Cafius luteipennis is the smallest of the common Cafius species that occupy kelp wrack on local sandy beaches. They have a size range of 7.0mm to 8.5mm and are the least robust in figure. They are most common in early spring to early summer during foraging at night, and can be seen in large numbers coinsiding with C. lithocharinus. Their distribution is the mostly patchy on all beaches. Golden, iridescent elytra are the distinguishing feature and are easily seen when exposed. They mainly consume fly larvae and small numbers of adult flies, though they are known to predate on smaller amphipods. Phoretic mites and nematodes are found in varying numbers under their elytra. Research on these beetles is limited, possibly due to the infrequency of their occurrence and the difficulty in finding patches of kelp with large enough numbers.