The Western River Cruiser Dragonfly is a large dragonfly, the sexes are similar in coloration but the females are usually larger. The head is brown with greenish grey eyes that meet across the top of the head.
The face below the eyes is marked with yellow. The thorax is greenish-brown with fine hairs and a metallic luster. A bold yellow stripe extends diagonally from the dorsal area along each side of the thorax.
The wing vein at the front of the wing is yellow, the rest are black. The abdomen is black with yellow bands on the dorsal area of each segment. Legs on this species are unusually long.
Females in the family Macromiidae lack an ovipositor that is used to deposit eggs. Populations from the South Coast are darker. The larvae have a prominent horn between the antennae along with large eyes and long legs. The abdomen is broad, round and has high, slightly arched dorsal hooks.
Members of the order odonata are carnivorous. Adults capture prey by hawking or flying back and forth over an area. Dragonfly larvae can prey on a range of organisms like small fish, amphibian larvae, other aquatic invertebrates including their own species or those of other dragonflies or damselflies.
This species can be confused with the pacific spiketail dragonfly, the spiketail eyes meet at a single point on top of the head and those of the cruiser are broadly joined. The eyes are a blue color on the spiketail and grey to dark green on the cruiser