Libellula composita is a medium sized dragonfly with a white face, white eyes, white costal veins, an amber spot at each wing base, and wing nodus and black stigmas. The front of the female’s thorax is brown, her sides are white and her abdomen is black with interrupted dorsolateral yellow stripes. In males, the thorax and the base of the abdomen turn pale blue, while the rest of the abdomen turns black. The larva has no lateral spines on abdominal segments 8 or 9 but has brown dorsolateral stripes on segments 7-10. The total length is 1.65-1.88 in (42-48 mm); the abdomen is 1.10-1.29 in (28-33 mm); and the hindwing is 1.29-1.45 in (33-37 mm).
Found in scattered localities (known only from 14 counties) in arid Great Basin, from southeastern Oregon to northern Utah, south to eastern California and southern Arizona and New Mexico, and also found in Texas and Kansas.
In hot springs the adults oviposit directly into the hot water, and the larvae live in cooler spring runs. The larvae overwinter and the flight season is mid June to late August.
The adults forage in brushlands, and as adults and immatures they are invertivores.
They can be found in ponds and streams with emergent vegetation, usually spring fed, sometimes alkaline, in open arid country. They can also be found in hot springs in the northern part of their range. The nymphs live among the muck at the bottom of ponds and stream pools.