White grubs are identified by the shape of the vent, or anal slit, and the pattern of a series of spines that site in front of the vent. These combined features make up a grub's raster pattern.
Japanese beetle grubs have a horizontal vent and spines that form a V-shape. Oriental beetle grubs, common in coastal areas, also have a horizontal vent. However, the spines of the Oriental beetle form parallel rows. European chafer grubs have a Y-shaped vent and two long, parallel lines of spines. The vent of the Asiatic garden beetle is branching, and there its spines form a semicircle. June beetle grubs are among the easiest to identify because of their tendency to use a series of ridges on their back for locomotion, while their belly and characteristically small legs face upward.
Examining the raster pattern of a grub requires a steady hand, patience and a good magnifying lens. Grubs should be held with forceps or between the index finger and thumb and a small tool used to uncurl them from their defensive posture to get a good view of the tail end. Identifying grubs is important for management and damage control because different species behave differently and require different mitigation techniques.