Volume 52, Number 1, May 2005:
Stream Ecology

Text-only version


ISSUE HOME PAGE

ABOUT THIS ISSUE
- about KSN
- about the author

IN THIS ISSUE
- introduction
- stream communities
- physical characteristics of streams
- biological features of streams
- common groups of stream organisms

Stream Ecology
by Carl Prophet

COMMON GROUPS OF STREAM ORGANISMS

It is impossible in the limited space available here to discuss all of the organisms that inhabit streams. The groups of organisms that are described here were selected for several reasons. First, they tend to be common and abundant in many streams. Next, they can easily be collected and recognized by the novice; and finally, they show special features that enable them to live in specific microhabitats within a stream community. Also, their presence or absence tells us something about the quality of the stream environment. Many types of aquatic organisms were omitted or mentioned only briefly because they require special equipment to collect and/or identify. Others, like fishes and freshwater mussels, were omitted because they have either been the subject of past issues of The Kansas School Naturalist or will be covered in future issues.

About half of the fifteen orders of insects includes some species which spend a part of their life cycles in an aquatic environment. The Odonata (damselflies and dragonflies), Ephemeroptera (mayflies), Trichoptera (caddisflies) and Plecoptera (stoneflies) are aquatic for all but the adult stage of their life cycles. These four orders of insects are well represented in the benthic macroinvertebrate community of most streams. Mayflies, dragonflies, damselflies, and stoneflies exhibit many similarities in life cycles. The egg hatches as a feeding and growth stage which in these three orders is known as a naiad. Each naiad passes though numerous instars (individual growth stages) and gradually becomes more and more adultlike. The final instar is the adult. This pattern of development is known as gradual metamorphosis.

Naiads of stoneflies, mayflies and damselflies have elongated bodies which are divided into three general regions, the head, thorax, and abdomen. Mouthparts are adapted for chewing. Mayflies are thought to be mainly herbaceous and stoneflies and damselflies are predaceous. In addition, a pair of compound eyes and a pair of antennae are conspicuous on the head. Wing buds are usually absent during the early instars but develop on the dorsal surface of the thorax in later instars. Three pairs of jointed slender legs which are adapted for clinging and crawling are attached ventrally to the thorax. The elongated abdomen is divided into numerous segments. In the stoneflies and mayflies the most distal or caudal abdominal segment usually bears two (stonefly) or three (mayfly) filaments; in damselflies these caudal appendages are modified into three leaf-like tracheal gills. Except for the last two or three segments, the mayfly naiad bears a pair of lateral gills on each segment of the abdomen. In stoneflies, a tuft of gills is present at the base of each of the thoracic legs. Naiads of some species of mayfly dig into soft sediments, but instars of all three orders can be picked from the surfaces of large rocks and other submerged objects in riffles. The flattened bodies of most species enable them to occupy the boundary layer thus preventing them from being washed away by the turbulent flow.

	Dragonfly Naiad
	Damselfly Naiad
	Mayfly Naiad
	Stonefly Naiad
Water Strider
Water Boatman
Backswimmer
Water Scorpion

Dragonfly naiads can be distinguished from other types of naiads by the absence of external gills plus, with few exceptions, their more square-shaped body. There are no caudal filaments or gills. Gills are present in a special gill chamber within the modified rectum. The labium of both dragonflies and damselflies covers the other mouth parts when folded; extended it may approach a quarter of total body length or more. Dragonfly naiads often hide in the bottom detritus and sediments but, like the other naiads may also be found crawling on submerged objects. Some species of each of these orders of insects require more than one year to complete their life cycles. Adults of the Odonata and Plecoptera are carnivorous and are relatively long-lived. Conversely, mayfly adults usually survive only a few days, or just long enough to reproduce. The presence of a diversity and abundance of the naiads of these three orders in a stream is a good indication of relatively clean water conditions.

Water striders, water scorpions, water boatmen, backswimmers, and giant water bugs are examples of Hemiptera (True Bugs) associated with aquatic habitats. In streams these hemipterans are most commonly found in pools and other areas of quiet water. The Hemiptera undergo gradual metamorphosis but, unlike the mayfly, the egg hatches into a nymph which resembles the adult except for its body size and the absence of wings. Nymphs have the same feeding habitats as the adults. Water striders run across the water surface on three pairs of long, spider-like legs. They feed on small insects that fall in the water and may even leap from the surface to capture prey. Water boatmen and backswimmers look somewhat alike. Their hind legs are enlarged and adapted for swimming in a rowing fashion. Backswimmers tend to be larger than the boatmen and as the name implies they swim through the water on their backs. Backswimmers use their piercing mouth parts to feed on small animals; and you can get your fingers stabbed if you hold them for long in your closed fist. Water boatmen are more darkly colored than backswimmers and swim upright. They feed on the bottom ooze. Both periodically swim to the surface for air and then dart back to the bottom. Giant water bugs (toe-biters) are active predators and will feed on any small animal that can be captured. The female deposits the eggs on the dorsal surface of the male where they stay until hatched. As their name implies, these bugs are large, sometimes approaching 5 cm in length. Water scorpions will usually be found just below the water surface clinging to submerged objects by the hind two pairs of legs and quietly awaiting for prey to come within reach. The first pair of legs are raptorial and extend forward. The body is slender and ends in a tube structure which when extended above the surface is used for air exchange. They resemble the better known walking stick.

Several other insect orders also include species that can be found in streams. In general, these types of insects undergo complete metamorphosis. The egg hatches as a larva. This type of feeding stage in no way resembles an adult. There is no trace of wings and compound eyes are absent. The body shape is variable but may generally be described as wormlike. The body is usually soft or weakly sclerotized. Legs and/or prolegs may be present or absent. Mouth parts are variously adapted for chewing, shredding, filtering or sucking. The final larval instar forms a pupa by constructing a protective covering or case. During the pupal stage the individual is transformed into an adult.

Larvae of the Order Trichoptera (Caddisflies) are a common and abundant example of stream benthos which undergo complete metamorphosis. Trichopteran larvae often coat the surfaces of large rocks in riffles as well as other submerged objects. Many types of these larvae are master builders, using a variety of materials to construct cases in which the individuals live. Grains of sand or pieces of plant material and detritus are cemented together to form the case. The size and shape of the case as well as the kind of construction material used to build the case are characteristic of different families of caddisflies. Not all caddisflies build a case. Some types build rather elaborate funnelshaped nets of silk which strain food particles from the flowing water, and other types are free-living. Feeding habits vary from carnivorous to herbivorous.

A hellgrammite is the larva of the Dobson fly (Order Neuroptera). These larvae are often 4-6 cm in length and can be found under large rocks in riffles. They are carnivores as evidenced by the large opposing mandibles which can give a hard pinch if your fingers get in the way. Prey is small invertebrates. The body is heavily sclerotized and three pairs of large legs are present on the thorax. The last abdominal segment bears a pair of large recurved hooks or anal legs which help hold the individual in place. The other abdominal segments exhibit a lateral unbranched appendage on each side. These larvae are sometimes used as fish bait.

Larvae of several families of the Order Diptera (flies) are common in some streams. Two groups will be mentioned, midges and black flies. Like caddisflies the dipterans undergo complete metamorphosis. Adult midges are often mistaken for mosquitoes, but unlike the latter, do not bite. Emergence is synchronized so that swarms of adults can be observed around aquatic habitats throughout much of the year. The small adult black fly is also known as a buffalo gnat, and the female can deliver a painful bite. The larval stages of these dipterans are aquatic. Black fly larvae are about 5-10 mm in length, dark colored, and the distal abdominal segments are distinctly swollen. These larvae attach to the substrate by a sucker-like disc on the last abdominal segment. They mostly inhabit clear streams and are most likely found on rocks in riffles or other reaches of relatively fast flowing water. Sometimes the larvae and/or pupae are so numerous that they appear to carpet the bottom. Two other features can be noted. There is an anterior pair of prolegs and a fanlike process on each side of the mouth strains or diverts small food particles towards the mouth. Midge larvae have an elongated body that is of uniform thickness from end to end. Prolegs are usually present, an anterior pair and a posterior pair. Many species spin silky tubes which are attached to submerged objects. The larva lives inside the tube and extends the anterior part of the body to feed. Some species burrow into the soft sediment, some are red colored due to the presence of hemoglobin and are called blood worms.

Photo caption: Caddisfly cases attached to sides of a floating log.

Whirligig beetles are familiar to almost anyone who has spent much time around streams or ponds. In streams, the adult whirligig beetles are found in groups on the surface in areas of slow currents. They have a shiny black body and rapidly "swim" about on the surface of the water in an erratic pattern yet avoid slamming into each other. Netting the adults is a challenge. The larvae which are predaceous actively move about on and within bottom detritus. The adult predaceous diving beetle, or dytiscid, is semiaquatic, which means it is not adapted for obtaining oxygen directly from the water. The adult must periodically swim to the surface to replenish its air supply. Its dark colored body has a yellowish stripe along the edge of the wing covers. The body length may reach 2 cm. The larval diving beetle is an actively hunting larva that is sometimes called a water tiger. These are but two of the many types of beetles that as either adult or larva inhabit our streams.

The examples described here just scratch the surface of the myriad organisms that inhabit Kansas streams. Many interesting discoveries await any person curious enough to wade into a stream, pick up a submerged rock or other object and carefully look at what is there. You will surely be amazed at what you see.

Planet Earth: Rivers and Lakes. Time-Life Books, Alexandria, VA.

How to Know the Immature Insects. Wm. C. Brown Co., Dubuque, IA.

Freshwater Benthos. The Kansas School Naturalist, 24(3)

Photo caption, back cover: Verdigris River riffle in Montgomery County.