The ruddy darter can be found almost Europe-wide but is absent from the Alps. It inhabits weedy ponds and ditches and is frequent in woodland. Adults can be seen between mid-June and September.
The ruddy darter is 34-36 mm long with a wingspan of about 6 cm; the legs are entirely black. As the ruddy darters mature the males become blood-red in color and have a red-brown thorax. The slightly smaller females have an ochre yellow abdomen and thorax; their eyes are brown.