A Blackberry has a white fleshy core that will stay within the berry when you pick them and overall larger cells than a raspberry. Although blackberries are more tart than a raspberry they are an added treat to any desert recipe!
In a raspberry, red or black, they are hollow in the center when they are ripe. Raspberries are also smaller, and covered with tiny hairs (although both can have some hair attached). These little fruits are also harvested earlier than blackberries; ranging from June to August but can tolerate a little cold if the weather changes quickly.
Get out there and pick as many as you can of either kind!