This insect resembles the common tomato bug in North America.
Half inch long
Specimen kindly supplied by Scott Loarie:
At first hopelessly clenched into a a tiny ball, now definitely dead but more relaxed.
Mixed emotions about this - I briefly thought I had discovered some crazy new woodlouse (my favorite group) but turns out it something called a California Pill Millipede, the only member of the family in Western North America and apparently restricted to coastal central CA. They can roll up into a ball and look ridiculously alot like woodlice. I only got these bad photos before he rolled up to a ball and refused to unroll, grrr.
Pill millipedes make up two orders of millipedes, often grouped together into a single superorder, Oniscomorpha. The name Oniscomorpha refers to the resemblance of pill millipedes to certain woodlice, namely the pillbugs of the family Armadillidiidae, also called "potato bugs", or "roly-polies".