The name cardinal beetle typically refers to three different species of beetles. The red-headed or ‘common’ cardinal beetle (Pyrochroa serraticornis) is a red to orange beetle with, as the name suggests, a red head. It is about 20 millimetres (0.79 in) long, and is found throughout Britain. The rarer black-headed cardinal beetle (P. coccinea), similarly found at sites across Britain, is larger and a deeper blood red. The scarce cardinal beetle (Schizotus pectinicornis) also has a black head, but is smaller at around 9 millimetres (0.35 in) long. The scarce cardinal is only found at a few sites in Scotland and Wales.
Cardinal beetles prey on other insects, while their bright red colour prevents them being the target of other predators which believe them to be toxic.
Red-headed cardinal beetles are normally found at the edges of woodland.Adults of this variety usually emerge around May in England, when they tend to be found under loose bark on deciduous trees. Fallen and standing timber and rotting stumps may also host this species. As the weather gets warmer, they disperse and are often found on dense, low herbage. They bask for long periods on large leaves often near water – the Grand Union Canal being one particular hotspot.