Last week the question was: What kind of caterpillars are these on this broccoli leaf? (Hint: They hatched from eggs that were laid in a cluster rather than singly.)
These are early instar cross-striped cabbageworms. Their eggs are deposited in clusters of 20-30 as opposed to most other brassica eating caterpillars which deposit their eggs one at a time. Cross-striped cabbageworms can devastate a crop quickly because of their numbers. Here is a broccoli leaf that has been destroyed by these guys.
Here is this weeks question: What is this weed?