Biology of Mayflies

The insect order Ephemeroptera, or mayflies as they are usually called, have attracted man's attention for centuries. As early as 1 675, Swammerdam wrote Ephemeri vita (212), which contains an amazingly detailed study of the biology and anatomy of the mayfly Palingenia. Mayflies date from Carboniferous and Permian times and represent the oldest of the existing winged insects. They are unique among the insects in having two winged adult stages, the subimago and imago. Adult mayflies do not feed; they rely on reserves built up during their nymphal life. They live from 1-2 hours to a few days and even up to 14 days in some ovoviviparous species. Thus mayflies spend most of their life in the aquatic environment, either as eggs or as nymphs, and the major part of this review concerns itself with their aquatic life. The nymphal life span in mayflies varies from 3-4 weeks to about 2lh years. The length of egg development varies from ovoviviparity, in which the eggs hatch immediately after oviposition, to a period of up to 10-1 1 months in some arctic/alpine species. Because of their winged adult stage and a propensity for drift as nymphs, mayflies are often among the first macroinvertebrates to colonize virgin habitats (89, 1 28, 241). However, over longer distances their dispersal capacity is limited, owing to the fragile nature and short life of the adults. Mayfly faunas on oceanic islands and isolated mountain areas are poor in species and usually restricted to the Baetidae and/or Caenidae (62). Their conservative dispersal makes them useful subjects for biogeographical anal­ ysis (62). The mayflies are a small insect order containing somewhat over 2000 valid species, which are grouped into approximately 200 genera and 19 families (102, 152). Despite their poor fossil record, the conservative dis­ persal, together with the wide range of morphological, anatomical and