The Plainville Public Library is holding an online scavenger hunt this month to promote its “Dig into Reading’’ summer program. The reading program’s mascot, dubbed “DigDug,” was photographed at various locations throughout town; the photos were posted on the library’s website for residents to try to identify. The grand prize is four tickets to Southwick’s Zoo in Mendon, and a reusable tote bag. Two runners-up will win reusable tote bags filled with items to occupy children during car rides. Entry forms can be found at the library or online, and must be completed and submitted by July 29 at 8 p.m. For more information and to view the scavenger hunt photos, visit www.plainvillepubliclibrary.org .