Daily Bucket - Dung Beetles @Night

The Daily Bucket is a place where we post and exchange our observations about what is happening in the natural world in our neighborhood. Each note about the bugs, buds, and birds around us is a record that we can refer to in the future as we try to understand the patterns of nature that are quietly unwinding around us.

Remember the recent Daily Bucket about the dung beetle? It showed that African dung beetles (Scarabaeus satyrus) use strong light cues from the sun and moon to navigate. There is more to the story.

“Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths,” Marie Dacke, of Lund University in Sweden, said in a prepared statement.

“We were sitting out in Vryburg [in South Africa] and the Milky Way was this massive light source,” said Marcus Byrne, of Wits University and co-author on the new study, in a prepared statement. “We thought, they have to be able to use this—they just have to!”

Their findings were published online January 24 in Current Biology.

To see if the starry sky was their guide, researchers set up some ingenious tests for the industrious creatures. Join me below the orange dung ball trail. Clearly, this fellow had no idea where it was going.

Researchers designed special cardboard and clear caps. The cardboard cap kept them from seeing the sky. On a starry, moonless evening, they started the dung beetles with cardboard caps from the center of a ring. The area was flat and sandy, surrounded by a wall. Beetles in a second group were uncapped. A third group wore clear caps. Beetles with no caps and those with clear caps had normal 'straight' paths. Beetles with cardboard caps took longer and had more erratic paths. Apparently they were seeing something in the night sky.

The researchers made a second ring to make sure nothing like trees or bushes were visible to the beetles. The beetles were timed to see how long it took them to reach the outer edge after starting from the center. Straight paths would reach the wall sooner. Wanderers would take longer.

Bright Moon In Sky	Average of 21 seconds
Starry Sky With No Moon	Average of 40 seconds
Cardboard Caps On Beetles	Average of 125 seconds
Overcast Sky Conditions	Average of 117 seconds

Were the beetles seeing the stars, or the Milky Way stripe across the sky? “The vast majority of these stars should be too dim for the tiny compound eyes of the beetle to discriminate,” the researchers noted in their paper. They took their beetles and rollerball arena to the Johannesburg Planetarium. It could project 4,000 stars and the Milky Way on the domed ceiling for the beetles to see. They tested them again.

Stars and Milky Way Showing	Average of 43 seconds
Only Milky Way Showing	Average of 53 seconds
Only 18 Bright Stars Showing	Average of 83 seconds

“This clearly shows that the beetles do not orientate to a single bright ‘lodestar,’ but rather to the band of light that represents the Milky Way,” the researchers noted. “This finding represents the first convincing demonstration for the use of the starry sky for orientation in insects and provides the first documented use of the Milky Way for orientation in the animal kingdom,” the researchers wrote.

What's going on in your backyard lately? Do you have signs of spring yet? Or, is winter still entrenched in your backyard? Tell us where and what is happening. It's good to have you stop by again.

Our group is blessed with more members than before. It is great to hear from people all over. Some regular diarists like to publish on the same day each week. Others publish when they have a diary ready on no particular schedule. We want to hear from them all. As we prepare to use the Publication Manager, take a look at the queue and the recent diary list for our group. Allow at least 2 or 3 hours between diaries so the authors enjoy the most interactions and commentary possible. We look forward to hearing from you.