I don't think it has anything to do with microbes. Starch is made from organic products -- usually corn, but it can also be made from rice and potatoes. This is "food" for certain bugs. Whether or not storage of fabric with starch in it attracts bugs seems to depend on where you live as well as on how the fabric is stored. A damp basement or a tropical, humid climate are likely to have bugs who like to eat starch. I've never had a problem, but we air-condition the house during the hot season and we don't have any dampness in the house.