What on Earth could this be?

Question

I've just gotten in from a walk, on which I found a very interesting but unidentifiable beetle.

It was about three-quarters of the size of my thumb, teardrop shaped (small head and wide butt) and had six legs, and a very hard, shiny shell on the back. It was greenish-yellow, but was particularly shiny right at the butt and the thorax. The shell presumably opened up when the beetle flew, but I just saw it drop out of a tree and crawl on the sidewalk. Its underside was a sort of greyish-brown color.

Like I said, the beetle dropped onto the sidewalk (presumably from the tree above) when I walked by. It crawled to a sandy area where some ants had built a hill, and then it dug for a while. I thought perhaps it would dig under the sand completely, but it just sort of got its belly in, then walked away after five minutes. It walked rather slowly for a bug, I thought, and didn't seem at all frightened of me even though it saw me.

I have never seen this sort of beetle before, nor have I seen

Answer 1

ive seen them before but i forget what they are called    dont eat them

Answer 2

Does it hum?  Maybe it's a humbug!

Answer 3

Only you saw it.  Research it in a Beetle Book Collection if you are that interested.  No help here

Answer 4

I think it's a type of stinkbug only one that is very hard to find.