Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Ephemeroptera

Common name: mayflies

Overview

The Ephemeroptera, or mayflies, are a relatively small order of insects with aquatic nymphs and short-lived, terrestrial adults. Adult mayflies are small to medium-sized with two pairs of membranous wings; the hindwings are much smaller than the forewings. They are also characterized by short, fine antennae, mandibulate mouthparts and three very long filamentous cerci at the end of the abdomen. Mayfly nymphs are aquatic and have a body shape similar to the adults. Except for the pre-adult stage (subimago), the immature stages lack wings; the subimaginal stage is unique among the insects in having fully formed, functional wings. The nymphs have gills along the sides of their abdomen. Adult mayflies have an average wingspan of 15 mm, up to 25 mm. The males of many species have very long cerci which can be up to 35 mm in length.

Distribution and diversity

Mayflies occur across most Australian riparian and freshwater ecosystems. Worldwide the order comprises around 2,500 described species in some 20 broadly recognised families. Currently 112 described species, in 29 genera and nine families are recognised for Australia. However, this number probably represents less than half the number of species present with estimates of around 330 species in total.

Life cycle

Adult males and females gather together near freshwater in large numbers to form mating swarms. These swarms are often over a specific object such as a rock or tree; the site can be indicative of a particular species. Mating occurs during flight and eggs are laid on the water; they sink and become scattered along the substrate, and among aquatic plants and debris. Upon hatching, the nymphs live on the bottom, sheltering under stones or in the substrate. Development may take several months and up to a year, and can involve many moults (up to 20 or more), depending on the species. With dispersal and reproduction their sole function, adult mayflies have only a short life span, ranging from a few minutes up to a day or two, depending on the species.

Feeding

Adult mayflies lack mouthparts and do not feed. The nymphs feed by scraping algae and detritus from submerged stones and vegetation, filtering fine detritus, algae and other organic material in the water with their mouthparts and forelegs or shredding wood and leaf material. Some species are also known to be predatory on other aquatic insects such as fly (Diptera) larvae and other mayfly nymphs.

Ecology

Adult mayflies are always found near freshwater where they may be active day and night, and are often attracted to light. The larva of each species has preferences for a different type of habitat, which is influenced by factors such as water temperature, flow rate, chemical composition and light. Species are adapted to many habitats ranging from temperate creeks, pools and coastal waterholes to the melted snow of subalpine areas. However, the majority of Australian mayflies prefer cooler habitats with clear flowing water and are more diverse in mountain streams. The nymphs are often extremely abundant in streams where they are ecologically important, particularly as specialised detritivores. Mayfly nymph abundance, diversity and community composition are often used as valuable ecological indicators of water quality and for fisheries.