The cardinal beetle is actually three different species of beetles. The most common one is the Red-headed cardinal (Pyrochroa serraticornis), which is an orange-red beetle with a – duh – read head. It’s about 2 cm long and easy to spot as it kind of glows (in the closeup shot below you can see the color is kind of red metallic). The Black-headed cardinal (Pyrochroa coccinea) has a – uhm – black head and is rarer, slightly larger and its body has a deeper blood-red color. The third kind is the Scarce cardinal (Schizotus pectinicornis), it also has a black head but is less than 1 cm long.
Cardinal beetles prey on other insects, while their bright red color prevents them from being targeted by other predators because red usually means toxic in the bug world.
If you see a beetle with red wings and black underside and wonder if it’s a cardinal beetle or not, the easiest tell is to look at the antennae: Cardinals have toothed antennae. It’s often confused with the Scarlet lily beetle, which is smaller and usually found eating lily leaves.