Hermit beetle
Osmoderma eremita
Hermit beetles live all their lives in decaying oak and lime trees; successive generations may continue to live in the same tree for many years. Since the beetles do not disperse well, isolated populations build up in each tree; and if the trees fail to survive, the beetles may be lost. The threat of collecting is now further reducing the stability of scarab beetle populations. Scarab beetles-members of the family Scarabaeidae display many diverse forms and habits. The family includes dung beetles, the hermit beetle, and the Egyptian sacred scarab beetle. It is thought that the Ancient Egyptians believed that the earth was rotated by a giant scarab beetle in the sky, in the same way that the dung beetle rolls balls of dung. This, at least, is one theory as to why the Egyptians held scarab beetles in such high regard. Scarab beetles have short legs with flattened middle joints, and a number of species are attractively colored in metallic hues. The head has short antennae and is often equipped with spines or other projections. It is known that the scarab exudes a slightly perfumed scent, but the purpose of it is not understood. Relatives of scarab beetles include some of the largest beetle species recorded, including the goliath beetle, which is up to 5.8 inches (15 cm) long, and the distinctive tropical rhinoceros beetle, which is about 4 inches (10 cm) long. However, most scarab beetles reach an average length of only 0.6 to 1 inch (1.5 to 2.5 cm).
Rolling Balls
Many members of the family Scarabaeidae are specialized scavengers. Those that forage for dung (animal droppings) are known as dung beetles or “tumblebugs” after the way in which they roll dung balls along the ground and appear to tumble at the same time. (Some beetles just drag the dung pellets along the ground.) Typical dung beetle behavior involves finding a dung pile, removing a portion of it from the main mass, and rolling this portion into a ball that they roll along the ground. The dung ball is normally much larger than the beetle itself. A beetle measuring about 1 inch (2.5 cm) in length may roll a ball as big as about 4 inches (10 cm) in diameter. It does this while moving backward: It uses its front legs to walk on the ground while its hind legs press on the ball. The task of moving the ball may be shared between individual beetles of the same species, regardless of their sex. The dung ball is stored in a hole excavated for this purpose, and the beetles return to feed on it. The beetles also store dung in which the females can lay their eggs. The larvae feed inside it, keeping the outer crust intact before emerging as adults. Dung beetles are found on all continents except Antarctica, and the number of species per continent is roughly in proportion to the number of large mammal species present.
Timber-Loving Beetles
Although related to the dung beetles, the hermit beetle is a timber-loving species that is associated with decaying trees (they particularly like hollow trees). Host trees are usually common oaks or small-leaved lime trees, which are widely distributed across western, central, and northern Europe. Recent research using radio transmitters suggests that the beetle populations associated with each tree are more or less self-contained, and there is not much exchange of individuals from one tree to the next; for some reason the beetles do not seem to disperse very freely. Consequently, several generations may live continuously in the same tree. This makes them particularly vulnerable if the trees are cut down or the habitat altered in some way. The hermit beetle larva, or grub, also lives in the decaying wood of the same tree. The grubs of many hermit beetles can generate sounds by rapidly rubbing one part of their bodies against another. The purpose of the sound production, known as stridulation, is unclear. After spending their larval lives feeding on and developing in the rotting wood, the grubs metamorphose into adult beetles.
Endangered
Areas where oak and lime trees have existed for years are the most likely habitats for hermit beetles, but they are becoming more scarce. Many of the trees favored by hermits have a rich fauna of various other beetle species associated with them, several of which are also threatened. The hermit beetle is now believed to be endangered across its European distribution. However, it appears to be secure in southern Sweden, where it is being extensively studied. A recent report indicates that the beetles are now being openly traded by collectors using the Internet and other communications vehicles. This represents a further threat to the stability of the the natural populations of hermit beetles.
DATA PANEL
- Size: Length: 1.4 in (3.6 cm), excluding antennae
- Related endangered species: Ciervo scarab beetle (Aegialia concinna); Giuliani’s dune scarab beetle (Pseudocotalpa giulianii)
- Family: Scarabaeidae
- World population: Unknown
- Form: Beetle with dark-colored body shaped like a narrow shield
- Distribution: Western, central, and northern Europe
- Diet: Decaying timber in mature forest
- Habitat: Decaying trees: oaks and limes
- Breeding: Eggs laid in timber develop into grubs (larvae), which metamorphose into adult beetles
