-moving bodies of water. Despite the name, it really has nothing to do with scorpions — the tail end’s actual function is to assist in breathing. This creature uses its clasping front pair of legs to seize prey, which it feeds on with sharp mouthparts in the head. It has wings, but these are kept tightly folded against the abdomen. The insect is not a strong swimmer, propelling itself through various kicking and bobbing motions or by grasping nearby vegetaion. Its motions don’t seem particularly controlled. Here’s a page with more info about them if you’re curious in knowing a bit more about them.
The next creature is what is commonly known as a Fairy Shrimp. I believe this one is a species of Eubranchipus. These are tiny crustaceans that may be found in vernal pools – in this region, early May is a good time to look for them. As you can see from the above photo (click on images for larger view), they have a series of little legs that they use to propel themselves through a wave-like motion. You’ll need a magnifying lens to get a good look at them as they aren’t very large. Here’s a bit more about Fairy Shrimp from the Vernal Pool Association website.
The rest of these photos are of the aquatic larvae of the Caddisfly (order Trichoptera). This source states that there are 800 species in North America. Depending on species, most Caddisfly larvae form various kinds of cases as a refuge that provides camouflage and protection. I’ve included examples of two of the typical types of cases that may be found. The above example is made of organic debris such as bits of leaves, spruce needles, and other stuff (click on the photo to get a better look at the material). The photos below are of the other type of case which is made of tiny stone fragments cemented together with silk produced by the larvae. Often, small bits of grass or other debris are cemented together with the stone fragments. The stone fragment cases are usually found on the underside of rocks in streams. Some Caddisfly larvae are free-living and do not form cases. They are usually predatory species that move about as they search for prey.
In the two photos above, you can see the larvae sticking out of the case. They emerge to feed, but when disturbed, will pull back inside of their refuges.
As you can see from the photo below, some of these cases are incredibly intricate. The stone ones don’t usually look quite this way when you find them beneath a rock. However, if you find some empty cases, gently clean them off to reveal the beauty of these tiny marvels. If you want to know more about Caddisflies and their larvae, here’s an interesting page with photos and information.
Tags: aquatic invertebrates, Caddisfly larva, Trichoptera, Ranatra, Water Scorpion, Fairy Shrimp, Eubranchipus