Blue Jays eat fruit, nuts, berries, seeds, and suet. At the feeder their first choice would be peanuts in the shell. In the wild, blue jays eat lots of different foods. Though they are primarily vegetarian they also will eat caterpillars, beetles and other small bugs. Rarely do they eat eggs and nestlings.
To prepare for harsh winter weather they will collect acorns and other tree nuts and cache or hide them up to 2.5 miles from their original source and retrieve them when needed.
This behavior of burying seeds has greatly helped with the range expansion of many oak species. The rapid northward dispersal of oaks after the ice age may have resulted from the northern transport of acorns by Jays.
In one research study, 50 Blue Jays were observed selecting and caching 150,000 acorns over a period of 28 days. Each bird cached a total of 3,000 acorns by selecting and hiding an average of 107 acorns per day.