I know is a terrible picture, but is this a harlequen bug? He and a 100 of his relatives are eating my cabbage. Eta:
its confirmed as Harlequen bug, thanks 
pyrophile.
Question, how do you control this pest.
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I have large quantities of brassica seedlings for the fall, and I didn’t want any of these bugs to live. So I havested all of the mature cabbage for saurkraut. I placed the roots, outside leaves and any damaged cabbage in a large barrel of water and crushed the bugs by hand as the swam to the top. Other than cabbage worms, which are so numerous I had to resort to Bacillus thuringiensis. I hope that makes my fall crop safe.
