Harvard University's Caribbean Insects: Thysanura
 

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Odonata

Odonata is a primitive order of winged insects that includes the dragonflies (Anisoptera) and the damselflies (Zygoptera). The term "dragonflies" is often used loosely to describe all members of the order. Enormous fossil odonates with wingspans of nearly 3/4 of a meter are known from the Carboniferous and Permian. Extant odonates range in size from under 2 cm to nearly 20 cm in wingspan. Most present-day odonate families are found as fossils as far back as the Jurassic or Cretaceous. Unlike most modern insects, odonates are unable to fold their wings flat against their back. Odonates are hemimetablous, meaning that they do not undergo complete metamorphosis, even though the adult looks quite different from the immature stages (called nymphs or naiads).

Odonates are some of the great fliers of the insect world, and they can beat their wings up to times 50 times per second. They have been clocked at speeds approaching 98 km/hr. Their extraordinary eyesight (from their eyes with up to 28,000 facets) coupled with their power and speed makes them skilled maneuverers.

Dragonflies are predaceous at all stages of their life. Nymphs will feed almost indiscriminately on any animals smaller than themselves, including insects, small fish and tadpoles. They are equipped with a rapidly extensible labium that, when not extended, looks like a mask covering the naiad’s face. The palps at the end of the labium have been modified into hand-shaped grasping structures that seize prey and bring it to the mandibles for consumption. Adults, given their exceptional aerial skills, typically feed on insects caught on the wing.

Dragonfly reproduction is extremely unusual. Males place a packet of sperm (spermatophore) on a unique structure on the underside of their second abdominal segment. Males do not have any external genitalia on the end of their abdomens, but instead have grasping structures. Males find a likely female and seize her by the head (dragonflies) or prothorax (damselflies) with the clasping structures at the end of his abdomen. The female bends the tip of her abdomen up to remove the packet of sperm from his abdomen. Females usually lay eggs during the mating flight. Females either lay their eggs directly in the water, or they place them in vegetation into which they have cut slits with their ovipositor. In most species, eggs hatch within 5-10 days; in seasonal environments, the eggs may overwinter before hatching.

Diversity:
Worldwide: Approximately 6500 species are described in 600 genera of 33 families. In the West Indies (Bahamas, Cuba, Cayman Islands, Jamaica, Hispaniola, Puerto Rico, Lesser Antilles): 105 species in 46 genera of 8 families. In the Dominican Republic: 79 species described in 36 genera of 8 families.

Collection and Preservation Methods:
The immature stages of odonates are almost entirely aquatic, with only a few terrestrial nymphs known. Nymphs can be caught with hand screens or drift nets. The cast off exoskeletons of nymphs (exuviae) are frequently to be found on vegetation relatively near the water’s edge.
Adults are also typically found near fresh water, since this is where they will lay their eggs. Dragonfly adults are notoriously difficult to catch because they are so swift and see so well. Your best bet is to try to catch them with a long-handled net while they are resting or mating. Dragonflies will often follow a set territory-prowling path. You may be able to catch them by observing their flight path and waiting in ambush. Since they see so well, you’re more likely to be successful if you swing your net from behind them. This requires that you have a very clear notion of their flight path. Good luck!

Once you have your specimen, photograph it immediately if at all possible. Colors fade very quickly following death, and no single preservation method is known that works for all species. Killing your odonate by immersion in a wide-neck jar filled with acetone is more likely to preserve color than similar treatment with alcohol. Placing your specimen in a plastic bag and refrigerating has also been reported to preserve color in many species. Characters that are important for identification are wing venation, eye position, and male genitalia. Specimens can be pinned or placed in glassine envelopes. Spread the wings of your specimen on a pinning board for best results in pinned specimens, and make sure that the legs are arranged so that they don’t obscure the genitalia located on the 2nd abdominal segment of males. For specimens stored in envelopes, pinch wings up over the top of the body and place in envelope sideways. Once dead and drained of much of their fat (from immersion in acetone), specimens are likely to lose their heads and abdomens eventually.

Economic Importance:
Odonates are generally considered beneficial because they feed on many other pest insects including mosquitoes. Occasionally, odonates come into conflict with beekeepers because odonates will feed on honey bees. Some European odonates transmit a flatworm that parasitizes poultry.

Recognizing Odonata:
Adult odonates have large eyes, long abdomens, and four densely veined, membranous wings. Antennae are short, bristle-like, and inconspicuous. Dragonflies have stouter bodies and hold their wings spread open at rest. Damselflies have widely separated eyes and very slender abdomens. Damselflies typically hold their wings above their bodies at rest.
Dragonfly nymphs or naiads can be divided into those that live on the bottom and those that live on water vegetation. Bottom-dwellers have very flattened bodies, and those that live on vegetation have more elongated, although still stout, bodies. The larvae of damselflies are long and somewhat slender. They usually bear three gill appendages on the ends of their abdomens.

Resources:

Alayo, P. 1968. Las Libelulas de Cuba. Torreia NS 2: 1-102.

Alayo, P. 1968. Las Libelulas de Cuba (Parte II: Laminas). Torreia NS 3: 1-54.

Checklist of Odonata at La Selva, Costa Rica

Corbet, Philip S. 1999. Dragonflies : behavior and ecology of Odonata. Ithaca, NY : Comstock Pub. Associates, 1999.

Needham, James G., Minter J. Westfall, Jr., and Michael L. May. Dragonflies of North America. Gainesville, FL : Scientific Publishers.

Silsby, Jill. 2001. Dragonflies of the world. Washington, D.C. : Smithsonian Institution Press.

Steinmann, Henrik. 1997. World catalogue of Odonata. Berlin ; New York.

Taxonomic key to Odonata families

Westfall, Minter J. 1996. Damselflies of North America. Gainesville : Scientific Publishers.

West Indian Odonates

Wetherbee, David Kenneth. A guide to the caballitos or libelulas (Odonata) of Hispaniola. Shelburne, Mass., D.K. Wetherbee, c1989.

 

Please browse and download our Field Guides to insect families and see our Caribbean Taxonomic Literature lists for available PDFs.

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