45 Records

Status

Illinois River Cruiser (Macromia illinoiensis illinoiensis) is the northern form of Swift River Cruiser. This is the most common and widespread Macromia in northern and western Maryland. This species intergrades with the southern form, Georgia River Cruiser (M. i. georgina) in the piedmont, and some individuals may show characteristics of both forms. This is a common dragonfly on medium-sized creeks up to the largest rivers (Richard Orr's Dragonflies and Damselflies of Maryland and the District of Columbia).

Description

This form is rather similar to the less common Allegheny River Cruiser (Macromia alleghaniensis). Male Illinois has yellow not encircling S7, yellow band on S2 broadly interrupted laterally and dorsally, and mesotibial keels about 25-50% of segment length (shorter on Alleghany). Male Illinois only Macromia with auricles black. Females are quite difficult to separate (Dunkle, 2000). Compared to Georgia River Cruiser, Macromia illinoiensis georgina, Illinois lacks yellow antehumeral stripes on front of thorax (half-length on Georgia), and has yellow ring of S2 broadly interrupted laterally and dorsally (Georgia with complete yellow ring). Male Illinois shows yellow dorsal spots on middle abdominal segments very reduced or absent compared to Georgia. Male Illinois is the only Macromia with black auricles (Dunkle, 2000).