Coleoptera (beetles)

above the rose beetle

Scarabaeidae Family

On the left is Melolontha melolontha, the common cockchafer or May bug. It is a member of the Scarabaeidae family. There are over 20 000 species in the world, 300 in Europe, and 89 in the British Isles. They range in size from 0.2 - 17 cm. The Scarabaeidae contain two main groups, the dung beetles (see below) and the plant-eating chafers. Chafers usually have the final segment of their abdomen just visible from above. Both groups have the characteristic lamellate club antennae formed by the last 3 - 7 segments of the antennae, this can be clearly seen in the photographs of dung beetles below. Usually the adults have short, strong legs useful for digging. Scarabid grubs (see the drawing below left) usually develop in the soil and feed on roots (chafers), or are found in dung or decaying organic matter. And they are always the characteristic "C" shape.

The cockchafer male has a shorter antennae club than the male. They range in size from 20 - 35 mm. Although very large and heavy they do fly, and the drawing above left shows the position of the front wings during flight, and top left at rest. When they fly they make a buzzing noise which can be alarming, but they are harmless. Their flight speed has been recorded as 3.0 metres per second with a wing beat of 46 per second. Compare this with other insects. The adults eat flowers and foliage. The female deposits her eggs about 15 cm below the soil surface. The larva, see below left, eat plant roots, with grass roots being preferred. They feed near the surface during warm months, and become inactive during winter. They live on this diet for three - four years before digging a burrow and pupating in an oval cell about 60 cm deep in the soil, see left. Pupation takes a month, but the adult will remain in the pupation cell until spring. The drawing below left is of a three-year-old larva. The larvae are sometimes called rookworms as rooks are supposedly fond of eating them. The adult beetles emerge from the soil around May, which is why they are also known as May bugs. They are found in Europe and temperate areas in Asia.

Below left is Cetonia aurata, the rose beetle, or rose chafer, another Scarabaeidae. Cetonia aurata is a brilliant golden green above and coppery underneath, though the colours can vary. The elytra have irregular transverse white streaks. The larva feeds on plant roots, humus and rotten wood especially beneath elm stumps, and can be considered a pest. The adults fly from April until September and are commonly found in flowers. They range in size from 14 - 20 mm.

Below right is a preserved specimen of an adult male Xylotrupes gideon, rhinoceros beetle, elephant beetle. They are found in South-East Asia and Northern Australia, but now can be found in captivity worldwide as they make popular pets. The adult length is very variable 35 - 70 mm. All are black and very shiny. Only the male has the two-pronged horn on his head. He uses it to knock other males out of the way when he smells a female. When disturbed adults can make a sound that has been described as a hiss or a squeak. This is made by rubbing the abdomen against the elytra (wing cases). After mating the female lays around 50 white eggs in decaying vegetation. Adults are nocturnal.

On the left is the larva of Pachnoda marginata, Scarabaeidae, sun beetle, and that is the adult. These are sold as pets and are quite easy to rear if kept at room temperature. The grubs are also reared to be fed to reptiles.

Below right is an adult Aphodius sp., showing the typical dung beetle shape - the strong, digging legs, shovel-like head and lamellate antennae,

Though beetles in the Geotrupes genus are large and heavy-looking they can and do fly both during the night and day. The adults emerge from the soil on warm nights and take flight in search of manure. The beetle on the left was found lying dead on some steps in Rhodes. It is probably Geotrupes stercorosus, a dung scarabid commonly found on the island. The adults mate in spring then the male and female dig a tunnel below the dung (they prefer the dung of herbivorous mammals, and work fast enough to bury almost a whole cow pat in a single night). The tunnel is around 40 - 60 cm deep and branches at the end into 4 - 6 chambers. In each chamber an egg is laid. Then the adults drag dung down and fill the chamber with it. The parents supply the growing larva with fresh dung. The larvae usually take just over a year to develop, so the lifecycle takes 2 years. Geotrupes adults also dig shallower tunnels to store dung for their own consumption. Beetles in the Geotrupes genus are always black with a metallic lustre.

The ancient Egyptians associated the ding ball rolling behaviour of the adult beetles with their sun god whom they believed rolled the sun across the sky,