I wish they would (go that is!)
I found loads of these in my garden yesterday and hadn't a clue what they were. It seems that they are Musk Beetles "Aromia Moschata". Thanks to Rob (notbob) for identifying it. Here's more information:
The xylophagous larvae (literally "mangeuses of wood") develop on the willows, more rarely in the poplars and the alders. Several years are passed until the nymphose. The adults suck the sap of the willows, maples and birches. The name of the species comes from secretion, with the back of the lower part of the thorax, of substances of bases are drawn from the feeder plant and undergo a chemical conversion in glands. Because of systematic demolition of the old willows, the species with tendency to rarefy.
That explains my dead willow tree!!!
NotBob
Pro 
That's no thunderbug.
Thunderbugs are much smaller.
http://en.wikipedia.org/wiki/Thunderbug
It looks more like a musk beetle //(Aromia moschata)//, a species of longhorn beetle belonging to the subfamily //Cerambycinae//, tribe //Callichromatini//.
Its name comes from the musky smell it emits.