Stonefly

Scientific Name: Plecoptera

Number of Species/distribution
There are about 1700 species of stoneflies throughout the world, living on every continent except Antarctica.
  • 600 of these species exist in North America.
  • They can also be found on most larger islands, with the exceptions of Hawaii, Cuba, Fiji, and New Caledonia.
  • Stoneflies popluations found in the Southern and Northern hemispheres are quite distinct from one another.
Diet/Feeding
Stonefly nymphs have varying feeding preferences, dependent on their life stage, species and avaliable food sources.
Stonefly
  • In early stages (called instars), stoneflies tend to be herbivores or detritivores, feeding on plant material such as algae, leaves, and other fresh or decaying vegetation.
  • As they enter later instars, the nymphs of many species shift to being omnivores or carnivores. 
  • Some species become predators, swallowing their prey whole or biting off and swallowing parts of their prey. They use long filamentous antennae to track down prey.
  • Generally, these predatory Stonefly nymphs feed on other aquatic invertebrates.
  • The nymphs of many species are 'opportunistic feeders', meaning that they feed on what is around, while others may select for specific prey species or sizes. 
  • Carnivorous nymphs have specific adaptations of the mouth for grasping and stabbing prey, while herbivorous nymphs have mouthparts more appropriate for scraping and grinding.
  • As adults, very few stonefly species feed due to their short life span and concentartion on mating.  Those that do feed on algae and lichens, nectar, or pollen.
Habitat
As nymphs, stoneflies live in aquatic habitats, mainly in cool, clean, flowing waters with relatively high oxygen concentrations.
  • They prefer streams with a significant current, on rocky, stony, or gravel substrate, although there are some species that live in sandy areas.
  • They may also be found in cold ponds and lakes in the north and at higher latitudes. 
  • Nymphs live along the bottom of aquatic habitats (benthic dwelling). 
  • Adults are terrestrial and can be found near aquatic habitats with running water, resting on rocks, debris, and vegetation

Life Cycle
Stoneflies undergo incomplete metamorphosis as they do not have a puapl stage.  This involves passing through 3 life stages which are egg, nymph and adult stages.

Eggs
  • After mating, the female deposits large masses of eggs. 
  • To lay the eggs, the female flies over the water and may dip her abdomen in the water, releasing the eggs, or may drop the eggs directly into the water from the air. 
  • The female may also submerge herself into the water and deposit the eggs on the bottom of the stream.
  • Many species require only 2-3 weeks for hatching, while some larger forms require several months. 
  • Before hatching, the eggs may enter a resting phase (called 'diapauses') that could last three months to one or more years.
  • This prolonged resting phase occurs when temperatures increase, causing dry conditions.
Nymphs
  • Stonefly nymphs have between 10 to 30 stages of development (called instars)
  • They move from one stage to the next by shedding their exoskeleton (called 'moulting') over a period of 1-3 years. 
  • As the nymphs mature, wing pads appear and continue to become larger as development progresses. 
  • Generally, stonefly nymphs very closely resemble the adult stage.
Adults
  • When the nymphs reach their last instar, they crawl out of the water and moult one last time, becoming adults.
  • To find a mate, adult stoneflies settle on vegetation and other surfaces near the water. The males try to attract females by using their abdomen to drum, tap or scape on the surface of the rock or log
  • These vibrational signals are only attractive to females of the same species.
  • A nearby female who is interested will drum back, and they will continue this interaction until they have located each other.
  • During mating, egg fertilization occurs when the male transfers sperm directly to the reproductive organs of the female
  • While males will attempt to mate many times with different females, females will only mate once. 
  • Adults live for only 1 to 4 weeks.
  • In most species, the adult stage feeds but dies shortly after mating.

Role in Food Chain

Stonefly nymphs play an important role in freshwater systems, serving as a food source for various fish and invertebrate species.

Interesting Facts
  • Temperate species of stoneflies may have nymphs that overwinter, and continue to grow even when water temperatures drop to 0°C.
  • Some species can even live in temporary streams; when the streams dry out, they can temporarily suspend body growth and development, slowing down their metabolism in order to survive until moisture is restored.

Sources
Absolute Astronomy (2010). Plectoptera. Available here.
Animal Life Resource (2010). Stonflies. Available here.
Brusca, R. C, and Brusca, G. J., 2003. Invertebrates, 2nd ed. Sinauer Associates, Inc., Publishers, Massachusetts. Page 596.
Canada's Aquatic Environments (2002). Plectoptera. Available here.
DMI International Corporation (2003). LaMotte Aquatic Macroinvertebrate Insect Identification Flashcards.
Soil & Water Conservation Society of Metro Halifax (2006). Order Plectoptera. Available here.
Tree of Life Web Project (2010). Plectoptera. Available here.

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