Out of the four Cafius species on the beach, Cafius seminitens is the largest ranging 8.5mm to 14.5mm. C. seminitens is also the second most common Cafius on the beach, next to C. canescens. During summer months, these beetles can be found commonly at night along with C. canescens, in wet ot dry kelp. These black beetles typically contain bright pewter (silver) hairs that run down their body, which is a distinguishing feature. They, like all larger rove beetles on local beaches, prey on smaller arthropods, but usually prefer dipteran (fly) larvae. Phoretic mites and nematodes have been known to occupy their wings and elytra in large numbers and moderate frequency. Cafius seminitens sometimes carries a species of parasitic fungus, Laboulbenia philonthi (described in Thaxter 1893), which has a very low impact on the actual health and fitness of their host. Overall, Cafius seminitens is one of the most abundant arthropod predators, providing a unique opportunity for research, such as descriptive taxonomy (Orth and Moore 1980), larval descriptions (James, Moore and Legner 1971), phylogeny (Jeon, Song and Ahn 2011) and unique adaptations (Topp and Ring 1988).