A male western hercules beetle, Arizona.

Meet Dynastes granti. This behemouth of an insect is North America’s heaviest scarab beetle, found in the mountains of the American southwest where adults feed on the sap of ash trees. I photographed these spectacular insects a few years ago while living in Tucson.

The impressive pronotal horn on the beetle pictured above indicates a male; females are considerably more modest in their armaments:

Male and female hercules beetles

As is so often the case in animals, males use their horns to fight each other for access to females, attempting to pry their opponents off the branches.  Size is important, and it varies notably among individuals depending on how well they fed as developing larvae:

Size variation among male hercules beetles. My money is on the guy on the right.

The three beetles pictured here lived in our house for a while as pets; they were good-natured insects and would sit happily on our fingers eating maple syrup.

Photo details: Canon 100mm f2.8 macro lens on a Canon EOS 20D.
ISO 400, f3.0-f5.0, 1/50-1/125 sec, ambient light at dusk