Zoologger: The beetle with a handle on its back

22 November 2012 by Michael Marshall

You don't even need to book (Image: Takashi Komatsu)

Species: Eocorythoderus incredibilis

Habitat: Hiding inside termite nests in Cambodia, letting someone else do the heavy lifting

Anyone who has ever been for a long walk with small children knows that one of them will inevitably say, or rather whine, "I'm tired. Carry me?" Male readers may well have given in and given the child a piggyback, if only to avoid being thought too feeble to carry the weight.

Termites are pushovers too. Like many social insects, worker termites spend a lot of their time carrying their larvae around. It makes sense: the larvae move slowly, so it takes them a long time to reach their food.

The newly discovered scarab beetle, Eocorythoderus incredibilis, has found a way to exploit the termites' helpful attitude. Not content with living in the termites' nest and stealing their food, it has persuaded the termites to carry it around. It even has a nifty handle on its back so they can pick it up easily.

Uninvited guest

Munetoshi Maruyama of the Kyushu University Museum in Fukuoka, Japan, discovered E. incredibilis in Cambodia earlier this year. He was digging through the nests of Macrotermes gilvus termites containing underground "gardens", about the size of a fist, where the termites grow a fungus that they eat.

After dissecting more than 130 such gardens, Maruyama had found 10 scarab beetles, each about 3 millimetres long. He realised the beetles belonged to a group called the Corythoderini, all of which hang around termite nests.

A closer look at the new beetles revealed that they are wingless and their eyes have shrunk almost to nothing. That suggests that they must spend their entire lives within termite nests, as they would struggle to survive outside. Maruyama says they probably eat fungi from the termites' gardens.

In a sense the beetles are parasitising the nests, but Maruyama says they are so few in number that they probably do not cause significant harm – they are basically just sharing the space.

Blending in

It seems the beetles secrete chemicals that mimic those of the termites, allowing them to blend in. "They have many gland openings on their body surface, from which chemical substances will come out," he says.

Their disguise clearly isn't 100 per cent reliable, as most of the beetles Maruyama found were injured, with cuts on their legs. He suspects the termites sometimes realise that the beetles do not belong, and attack them.

But it clearly works quite well most of the time. Of the 10 beetles Maruyama found, two were being carried by worker termites. The beetle retracted all its legs as soon as it was touched, and then the termite gripped the handle on its back in its mouthparts.

The beetle benefits from being carried to nutritious fungi, but the handle may have evolved as a survival aid, Maruyama speculates. He says the termite nests are often attacked underground by driver ants, which have powerful shearing jaws and can decimate the termites.

When a nest comes under attack, the termites often evacuate, carrying their larvae away to a safe distance. Evolving a handle may have ensured that the beetles were also carried out of harm's way.

Journal reference: Zootaxa, vol 3555, p 83