The ability to grip unhatched eggs is a skill exploited by the ants Harpegnathos venator,as they care their brood in tunneled nests,which is of extreme difficulty to keep the eggs intact while gripping.In this paper we propose a mathematical modeling method to elucidate the mechanism of such a gripping behavior in the ant mandibles.The new method can be subdivided into following steps.As a preliminary,the concavity geometry and mandible kinematics are examined experimentally.Second,coordinate transformation is used to predict the real-time spatial topology of the concavity.Third,we come up with a new method to quantify the workspace required to grip and the contact area between the concavity and ant egg.Our model indicates that the biaxial rotation fashion with specialized concavities can reduce workspace by 40％ and increase contact area by 53％ on average compared with the uniaxial rotation pattern,which augments success rate of gentle gripping.This methodology may have applications in evaluating mechanical performance in both natural and artificial grippers.