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INTRODUCTIONOdonata, or dragonfli es, constitute a small, well known, widely distributed order of insects. The 5000 or so species belong to three suborders (all referred to here as dragonflies): the Anisozygoptera, containing only two known species; the Zygoptera; and the Anisoptera. Typically large and active by day, the winged adults are conspicuous at ponds and rivers, which usually form the encounter site (see 155) or "rendezvous" (30) where repro ductive behavior takes place. Accordingly, dragonflies provide valuable models for interpreting the behavioral interactions of many other insects that assemble for mating but are less readily watched in the field.Two books treat the biology of the order: the first (201) emphasizes systematics and functional morphology, and the second (30), ecology and behavior. This article is a review of the main features of the dragonfl y life history and so can be regarded as a highly condensed supplement to the second of these books. Accordingly, I give prominence here to research published after 1960, and have not cited sources for information already reported in the second book (30).A topic not reviewed but which deserves mention here is the growing extent to which faunistic records are being used as source material by scientists who are trying to check or mitigate habitat destruction and species extinction by recommending the creation of nature reserves (e.g. 4, 136, 186, 225). As freshwater insects, dragonflies are exceptionally vulnerable to urban and agricultural expansion, which commonly entail the draining of ponds and marshes. HABITAT SELECTIONImmediately after emergence, adults typically fly away from water, not returning until reproductively mature, several or many days later. At this

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In aquatic insects, emergence (ecdysis to the adult or subimaginal stage) varies widely in temporal pattern. The comparative study of this pattern is feasible and informative in orders such as Plecoptera, Ephemeroptera, Odonata, Diptera and Trichoptera in which all members of a population pass through the water-surface when emerging. Methods by which emergence rate can be measured are discussed. Four basic temporal patterns of emergence exist. Emergence may be (1) continuous with irregular fluctuations in rate; (2) rhythmic, with a lunar period; (3) sporadic, occurring at irregular intervals of a few days; or (4) seasonal. Examples of each of these patterns are given, and reference is made to the proximate and ultimate environmental factors which may be maintaining the patterns observed. Diurnal rhythms of emergence are excluded from consideration. When emergence is restricted seasonally in temperate latitudes, the degree of its synchronization within the emergence period varies widely but is usually constant and typical for a given species. This has provided the basis for an ecological classification of British Odonata, the validity of which is examined in the light of recent research.

We revisit the hypothesis, first advanced in 1962, that, with regard to their means of thermoregulation and overt behaviour, two types of Odonata can be recognised: fliers, when active (during reproductive activity, primarily, or foraging) remain on the wing, whereas perchers, when similarly engaged, spend most of the time on a perch from which they make short flights. First, in light of the available data, we restrict the hypothesis to apply primarily to activity at the rendezvous. Next, we review evidence, including direct measurements of body temperature coupled with activity budgets, to test the proposition that the hypothetical classification constitutes a dichotomy rather than a continuum. We conclude: (1) that there is merit in retaining the dichotomous classification into fliers and perchers, together with the thermoregulatory capabilities assigned to each category; (2) that the distinction between fliers and perchers is sufficiently discrete to be a useful predictor of the suite of thermoregulatory strategies and energy demands characteristic of representatives of each category; and (3) that, within each category a continuum exists such that the capacity to heat the body by irradiation (i.e. ectothermically) or by metabolic heat production (endothermy) increases with body size. Some departures from expectation based on the percher/flier dichotomy reflect the increased flight activity that occurs at the rendezvous under conditions of heightened conspecific or interspecific interference. Other apparent anomalies are identified as topics for potentially fruitful research.THE FLIERfPERCHER TEMPLATE Forty-six years ago Corbet (1962) hypothesised that, with regard to their means of thermoregulation and overt behaviour, two types of Odonata can be recognised. Fliers are those that, when active, remain on the wing, whereas perchers, when active, spend most of their time on a perch from which they make short flights (Corbet 1962). At the time this difference was rationalised in terms of the dragonfly's need to avoid overheating the body, although this reasoning was based on little more than the inference that, by flying persistently, fliers would be tending to maintain the body temperature at a high level unless they possessed some 'special' compensating