If using fresh blueberries, wash and pick out any unwanted berries and debris.
Cut, pierce or "check" blueberries by placing in a mesh strainer and dipping in boiling water for 30 seconds and then shocking them in cold water to stop them from cooking further. This opens up the skin to allow moisture to escape from the inside.
Place pierced or checked blueberries on mesh trays leaving a little space between each berry. Put in dehydrator and dry at 135°F (57°C) for 8 to 18 hours. Time will vary with each dehydrator, size of berries and with temperature and humidity levels in your house. (My house in the middle of winter on the Canadian prairies is extremely dry and foods dehydrate very quickly).
Rotate trays and check blueberries at 6 hours to get a sense of how quickly they are drying.
Finished blueberries will be pliable and leathery with no signs of moisture when squished or cut open. Natural sugar in the blueberries may make them a little sticky. It can be tricky to distinguish between wet and sticky but you'll get the feel of it. If you have any doubt, dry the berries longer or let them cool a little. As they cool they will become firmer. Let rest on tray until cooled, at least 2 hours.
Once cooled totally and completely, place in an airtight container (glass jar is best). To condition the blueberries and ensure they are absolutely dry throughout, watch and shake jar for next 7 days. If the blueberries soften greatly, clump together or if there is any sign of moisture on sides of jar - return to dehydrator. If all is good, store in a cool, dark place for a year or more.