Order Ephemeroptera

Introduction

1. Mayflies
2. Greek, ephemeros = lasting a day; pteron = wing
3. Paleopterous insects related to Paleodictyoptera
   • Permian to recent
   • Paleodictyoptera: fossil forms - Upper Carboniferous - Permian
4. Most primitive order of extant winged insects.
5. Soft-bodied, elongate insects.
6. All nymphs aquatic
7. Fossil record from Permian (286 mybp) to Recent.
8. Between 1,000 and 2,000 modern species, cosmopolitan.

Ephemeroptera Anatomy

Adult

Head

1. Adult mandibulate mouthparts vestigial, not functional or strongly sclerotized.
2. Compound eyes large, eyes of males usually divided into dorsal and ventral sections. Some males have the upper section greatly expanded but constricted at its base. Such eyes are called turbinate eyes.
3. Three ocelli.
4. Antenna shorter than head; filiform, multisegmented.

Thorax

1. Prothorax small; mesothorax, metathorax fused.
2. Wings membranous.
   • Wings held above thorax at repose.
   • Wing fluted (like an open fan)
3. Forelegs sometimes vestigial; male forelegs elongate and sometimes adapted for grasping female.

Abdomen

1. 10-segmented
2. Cerci elongate, multisegmented.
3. Usually with appendix dorsalis, hence 2 or 3 caudal filaments.
4. Females with paired gonopores along posterior margin of sternum 7.
5. Male often with segmented genital appendages and double penis.

Nymph (or naiad)

Head

1. Hypognathous or prognathous
2. Eyes large, three ocelli present.
3. Larval mouthparts mandibulate, adapted for chewing.
4. Mandible with three articulations (remember that Ephemeroptera belong to the Dicondyla, which are suupposed to have only two mandibular articulations).
5. Gills present at the base of the maxillae in some groups.

Thorax

1. Gills present near the base of the coxa in some genera.
2. Femora flattened usually
3. Tarsi usually unsegmented and with claw single.

Abdomen

1. Abdomen 10-segmented, gills present on segs. 1-7, either lateral or dorsal.
2. Gill form variable, often 1st pair different from the remainder.
3. Abdomen of all stages with 2 or 3 long caudal filaments (cerci and terminal filament).

Ephemeroptera biology

Adults

1. Short-lived, do not feed.
2. Swarming behaviour sometimes astounding.
3. Usually seen near water on vegetation and other objects; occasionally attracted in large numbers to lights.
4. Air in alimentary system of adult affects flight behaviour.
5. Aerial copulation.
6. Eggs deposited in water (500-3000 per female).
   • some attach to rocks by filaments.
   • Gelatinous egg masses produced by some groups
   • A few species are ovoviparous.
   • Hatch within a few weeks.

Naiads

1. Aquatic with abdominal gills at junction of segments 1-7.
   • Lamellate gills of species in moving water.
   • Plumose gills of species in standing water.
2. 10-50 larval instars, depending on diet and temperature.
3. Found in fast-flowing streams or still waters of ponds where some species burrow into bottom muck.

Metamorphosis

1. Hemimetabolous
2. Long life as a nymph. One generation per year usually; some with one generation each 2-3 years
3. Subimago unique developmental stage - stage between last naiad instar and adult. Only insects with ecdysis following acquisition of functional wings.
   • Body surface of subimago is covered in microtrichia or microspines which adults lack almost entirely. Microtrichia thought to provide hydrofuge function for subimago emerging on water surface.
   • Forelegs, caudal filaments, male genitalia and eyes not to full size in subimago.
   • Subimagos generally slower flyers than adults, weight loss of 25% (mostly water) to adult.
   • Subimago and adult cuticle preformed and folded down in mature larva.
   • Two distinct durations for winged stages:
     • 8hr-2day subimago, adult 1-3days (rarely to 14 days) - considered basal.
     • Subimago few minutes and adult a few hours - considered advanced.
     • evolved independently in at least 9 lineages. In four of these lineages
       • The female adult is eliminated entirely, remains as a pharate instar inside subimago,
       • Mate as subimago.
       • Males never mate as subimago because male genitalia not fully formed.
4. Trend in mayfly evolution towards minimisation of terrestrial portion of lifecycle.
   • Subimago functions for habitat transition
   • Microtrichia may also be used to help unfurling of wings in ecdysis

thanks to University of Queensland

• NCSU
• Ephemeroptera
  at Discover Life
• Florida
  • Mayflies of Florida
    USGS
• FAMU on the Web
  • Ephemeroptera Galactica
    Site for mayfly researchers
  • Mayflies (Ephemeroptera) of the Southeastern United States