It could be pyemotes itch mites or straw itch mites. They feed on the insects that are typically in stored grains, wheat straw, and hay. These mites are frequently a problem for people doing landscaping or feeding horses and other livestock. People who handle mite-infested materials will be attacked.
If it is this pest, the best control strategy is to eliminate the mite's host insects. If possible, clean storage areas thoroughly and treat with a pesticide. As with all pesticides, follow the application and storage instructions on the label as required by law. If the bites on your arms and chest continue irritating you, please see your physician.
