The Rambur’s Forktail
By Liam Wolff, Phinizy Research Intern
Male Nominate, Female Blue Male-Like; Photo by Liam Wolff
Male Nominate, Photo by Liam Wolff
The Rambur’s Forktail, Ischnura ramburii, is the most abundant species of damselfly at Phinizy Swamp and probably the most common wetland damselfly across the Southeast United States as a whole. Its range expands west to California into Mexico with an isolated population in Hawaii. One of the most interesting features of the Rambur’s Forktail is its polymorphic variation. Polymorphism is the occurrence of a species that displays two or more forms. These forms are determined by dominant and recessive alleles that are inherited at fertilization. Rambur’s Forktails, like many insects, demonstrate this polymorphism on top of sexual dimorphism. With sexual dimorphism, the males and females of the species are apparently dissimilar – they differ in appearance. To make things even more complicated, the color morphs are different at varying ages.
Rambur’s Female Orange, Photo by Liam Wolff
Rambur’s Female Green Male-like; Photo by Liam Wolff
Nominate form males are light green on the thorax with similar coloration on the abdomen and a blue terminal end. Nominate females tend to be olive in coloration across the abdomen and thorax. As immatures, female Rambur’s Forktails are a bright orange. There are two female morphs that are very similar to males, though. One form is bright green like the male, but the colors are less defined. The other has a green abdomen with a blue terminal segment like the male, but the thorax is a sky blue. At Phinizy, most of the damselflies we study are in their larval stage. However, at this age it is very difficult to differentiate between species. Unlike many macroinvertebrates in the Savannah River which are scrapers or filter-feeders, the suborder Zygoptera (damsels) consists of predators.
Rambur’s Female Olive; Photo by Liam Wolff