About Panagaeus cruxmajor (Linnaeus, 1758)
Panagaeus cruxmajor, commonly called the crucifix ground beetle, is a rare species of ground beetle native to Europe. In England, it is found in only a small number of locations. Its close relative Panagaeus bipustulatus is a more common species in most regions, and the two look very similar. They can be distinguished by differences in male genital structure: P. bipustulatus is smaller, has a rounded thorax, and its first antennomere is shorter and stouter than that of P. cruxmajor. In some parts of Europe, the relative rarity of the two species is reversed: P. bipustulatus is rarer, and P. cruxmajor is the more common species. Although P. cruxmajor has sometimes been classified as part of P. bipustulatus, most modern entomologists recognize it as a separate distinct species. This largely black, quite bristly beetle measures 8–10 millimetres (0.31–0.39 inches) long. It has large red spots on its wing cases that create the visual appearance of a black cross over a red background. During the day, the crucifix ground beetle shelters under pieces of wood. It is a nocturnal predatory species, and is thought to feed primarily on semi-aquatic snails. It was highly prized by 19th-century insect collectors. Charles Darwin recorded a well-known incident involving this species that occurred when he was an undergraduate at the University of Cambridge around 1828. Darwin had already collected two other ground beetles when he spotted what he called a sacred Panagæus crux major. To free a hand to collect the third beetle, he put one of the other beetles he was holding into his mouth. The beetle ejected acrid fluid down his throat, making him spit the beetle out, and he ended up losing all three specimens.
