Adults are pale green with brown legs and grow to 12 mm (0.5 in).

Adults of the sibling species C. muratensis and C. nudiventris cannot be distinguished from C. plumosus based on morphological characters.

When the larva pupate, they drift towards the surface, making them vulnerable to many types of fish.

[2] Other common predators include the common backswimmer (Notonecta glauca), common pondskater (Gerris lacustris), common toad (Bufo bufo), lesser water boatman (Corixa punctata), dragonflies, damselflies, great crested newt (Triturus cristatus), great diving beetle (Dytiscus marginalis), redstart (Phoenicurus phoenicurus), smooth newt (Triturus vulgaris), water scorpion (Nepa cinerea) and other midges such as Anatopynia plumipes.

[3] During the spring and summer, males create mating swarms which people can find quite a nuisance, though adults do not bite or feed.