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Inbiology, anymph (fromAncient Greekνύμφαnūmphē meaning "bride") is thejuvenile form of someinvertebrates, particularlyinsects, which undergoes gradualmetamorphosis (hemimetabolism) before reaching its adult stage.[1] Unlike a typicallarva, a nymph's overall form already resembles that of the adult, except for a lack of wings (in winged species) and the emergence of genitalia. In addition, while a nymphmoults, it never enters apupal stage. Instead, the final moult results in an adult insect.[2] Nymphs undergo multiple stages of development calledinstars.
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Many species ofarthropods have nymph stages. This includes theinsect orders such asOrthoptera (crickets,grasshoppers andlocusts),Hemiptera (cicadas,shield bugs,whiteflies,aphids,leafhoppers,froghoppers,treehoppers),mayflies,termites,cockroaches,mantises,stoneflies andOdonata (dragonflies anddamselflies).[3]Arachnids such asspiders,mites, and ticks also have nymphs.
Nymphs ofaquatic insects, as in the Odonata, Ephemeroptera, and Plecoptera orders, are also callednaiads, anAncient Greek name formythologicalwater nymphs. Some entomologists have said that the terms larva, nymph and naiad[4] should be used according to the developmental mode classification (hemimetabolous, paurometabolous orholometabolous) but others have pointed out that there is no real confusion.[5] In older literature, these were sometimes referred to as theheterometabolous insects, as their adult and immature stages live in differentenvironments (terrestrial vs.aquatic).[6]
In 1628, English physicianWilliam Harvey publishedAn Anatomical Disquisition on the Motion of the Heart and Blood in Animals. In his writing, Harvey hypothesized that the pupal stage in insects was the result of imperfect eggs.[2] While some eggs produced smaller versions of fully-matured insects known as nymphs, others created intermediate forms. Thus, these intermediate forms must go through a second egg stage to reach their adult form. This hypothesis attempts to explain the developmental differences between hemimetabolous and holometabolous metamorphosis. Though an outdated hypothesis, it was still significant towards the modern understanding of nymphs.[7]
Infly fishing with artificial flies, this stage of aquatic insects is the basis for an entire series of representative patterns for trout.[8] They account for over half of the fishing fly patterns regularly used in the United States.
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