Dragonflies

Anisoptera. Spanish: Zurcidores, caballitos del diablo, caballitos de San Pedro, matacaballos, libélulas, aguacilas (General); chispiaguas (Colombia); matapiojos (Chile). Portuguese: Cavalos de cao, lavandeiras, lavabundas, pitos, cavalinhos de judeu (Brazil).

Dragonflies (Corbet 1962, 1980) are highly opportunistic predators that hunt singly or sometimes in aggregations, taking other aquatic insects flying over still water ponds, marshes, and the margins of lakes and streams (Young 1980). Their aerial acrobatics are spectacular; they can hover, dart forward instantly, and even fly backward with consummate ease and speed, feats rivaled by few other aerial creatures. In many species, most of their daylight hours of activity are spent on the wing, and so highly modified is the body for flying that they come to rest only occasionally to perch and to spend the night in sleep. The legs are useless for walking, forming instead a basketlike aerial sieve to "strain" insects out of the air.

Dragonflies usually oviposit while they are flying, dipping the tip of the abdomen below the water's surface as the eggs are extruded. The submerged eggs then drift to the bottom. Some have more specialized habits, including dropping the eggs in the water from some height, or directly placing them onto leaves, rocks, or mud, or inserting them into plant tissue (Paulson 1969).

Dias dos Santos (1981) records 705 species of dragonflies in 99 genera from the Neotropics, but many undescribed species are certain to exist. Most belong to the family Libellulidae. A few taxa in the southern parts of South America, such as Phenes raptor (Petaluridae), Gomphomacro-mia chilensis (Corduliidae), and the family Petaliidae, have their closest relatives in other southern continents. Dragonflies are mainly tropical, however, and the group tends to be poorly represented in the higher latitudes of Chile and Argentina. The strong flight capabilities of the adults, some of which are migratory, often carry them great distances. A few species are commonly found far out at sea, and some have colonized isolated oceanic islands. The cosmopolitan globetrotter (Pantala flavescens) (fig. 6.2a), which is capable of flying for hours at a time, has been collected on Coco Island and the mid-Atlantic Ilha Trindade.

Some Latin American dragonflies are distinctive and widespread. The following examples all belong to the family Libellulidae.

The ruby tail (Libellula herculea) is a medium-sized species (WS 8 cm) that stands out conspicuously against the vegetation on which it is often seen resting because of its brilliant, almost glowing, scarlet abdomen. The rest of the body is black. The sides of the thorax are covered with a gray pruinosity. The ubiquitous ferruginous skimmer (Orthemis ferruginea) is a dusky red-bodied, moderately large (WS 88 mm) species.

The "amber wings" (Perithemis) (fig 6.2d) are small (WS 5 cm) and have partially or completely amber-tinted wings. There may also be brown cross bands or spots on the wings. Similar in size are the "black wings" (Diastatops; fig. 6.2c) that have solid black wings and a bright to dull red abdomen.

Another conspicuous group of small dragonflies are the "butterfly dragonflies" (Zenithoptera). These resemble the black wings in size (WS 4—5 cm) and obscure wings, but there are clear streaks intruding from the anterior wing margin just beyond the halfway point which run transversely into the dark field. Also, it is the habit of the butterfly dragonflies to slowly open and close the wings while perched, in the manner of a sunning butterfly.

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