Wednesday, August 4, 2010

A Dung Beetle (Rainbow Scarab)

I pulled into the DNR parking lot along County Road M just outside of Durand around noon today.   I wanted to get a closer look at the butterflies I spotted at the edge of the prairie.  A Red Admiral, Clouded Sulphurs and a Gray Comma.

Hackberry Emperor on dung
I spotted another dark butterfly near the north edge of the parking lot.  I got out of the Prius to take a closer look.  It was a fresh new Hackberry Emperor. I haven't seen any Emperors in several weeks, so I was surprised to spot this one sitting on what looked like a pile of raccoon scat (full of undigested field corn and red berries).

As I took the photo, a clump of scat started to move.  

At first I thought it was one of those "candid camera" tricks.  You know - there's an invisible string. Someone starts to pull on it.  It's supposed to startle me.

It worked.  I was startled.  But I was also curious.  There's no string, so what's making the dung move?

Rainbow Scarab Beetle pushing dung

I stood still and watched as a relatively large iridescent green, red and blue beetle with yellow antennae appeared out from under the clump of dung.  The first thought that popped into my mind was:  dung beetle!

In all the years I've walked in the woods, I'd never seen one before.  When I got back home, I did a search and discovered it's a Phanaeus vindex - a Rainbow Scarab Beetle.  The males of this species have a big black horn.  This one was hornless - a female, apparently working alone.

These harmless beetles usually work in pairs.  The male and female excavate holes under the dung pile and push the dung into them.  The female then lays her eggs in the excrement which provides nourishment for her offspring.

I was awed by the Herculean effort she put in to moving that dung.

She had to move it because the inconsiderate raccoon left it on top of the tightly compacted 
parking lot.  There's no way she could dig down under it.  Her only recourse was to push that dung over to the prairie on the south side of the parking lot.  

It took her 30 minutes to get the job done.


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