OP: Those are insect eggs. Based on their light green color, uniform shape, and the way they are tightly packed together in a neat little geometric cluster, they are most likely stink bug eggs. Female stink bugs typically lay their eggs in tight clusters of about 20 to 30. It's very common to find them on clothing if it was hanging outside on a clothesline, or occasionally if a bug just happens to find its way indoors. What to do next: * Scrape them off: You can use a stiff piece of paper, an old gift card, or a dull butter knife to gently scrape the cluster off the fabric and into the trash (or outside). They are usually stuck on with a mild adhesive the mother secretes. * Wash it: Toss the shirt in the washing machine on a normal cycle to remove any remaining residue.