Subject matter of experiments and observations of water animals in school aquarium XI (Rearing of Mayflies and Stoneflies)
Abstract
Mayflies (Ephemeroptera) exhibit a number of ancestral traits that were probably present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen. Their immature stages are aquatic fresh water forms (called "naiads" or "nymphs"), whose presence indicates a clean, unpolluted environment.
They are unique among insect orders in having a fully-winged terrestrial preadult stage, the subimago, which moults into a sexually mature adult, the imago. Typically, the brief lives of mayfly adults last only several days.
Immature mayflies are aquatic, and in contrast to their short lives as adults, they may live for several years in the water. They have an elongated, cylindrical or somewhat flattened body that passes through a number of instars (stages) - moulting and increasing in size each time.
The abdomen consists of ten segments, some of which may be obscured by a large pair of operculate gills. The abdomen terminates in a pair of, or three, slender thread-like projections.
Nymphs live in streams (under rocks) or in stagnant waters (freely in vegetation). In most species, nymphs are herbivores or detritivores, feeding on algae, diatoms, or detritus, but in a few species, they are predators of small insect larvae.
Adult stoneflies (Plecoptera) have long antennae, weak chewing mouthparts, two pairs of membranous wings, and two long tail filaments. The nymphs of stoneflies are aquatic and live in the benthic zone of well-oxygenated streams.
The nymphs physically resemble wingless adults but have external gills. Nymphs can acquire oxygen via diffusion through the exoskeleton, or through gills located behind the head, on the thorax, or around the anus.
Due to the nymph's requirement for well-oxygenated water, the species is very sensitive to water pollution. This makes them important bioindicators for water quality.
Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods. The insects remain in the nymphal form for one to four years, depending on the species.
The adults generally only survive for a few weeks. Stoneflies are very sensitive to pollution and only live in the very cleanest of streams.
In this contribution, some observations of mayflies and stoneflies in school aquaria are presented (moving, breathing, phototaxis, defence against predators, morphological differences between larvae of both orders).