Thanks to everyone who helped us with the compost grub mystery. It turns out they are larval green fruit beetles. I have seen the beetles around the yard before and wondered if they were friend or foe. It turns out they are pretty much neutral. They eat fruit but can’t do much harm unless the fruit is overripe or bird damaged. I’ll let the grubs stay and break down the compost although I think the raccoons or, more likely, skunks are rooting through our pile looking for them.

Ramshackle reader Josh says that his ducks and chickens love to eat them. He sent us this link to the Natural History Museum’s entomology research page on the Green Fruit Beetle. Thanks Josh!

Ramshackle reader katastrophik pointed us to whatsthatbug.com where the bug guy (Daniel) dropped this knowledge:

Hi Eric,

Congratulations. You have Crawly-Backs. Charles Hogue indicates in
his wonderful book, Insects of the Los Angeles Basin, that the grubs
of the Green Fruit Beetle or Figeater, are called Crawly-Backs. He
writes: “The adults are active from late summer to early fall and,
during this period, lay their eggs in compost piles and other
accumulations of decomposing plant litter. The larvae are fairly
large (2 in., or 50 mm, long) and C-shaped; the body is pale
translucent white, and the head is dark brown. The first two molts
are completed in the fall, the third the following spring. Larvae
move forward on their backs with an undulating motion of the entire
body. They obtain purchase on the substratum with transverse rows of
stiff short stout bristles on the back of the thorax. Because of the
peculiar manner of locomotion, they are known as ‘crawly-backs.'” The
adults are beautiful metallic green beetles that have a loud buzzing
flight.

Have your own bug identification question? You may want to ask the bug guy.

And, of course, once you know what you are looking for, there is always wikipedia.