Dragonflies And Damselflies

Odonata.

These are familiar insects, always found near water, although the powerful and untiring wings of dragonflies may take them on long journeys. They are easily recognized by their elongate bodies, four similar, many-veined wings (with a dark spot on the leading edge near the tip, the pterostigma), and bulbous eyes with an enormous number of minute ommatidia. Between the eyes arise the tiny, bristlelike antennae. The thoracic segments are angled obliquely so that their dorsal surfaces form an incline.

Dragonflies are distinguished from dam-selflies principally by their more robust and usually larger bodies and their habit of extending the wings out to the sides when at rest. Some damselflies are also large, but they are always slender. Most damselflies fold their wings together back over the abdomen when not in use. The wings are also abruptly narrowed and slender at the base in contrast to the broadly based dragonfly wings. The nymphs of dragonflies are also more heavily built than those of the damselflies. The former have a broad, tapering abdomen, tipped with short spinose processes (fig. 6.2b); their gills are located internally in folds of the rectum. Damselfly nymphs have elongate, slender abdomens, bearing three, conspicuous, finlike terminal gills (fig. 6.3b, e).

The body and wings of odonates are very often highly decorated with bright or gaudy colors. The tints of the body are transient and quickly disappear from dead specimens; but those of the wings persist as spot and band patterns or broad fields, most often over the basal half or third of the wing. In some, the entire wing may be colored, often in glossy red, orange, or

Figure 6.2 LIBELLULID DRAGONFLIES (LIBELLULIDAE). (a) Globetrotter (Pantala flavescens). (b) Globetrotter nymph, (c) Black wing (Diastatops dimidiata). (d) Amber wing (Perithemis indensa)■

blue. The coloration of the male frequently differs from that of the female, and it is sometimes difficult to know they are of the same species until they are seen copulating.

During the pairing process, the sexes are peculiarly joined in a tandem configuration unique to this order of insects. The male's copulatory structures (genital fossa) are situated on the undersides of the second and third abdominal segments at a considerable distance from the true sexual aperture at the tip of the abdomen. Prior to mating, he transfers spermatozoa from the gonopore to the penis in the fossa. During mating, the male grasps the female behind the head (dragonflies) or thorax (damselflies) with his strong, tonglike cerci while she bends her abdomen forward to the fossa and receives the sperm from the penis. Couples fastened together in this manner are commonly seen resting on vegetation by the water's edge, or even in flight.

Adult biology, such as flight patterns and competition for prey and hunting space, in Latin America has not been well studied but is generally the same as that observed elsewhere. Some special adaptations for surviving dry periods have been noted (Morton 1977).

Immature odonates are all aquatic, the nymphs being found in all sorts of running and still water environments: ponds, shallow stream and lake margins, stream pools, tree holes, and tank plants. The nymphs are insectivorous. They capture prey with a mantislike grab of the enlarged and elongated, extensile lower lip (labium). The nymphs show structural adaptations in response to the diverse ecological niches they occupy, but these are less extreme than those of mayflies. Burrowers tend to be short and broad, bottom sprawlers flattened and long-legged (fig. 6.2b), and •Wimmers slender and streamlined. Probably only about 15 percent of the immatures Of the Latin American species are known.

The literature on Latin American odonates is reviewed by Dias dos Santos (1981) and Paulson (1977, 1982). A species list is provided by Davies and Tobin (1984-85).

References

Davies, D. A. L„ and P. Tobin. 1984-85. The dragonflies of the world: A systematic list of the extant species of Odonata. 2 vols. Int. Soc. Odonatologia, Utrect. Días dos Santos, N. 1981. Odonata. In S. H. Hurlbert, G. Rodriguez, and N. Dias dos Santos, eds., Aquatic biota of tropical South America. Pt. 1. Arthropoda. San Diego State Univ., San Diego. Pp. 64-85. Morton, E. S. 1977. Ecology and behavior of some Panamanian Odonata. Entomol. Soc. Wash. Proc. 79: 273. Paulson, D. R. 1977. Odonata. In S. H. Hurlbert, ed., Biota acuática de sudamérica austral. San Diego State Univ., San Diego. Pp. 170-184.

Paulson, D. R. 1982. Odonata. In S. H. Hurlbert and A. Villalobos Figueroa, eds., Aquatic biota of Mexico, Central America and the West Indies. San Diego State Univ., San Diego. Pp. 249-277.

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