A lot of times chigger bites will show up in the least desired spots, along the waist line or ankle line near the band of a sock. Chiggers tend to migrate along your body under loose fitting clothes, and when they hit barriers like tight fitting clothing they tend to stop and then inject their digestive enzymes into your skin which causes the irritation. A common myth is that chiggers can crawl under your skin and they certainly don't drink animal blood. Your skin cells contain fluid, and the digestive enzyme enables chiggers break the skin down to feed off of those fluids.
An important thing to look out for with chigger bites is getting an infection. You can use certain types of antibacterial creams to help prevent secondary infections from chigger bites.