Galloping beetles could be counting steps

Oct 21, 2013

(Phys.org) —A species of dung beetle in the Western Cape has given up its ability to fly and instead gallops across the sand in a behaviour which researchers suspect evolved as a way to navigate back and forth from home.

"This species of Pachysoma grabs bits of poo and gallops forward with it. That is really odd. Most insects walk with a tripod gait. They plant three in a triangle, while swinging the other three legs forward. It's an incredibly stable way of walking because you've always got three legs on the ground. For an insect to abandon the tripod gait and use its legs together in pairs like a galloping horse is really radical. The big question is: why are they doing it?" says Professor Marcus Byrne of Wits University.

Pachysoma is also different to most dung beetles in that it collects dry dung and hoards it in a nest which it provisions with repeated foraging trips, instead of rolling one, wet, dung ball in a straight line away from competitors at the dung pile, never to return.

A team of scientists including Byrne and colleagues from Lund University in Sweden think the species might have changed the way it walks because it needs to be able to find its way back and forth from its nest.

"For most dung beetles, it's always a one way trip – grab the poo, run away and never go back. The very marked pacing of Pachysoma's gallop might be giving it a better signal in terms of estimating the return distance from the food to its nest. When it gallops, it slips less in the soft ," says Byrne.

This video is not supported by your browser at this time.
Pachysoma Endrodyi Butterfly Gait.

Ants have been shown to count their steps as a way to navigate back and forth from home, and bees have been proven to use the optical flow of scenery across their retinas to measure how far they've travelled to forage from the hive. The team thinks the Pachysoma dung beetles are doing both.

"Bees use optic flow as a measure of how fast and how far they've flown. Dung beetles have two eyes on each side of their head, one on top and one on the bottom, looking at the sand and we think Pachysoma might be registering with its bottom eye over the sand," says Byrne.

But Pachysoma has not only changed the way it moves across land, it has also lost its ability to fly.

"There are 800 species of in South Africa and most of them fly. To fly makes sense because poo is a very ephemeral resource. It's only useful for a few days and it's very patchy – you don't know where you're going to find the next dropping. That's why Pachysoma is so weird. Why would anyone give up flying?" says Byrne.

The team suspects that Pachysoma has sealed its wing cases to conserve moisture in the arid West Coast environment. "Breathing causes massive water loss. We think they've closed the elytra case to create a breathing chamber which keeps moisture inside," says Byrne.

The unique behaviour of this galloping, flightless species has allowed it to dominate a niche market among dung collectors of the Western Cape.

Explore further: Study pumps up the volume on understanding of marine invertebrate hearing

Related Stories

Dung beetle dance provides crucial navigation cues

Jan 18, 2012

(PhysOrg.com) -- The dung beetle dance, performed as the dung beetle moves away from the dung pile with his precious dung ball, is a mechanism to maintain the desired straight-line departure from the pile, ...

Beetles use dung balls to stay cool

Oct 22, 2012

Dung beetles roll their feasts of dung away to avoid the hoards of other hungry competitors at the dung pile. But now a team of researchers from South Africa and Sweden have discovered that they also use ...

Dung beetles use stars for orientation

Jan 24, 2013

You might expect dung beetles to keep their "noses to the ground," but they are actually incredibly attuned to the sky. A report published online on January 24 in Current Biology shows that even on the da ...

Flapping protective wings increase lift

May 29, 2012

New research from Lund University in Sweden reveals the value of carrying two layers of wings around. The researchers studied dung beetles and the way their protective forewings actually function. These wings do not only ...

Exotic manure is sure to lure the dung connoisseur

Apr 11, 2012

Although the preference of dung beetles for specific types and conditions of dung has been given substantial attention, little has been done to investigate their preference for dung from exotic mammals found on game farms ...

Recommended for you

Ninety-eight new beetle species discovered in Indonesia

10 hours ago

Ninety-eight new species of the beetle genus Trigonopterus have been described from Java, Bali and other Indonesian islands. Museum scientists from Germany and their local counterparts used an innovative approa ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.