A stonefly larvae collected in the Delaware River


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Larvae of Stonefly (top) Adult Stonefly (bottom)

Just thought everyone would enjoy this super fun and very educational song about insects before learning about one specific order of insects, plecoptera.

Feeding Habits

Some stoneflies are carnivores, while others find various other food sources such as algae, bacteria, and vegetable debris. They are shredder-detritovores, meaning they break down woody and leaf material to make food for themselves. Some stoneflies are scrapers; they eat algae and bacteria on the surfaces of nearby bodies of water. Other species of stoneflies are predators, feasting on smaller organisms such as auquatic arthropods. Some actually change their feeding habits as they go through larval molts and mature into adulthood.
Carnivorous stoneflies are important to a stream's ecosystem because they help keep populations of other aquatic organisms in balance, not allowing one species to completely wipe out all of the others around it. They consume prey that include midges, black flies, mayflies, and other stoneflies. Biologists view the structure of mouthparts to help identify stonefly types as well as feeding habits. A stonefly will usually feed during night hours. Some adult stoneflies (those who only live for a short period of time) do not feed at all.

Life Cycle

Stoneflies mature through a proccess called Incomplete Metamorphosis. They go through three main stages of development, but the stages can be broken down into eight when studying each change more specifically. The immature insects are called nymphs. Nymphs undergo a series of many molts which lead up to the final transformation in which the organism molts into an adult. There is no intermediate pupae stage where transformation occurs. Nmyphs look very similar to the adult form of the organism except that the wings are structered differently.

Here are two diagrams displaying the life cycle of a stonefly. Above is the simple, three step cycle, while below you will see a more complex eight step cycle.
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The following are the basic eight steps of a stonefly life cycle.
1. The egg matures into a nymph.
2. The nymph lives on the bottom growing in stages called instars until it matures. Maturity takes from three months to three years depending on what species the stonefly is.
3. As the nymph nears maturity it migrates to the edge of the stream or body of water.
4. The nymph then crawls out of the water, and up into the streamside vegetation, usually at night. Males usually emerge before females. Here in the streamside vegetation the final instar is completed as the stonefly sheds its outer shell and becomes an adult. The adult stoneflies life span can range from a day or two to a few weeks.
5. Adult Stoneflies mate either within the vegetation or on the ground.
6. Females fly out over the stream to deposit eggs into the water.
7. Female Stoneflies drop their egg sack into the water either by dropping it from above the stream surface, dipping their abdomen into the water's surface, while flying above it, or crawling across it. Some species crawl down the bank and deposit their eggs under the water.
8. The eggs drop to the stream bottom.


Stoneflies in the adult stage are brown, black, green, or yellow in color and contain light or dark patterned markings. They range from 0.19 to 1.97 inches in length (5 to 50 millimeters) and their flattened bodies have legs outstretching to their sides. The wide, large head of this insect is equipped with compound eyes ,that each have more than one lens, and chewing mouthparts which are directed to the front of their heads. The antennae act as the organism's sense organs. They are long and threadlike and protrude from the head of the stonefly.
Most species of this creature have four fully developed wings that are held flat over the back. While the stonfly is resting the wings are as long or longer than the abdomen in most cases. A few species of stoneflies contain no wing structure, or the wings they do contain are not long enough to make the insect capable of flight. The back wings are folded lengthwise and rest beneath the front wings when not in use. The ten-segmented abdomen is tipped with a pair thread-like projections that can be either short or long.
The larvae (LAR-vee), or the stonefly during it's youth stage, sometimes resembles the adult but in many species may not. Like adults, their bodies are flattened, with outstretched legs along with short, sometimes pointed wing pads. Species of this insect or oftentimes plant feeders and scavengers (SKAE-vihnjers), and have specialized mouthparts external image labium.jpg(as shown above) that allow them to scrape algae off rocks, collect small bits of plant food, shred living and dead leaves into smaller pieces, or chew chunks from leaves. Predatory larvae contain sharpened mouthparts that help them to grasp onto their prey. The larvae sometimes have simple or feathery gills which are located on their head, thorax or midsection, and abdomen. In all species larvae have a pair of segmented projections on the tip of their abdomen.

Habitat Needs

Adult stoneflies and those in the larval stage both often live in cold, streams or rivers, larvae living on the bottom of these bodies of water. Several species prefer the rocky shores of mountain lakes because of the waves that occur in these places. Although many stoneflies live in these habitats, each specific species lives in a unique location. These habitats include but are not limited to rocky water bottoms, in spaces among loose gravel, in piles of waterlogged leaves and debris, or on submerged logs. Adults can be found resting on logs or rocks, basking in the sun alongside streams or rivers. At night adults can be found in places where light is present, as they are drawn to it.
Field surveys have been done and clearly show that the nymphs of many species are associated with particular sections of a stream bed or lake shore. The specific habitat occupied depends on a variety of environmental factors such as the nature of the particle size in the water, the presence of other organisms, and local variations in water chemistry and temperature. Habitat preference often changes as the nymphs develop and also with different seasons.
Below a nymph in its rocky underwater environment can be seen scavenging for food.

Geographic Range

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Stoneflies live on every continent on Earth, except Antarctica. They can also be found living on many larger islands, not including however, Cuba, Fiji, Hawaii, and New Caledonia. There are an estimated two thousand species of stoneflies worldwide, and of these six hundred species can be found in the United States and Canada.

Ecological Role

Stoneflies are important components of many stream ecosystems throughout the world, and through this are quite beneficial to the environments that they live in.
The nymphs vary in food choice, being detritivores, herbivores, insectivores, or omnivores, and in some species the diets of nymphs shift throughout their development. They become food for larger animals in the stream including game fish, functioning as an important link in the food chain.
Adult feeding also can have an economic impact on humans. This occurs when their feeding damages the buds of fruit trees, or sometimes fish eggs and fry, which are important primary and secondary consumers in many streams.
Population levels of Plecoptera are used as biological indicators of water quality. Stoneflies are very sensitive to water quality, especially dissolved oxygen levels, so if the population of stoneflies decreases, this may mean that poor water quality is threatening the health of the aquatic ecosystem. Because many rivers and streams are present in New Jersey, stoneflies can be found here. Thry contribute to local foodchains and aquatic ecosystems in bodies of water near our homes! Local biologists (or even biology students in Mr. Ward's class) can test the quality of water in bodies of water nearby by looking for the presense of stonefly nymphs.

Mating Behavior

Stoneflies usually mate in swarms. They are often found swarming some sort of vegetation near the river or stream where they live. The vegetation can be any plants or trees found nearby, or they will sometimes mate on the ground. Males will attract their female mates by violently beating their bodies on the vegetation or ground. Some species of stonefly will mate many times, creating multiple offspring.
Below, stoneflies are shown mating. During this process, the formation of "mating balls" can sometimes occur. Mating balls occur specifically when more than one male males simultaneously attempt reproduction with one female and they pile onto and around her forming a ball. Studies have been done to show that this occurs more commonly than previously thought by scientists.

Above is a link to a podcast showing a man who creates fishing flies that look like stoneflies to catch fish with.

Here is another link to a podcast that is too long to be shown on this blog. You can learn about the relationship of stoneflies to the fishing season on the Bitterrppt River. podcast


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