Sheargrubs are enemies in both Pikmin games. They burrow underground, and when you approach, they dig out of the ground's crust. The Sheargrub species come in two colors, pink and purple. Pink Sheargrubs are female, and they don't do much anything when they come out of the ground. It is stated that they feed on dead Pikmin remains, but they can't harm your Pikmin. Purple Sheargrubs are male, and they have larger mandibles, allowing them to eat your Pikmin whole. This creature isn't dangerous though, you should easily be able to kill this creature and save your Pikmin by swarming it.
These creatures are also related to the Shearwig.