This species is most likely to be confused with the Red-veined Darter (Sympetrum fonscolombei) and the Common Darter (Sympetrum striolatum) however the latter is more orange-red and has a straight sided abdomen and yellow stripes on the legs, while for Ruddy Darter, the legs are all black. Female Ruddy Darters are similar to female Black Darters (Sympetrum danae) however in the former there is no black triangular marking on the thorax. 
 
 

The male have the head, thorax and abdomen vivid red, and become blood-red with maturity with a red frons and red-brown thorax. There is a very noticeable constriction of the abdomen around S4, giving a club-shaped appearence.

Females are slightly smaller, have a golden-yellow colour with black markings. The abdomen widens for the final third of its length and shows a marked pinched section where it joins the thorax. There is no red panel on the side of the thorax. Older females may develop some red along the midline and segment boundaries of the abdomen.
 
 

Mating takes place on the wing, with the coupled pair performing a dipping flight over the water. The female jettisons her fertilised eggs at the water surface by alternating movements of the abdomen. The male will hover nearby during this period and protect the female by driving off any approaching males. Females oviposit usually when in tandem with male, over open water, clumps of plants or exposed muddy margins by dipping abdomen on water surface to wash off batches of eggs.

Eggs either hatch within a few days of laying, or if laid late in season eggs will diapause until spring. Larval development takes one year beneath the water surface. Larvae live amongst roots of aquatic plants including Typha and Equisetum. Emergence on vertical plant stems in early morning.

Preferred environment are shallow well-vegetated lakes and ponds often in woodland. In Ireland associated with pools in fens and cutover bogs, small base-rich mesotrophic lakes and turlough-like lakes. Flight period from mid June to mid October.