I discovered this beautiful creature on a piece of straw in our garlic bed.
A visit to the ever-helpful Garden Insects of North America identified it as the larva of a variegated fritillary (euptoieta claudia).
Evidently these are commonly known as pansyworms, due to their appetite for pansies.
The book says they can be damaging to gardens, but I saw no damage to any garlic so I left this one in peace.
The caterpillar has this destiny.