Comentarios sobre caballitos del diablo (género 'Lestes') - Comments on damselflies (genus 'Lestes').

The order Odonata includes the suborders Anisoptera and Zygoptera. The suborder Anisoptera includes the species known as dragonflies and the suborder Zygoptera includes the species known as damselflies.

The suborders differ in two major characters. In Anisoptera, the head is no wider than the thorax in dorsal view and the hind wings are wider at the base than the forewings. In Zygoptera, the head is wider than the thorax and the hind wings are similar to the forewings in basal width and orientation of the quadrangles.

Although the term "dragonfly" is typically used for the entire order Odonata, some authors restrict this term to the suborder Anisoptera and use "damselfly" for the suborder Zygoptera.

I once wrote about two dragonflies of the family Libellulidae of the suborder Anisoptera, specifically the genera Erythemis and Erythrodiplax. This time I will comment on damselflies of the family Lestidae of the suborder Zygoptera, specifically on the genus Lestes. The photographs correspond to a species that I did not identify of the genus Lestes.

Members of the genus Lestes can be found along the gradient of freshwater habitats, from vernal pools that dry up annually in early summer, temporary ponds that dry up in late summer in some, but not every year, and permanent bodies of water.

All damselflies are univoltine (only one generation per year) and most overwinter as desiccation-resistant eggs with diapause (delayed development in response to regular and recurring periods of adverse environmental conditions), which are followed by a short larval stage of approximately 2 to 3 months in spring and early summer. During this larval period they pass through 10 instars. Species with this life cycle are L. congener, L. disjunctus, L. dryas, L. forcipatus, L. rectangularis and L. unguiculatus. This mode of life permits these Lestes species to potentially inhabit any position along the freshwater habitat gradient, except for the most vernal ponds. Only the species L. dryas appears to have a short enough larval period to successfully emerge in vernal ponds that dry out after only a few weeks in spring and early summer.

The exception to the typical life history strategy of Lestes is given by the directly developing eggs of the species L. eurinus, L. inaequalis and L. vigilax. In the case of these species, the eggs hatch soon after laying, in late June and July, and their aquatic larvae are present until May of the following year. Therefore, their requirement to overwinter as aquatic larvae instead of diapausing eggs restricts them to permanent water bodies (they can be found in temporary water bodies that have not dried up for several years).

There are species with the ability to survive climatic extremes such as winter. The species L. unguiculatus, L. disjunctus disjunctus y L. dryas overwinter as eggs at a late stage of embryonic development. The embryos enter diapause in September and, in this condition, can survive exposure to temperatures as low as -20 °C. Post-diapause development can take place at 0 ºC, but does not occur until the eggs are wetted as the pond fills with runoff water in the spring. Hatching in L. disjunctus and L. unguiculatus is highly synchronous and occurs when the water temperature is about 10 ºC. Larval development is completed in about 60 days and emergence is highly synchronous and is completed in about 10 days. It should be noted that these species lay eggs only on green stems of aquatic plants of the genus Scirpus, between 5 and 60 centimeters above the water surface and the stems selected are those growing in small groups or those bordering larger groups.

All these variations in the life history of Lestes species related to different distributions along the gradient of freshwater habitats and climatic conditions are due to adaptations to habitat and predators present in the habitat. In relation to predation, Lestes species only respond to the presence of predators with which they coexist. All species decrease their movements and responsiveness to prey in the presence of coexisting predators; these behavioral responses decrease their conspicuousness to predators and thus increase their survival when predators are a threat.

If a species lives in ponds without predators, for example fish, and is placed in a pond with fish, the species will show no behavioral response to predators to move away if one approaches and will die from predation because it lacks adaptive behavioral responses to reduce predation.

Finally, the genus Lestes is prone to form heterospecific pairs, that is, pairs formed by individuals of different species but of the same genus, for example, a male of L. sponsa and a female of L. barbarus. In this regard, it has been suggested that in cases where females are fewer in number than males and their arrival in the breeding environment is unpredictable, it is more advantageous for a male to grab any female that resembles a female of the same species than to wait for a precise identification.

Images captured with Panasonic DMC-FH4 digital camera.