...The bush cricket!
Well done son, bollocks that account for 14% of your total body mass. If a human had balls of those proportions they'd be the weight of six bags of sugar, each.
Apparently this discovery has thrown accepted wisdom on the purpose of having big swinging sacks into doubt.
Take Chimps - female chimps sleep around with all the males in a group, and so the males have evolved massive balls so that each ejaculate has more sperm and competes, within the females uterus, against all the other males' sperm.
Now take Gorrilas - single males have exclusive access to loads of females, and have little pebbly bollocks. I wouldn't say that to their face mind.
With the bush cricket, however, it looks as if the reason they have big balls is so they can shag loads of birds in quick succession. ie they don't blow their whole load at once.
My girlfriend just sent me this link. Dunno what she's doing googling "massive balls" but there you go.