Order Odonata

Introduction

1. Dragonflies and Damselflies
2. Greek, odous = tooth
3. Paleopterous Order. Triassic (225-208 mya) - Recent. An extinct species had a wingspan of 640 mm.
4. Suborders today:
   • Anisoptera (dragonflies)
   • Zygoptera (damselflies)
   • Anisozygoptera
5. Elongate body, powerful flight.
6. Both adults and nymphs predatory.
7. Almost all nymphs aquatic

Odonata Anatomy

Adult

Head

1. Mobile, large
2. Clypeus large with transverse sulcus dividing structure into postclypeus and anteclypeus.
3. Mandible adapted for predation - wide gape, many teeth.
4. Antenna short, bristle-like, 7 or less segments.
5. Compound eye large.
6. 3 ocelli on vertex.

Thorax

1. Prothorax small, mobile
2. Mesothorax and Metathorax fuse to form synthorax; terga and sterna small; pleura large
3. Wings similar in size and with complex reticulate-venation.
4. Legs positioned forward; adapted for grasping prey but not walking; often spiny

Abdomen

1. 10-segmented.
2. Terga large, strongly arched; sterna narrow, flat
3. Male accessory copulatory organs developed on sterna 2-3 of abdomen and distantly removed from testes.

Naiads

Head

1. Usually shorter and wider than adult
2. Longer antennae and with smaller eyes.
3. Mouthparts like adult only labium elaborated as prehensile organ (mask); palps modified for grasping (G & C p.333 [new edition - p.315])
   • Hinged between pre- and post-mentum
   • Largely covering face anteroventrally
   • Hidden under head when not in use
   • Extended by local increase in blood pressure caused by
     • Contraction of abdominal and thoracic muscles
     • Energy stored by locking mechanism in the primary flexor muscle.

Thorax

1. Wing rudiments extend over first few abdominal segments, reversed so that hind wings overly forewings.
2. Legs adapted for walking, burrowing or clinging

Abdomen

1. Zygoptera:
   • Abdomen bears 3 (rarely 2) large caudal tracheal gills, often used in swimming.
   • Gills usually lamellate but sometimes triangular in cross section or like a sac.
2. Other Suborders (Anisoptera in Australia)
   • Elaborate tracheal network (brachial basket) in gills on inner rectal wall replaces external gills.
   • Intake and expulsion of water through valves (constitute anal pyramid) guarding anus serves for respiration and rapid propulsion.

Odonata Biology

Adults

1. Fast fliers and are most easily caught when resting.
2. Typically diurnal, sometimes crepuscular and occasionally nocturnal.
3. Use sight to locate prey. Prey captured in flight.
4. Reproduction
   • Many males hold territories over suitable oviposition sites.
   • Copulation complex and unique to Odonata. (G & C Box 5.3)
   • Females may copulate a number of times, and exhibit sperm competition.
   • Males may remove sperm from other males inside female before mating. Special hooked process on male genitalia allows this to take place.
   • Males guard females after copulation to ensure another male does not remove its sperm.

Naiads

1. Usually aquatic and respire with gills.
2. Display elongate, scoop-like, prehensile labium which can be rapidly extended forward to grasp prey.
3. Nymphs from most freshwater habitats; occasionally from brackish water.
4. Some tolerate humid air; one genus in Hawaii terrestrial.
5. Diapause in eggs and nymphs is well known, and nymphal diapause may allow simultaneous emergence of adults in localities where the season favourable for reproduction is brief.
6. Food in nature depends on the position of the nymph in the environment, type of labium and the season.
7. As nymphs grow, food items become larger and more varied, mainly because nymphs retain the ability to eat small food items.
8. Voltinism (number of generations per year) shows a regression on latitude and altitude with low altitude mid temperate species being univoltine.
9. Metamorphosis hemimetabolous. Transformation from nymph to adult usually occurs at night or early morning.

Life History

1. Eggs inserted into plant tissue or scattered into water.
2. Nymphal stage lasts from a few weeks to several years, and the nymphs pass through 9-15 instars (intra- and interspecifically variable).
3. Wing cases appear after the third or fourth moult.
4. Metamorphosis commences days or weeks, even months before the final ecdysis.
   • The epidermis retracts progressively from the distal parts of the nymphal labium
   • Large pigmented compound eyes develop
   • Feeding ceases
   • Wing buds swell
   • Shortly before emergence the pharate adult (adult in the integument of the final instar larva)
     • Protrudes above water surface
     • Begins to breathe through mesothoracic spiracles.

• NCSU
• Odonata at Discover Life
• Florida
  • Odonata of Florida
  • Checklist of Florida Odonata
• FAMU on the Web
  • Checklist of Florida Odonata