Insects

Insects

Odonata (Dragonflies and Damselflies)

The list of Odonata (dragonflies and damselflies) in the LRGV includes 69 species, plus one species known from north and south of the Lower Valley and presumed to occur (Apppendix 1). 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 LRGV's odonates exhibit tropical affinities and are widespread in Mexico; thus, the Lower LRGV'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 LRGV 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 also take their toll on aquatic life. Nonetheless, these tenacious insects continue to flourish in the LRGV 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 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.

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. For example, a dragonfly species new to the U.S., Gynacantha mexicana, was first noted in the LRGV as recently as Fall 1998.

Butterflies

Long popular among naturalists, butterflies are finally beginning to attain the status and popularity associated with high profile animal groups such as birds and mammals. During the last decade, tours, conventions, photographic outings, and workshops focusing on butterfly observation and education have become more common. New field guides, videos, and close-focusing binoculars have all enhanced the public’s appreciation of these enchanting insects. Not surprisingly, the LRGV’s array of unique North American habitats attracts an extroardinary diversity of butterflies, often species typically associated with Mexico. Because of its high diversity of tropical species, the LRGV has become a Mecca for butterfly fanciers and their organized activities. Many LRGV residents now landscape with host plants that nourish caterpillars or nectar plants that feed adult butterflies, thus attracting a variety of species to their yards. From such activities, many rare strays have been detected during the past several years.

Based upon a review of existing data, the LRGV Butterfly list includes 294 species (including historic records) observed or collected in the four counties of the LRGV. An additional 10 species [bracketed] are included as dubious records but not calculated into the total. Previous lists of Texas butterflies have expressed strongly differing taxonomic opinions. In turn, these opinions effect the total species count of each list. For this reason, and because new species continue to be discovered in the state, this total must be considered an approximation. By applying a less conservative taxonomic scheme, the list would consist of more than 300 species.

The 294 species included in the LRGV butterfly list represent approximately 40% of all butterflies recorded in North America north of Mexico. Of this total, 70 species, or nearly 10% of the North American Butterfly fauna, have not been recorded for the United States outside of the 4 counties comprising the Lower Rio Grande Valley.

An additional 48 species are not known in the U.S. from more than 5 counties outside of the Lower Rio Grande Valley. Opler (1992) defines the Lower Rio Grande Valley without Willacy County, stating that "more butterfly species, more than 300, have been found in this small area than in all the rest of eastern North America!" Only Texas (the entire state) with 423 species, Arizona with 326, and New Mexico with 318 break the "300 species barrier" (California has but 250 species of butterflies).

In summary, only three states (Texas, Arizona and New Mexico) have documented more butterflies than the LRGV. Just over two-thirds of the 423 species recorded for all of Texas has been recorded in the LRGV and 70 species are exclusively from the LRGV.

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