Odonata (Dragonflies and Damselflies)

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Odonata (Dragonflies and Damselflies)
of the Lower Rio Grande Valley

The list of Odonata (dragonflies and damselflies) in the LRGV (Cameron, Hidalgo, Starr, and Willacy counties) includes 78 species, plus one species known from north and south of the Lower Valley and presumed to occur. This figure, representing only four counties, totals 35% of the Texas odonates, approximately 14% of North America's odonates, and the list continues to grow. Many of the Valley's odonates exhibit tropical affinities and are widespread in Mexico; thus, the Lower Valley's odonate fauna presents, along with the its plants, butterflies, birds, and other biotic elements, a distinctly tropical aspect. Comparatively few species are outlying representatives of northern groups; indeed, many species widespread in the nearby Hill Country are absent from the Lower Valley. This diversity is remarkably high, given the amount of aquatic habitat the valley has lost during the 1900s. Many of the Rio Grande’s resacas (oxbow lakes) have been filled and various sections of the river itself have been turned into reservoirs whose fluctuating wet and dry regimes often spell disaster to aquatic insects. Insecticides and herbicides, too take their toll of aquatic life. Nonetheless, these tenacious insects continue to flourish in the Valley and some of the State’s rarest insects may be found in resacas bordered by Brownsville’s residential subdivisions.

Most species inhabiting the northern portion of the adjacent Mexican State of Tamaulipas have been recorded in south Texas, the Rio Grande acting more as a dispersal corridor than a zoogeographic barrier for aquatic insects. South Texas representatives of Neotropical genera not widespread in the U.S. include Acanthagrion, Brachymesia, Micrathyria, Neoerythromma, Neoneura, Phyllogomphoides, and Tholymis. Some of the other as-yet unrecorded Neotropical odonates found in Tamaulipas are montane forms; these are unlikely to occur in the floodplain of the Rio Grande, but should be looked for further upriver.

John Abbott's range maps (see SOURCES below) were utilized to eliminate certain species of the Tamaulipan Biotic Province not known to occur in the Lower Valley. If surrounding counties were taken into consideration, a few species would be added to the list. English names were generated by Dennis R. Paulson and Sidney W. Dunkle and approved, with some modification, by the membership of the Dragonfly Society of the Americas. Common names for species recently added to the list were coined by the Common Names Committee of the DSA. Species whose U.S. range is confined to one or two counties are noted.

New species of odonates continue to be discovered in the LRGV. The LRGV has been poorly studied in regard to its odonate fauna (compared to mammals, birds, and butterflies, for example), and observers should expect this initial assessment to need amendment on a frequent basis as more attention is paid to these insects.

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DRAGONFLIES

Darners (Family Aeshnidae)

Aeshna dugesi Calvert, 1905 - Arroyo Darner

Odonata (Dragonflies and Damselflies) of the Lower Rio Grande Valley

Odonata (Dragonflies and Damselflies)
of the Lower Rio Grande Valley