Beetles in the Scarabaeidae family, dung beetles, chafers
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 in this family, 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.
Adults. Chafer adults 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.
Larvae. Scarabid grubs (see the drawing below right) 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 female has a shorter antennae club than the male. The male's antennae end in 7 flaps that can be opened up and closed like a fan. Each flap is studded with sensory pits receptive to the chemical signal
released by the female. When opened like a fan the male has a better chance at detecting the chemical molecules. When the flaps are closed it means he is not seeking a mate. The female has only 6 flaps. The elytra (wing cases) are reddish brown. Cockchafers 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 wing cases during flight, and at rest. When they fly they make a buzzing noise which can be alarming, but they are harmless.
The female deposits her eggs about 15 cm below the soil surface. The larva, see above, eat plant roots, with grass roots being preferred. They feed near the surface during warm months, and become inactive during winter. The drawing on the left is of a three-year-old larva. They can grow up to 60 mm long. They have a shiny brown head and legs, with a dirty white body. The larvae are sometimes called rookworms as rooks are supposedly fond of eating them. 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 above right.
Pupation takes a month, but the adult will remain in the pupation cell until spring. 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.
Cetonia aurata, rose beetle, or rose chafer
On the left Cetonia aurata it 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 larvae grow up to 50 mm long, the have a brown head and legs, and a dirty white body.
The adults fly from April until September and are commonly found in flowers. The adults are unusual in that they can fly with their elytra (wing cases) closed, unlike other beetles which have to fly with their elytra open. They range in size from 14 - 20 mm.
On the right is a preserved specimen of an adult male 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.
Aphodius sp. typical dung beetle
On the right is Aphodius sp. showing the typical dung beetle shape - the strong, digging legs, shovel-like head and lamellate antennae.
What dung beetles do for us
Dung beetles perform a very necessary service to us humans with our ever increasing consumption of meat. For example, in the U. S. there is almost 1 cow for every 3 people. Each cow produces about 9 tonnes of dung a year! And how do we get rid of this dung? Well for cows reared outside we do nothing at all. The dung beetles and other invertebrates perform that service for us for free.
In Australia there are no native dung beetles, and after the introduction of cattle in the 19th century there was a massive fly population explosion because of all the piles of dung lying around. So they introduced dung beetles. This greatly reduced fly numbers, which pleased both cattle and humans.
Pachnoda marginata, sun beetle
On the left is the larva of of the sun beetle, and on the right 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.
The ancient Egyptians associated the dung ball rolling behaviour of the adult beetles with their sun god whom they believed rolled the sun across the sky, consequently dung beetles were venerated in their culture
Geotrupes stercorosus Dor beetle
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, and all over Europe. Adults are 14 - 20 mm long, black or blue/black with a metallic blue or green sheen.
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. They will also eat rotting fungi.
Right is an Ansiopa sp., these are found in central Europe. Note the lamellate antennae.
The adults live mainly on cereal and grass flowers, and the larvae on grass roots. They tend to be found on warm, dry slopes with sandy soil.