Some animals are not content to stick to a single phenotype; these species, known as polymorphs, contain in their molecular blueprint the tendency to express two or more forms across a population, an ability largely unconstrained by epigenetic variables but still subject to selective forces that determine their relative frequency of occurence. Such variations, which affect one or both sexes to a random degree, may simply involve a markedly different colour pattern, longer appendages or sturdier proportions. They can also encompass subtler properties that affect one's ability to digest particular foods, resist certain parasites or mimic sympatric hosts and models. But even simple contrasts, between light and dark, or plain and peppered, can tilt the scales of survival towards individuals that find themselves born into an environment skewed in their favour. How the die is loaded may shift with the seasons or swing to the tune of industrial forces, with the victims serving as trade-offs of a predilection for genetic hedging that preserves the resilience of a species or accelerates its division at the cost of otherwise fit representatives who grow up in the wrong time or place.
Without the benefit of a full series of specimens from different localities, members of a single polychromatic taxon can at times be mistaken for distinct species. This was the case of a small dragonfly that lives in waterlogged portions of Southeast Asian jungles. In 1878, a Viennese entomologist named Friedrich Moritz Brauer described Orchithemis pulcherrima, a libellulid with a bright orange-red abdomen, from specimens collected from the southern tip of the Malay peninsula. In the same year, by chance or competition, Baron Michel Edmond de Sélys-Longchamps, a Belgian odonatologist, christened an insect of like build but with a largely black abdomen Calothemis exsudans, based on types from Singapore and Java. Subsequent comparisons yielded no discernible structural differences between the two and the junior binomial was duly expunged.
The variable sentinel thus challenges collectors of virtual specimens with a quintet of adults: males in red or blueish black plus females in dark hues as well as andochromatic colours. What determines the donning of one suit over another is unknown, but for some reason, swarthy males and scarlet females are scarce compared to their counterparts. Confined to protected clearings and dense margins in shaded woods, these dragonflies are easily distinguished from other erythraeus libellulids by their broad, flattened abdomens and slim wings, which are nearly in equal in width. Settling on low vegetation by cool waters, the males defend their territories with chlorocyphid-like face-offs and fluttery swoops before returning to their posts. Little else, save passing appetites, relieves these sentinels from their turf, for their hunting grounds, soft, sick and stable only to feet of unbearable lightness, resist intrusion and ring their guardian spirits with stockades of thorns and the sinking tread of a fey swamp thing.