Investigating momentum transfer with gall-forming wasps

Neuroterus saltatorius is a gall-forming wasp species endemic to the U.S. During summer, large numbers of galls detach from oak leaves and fall to the ground. They jump several times per minute in random directions earning them the moniker "jumping galls" or “flea seeds”. The mechanism behind this unique behavior has not been established, but one hypothesis suggests that encapsulated gall larva forces fluid through its U-shaped body at high speeds. The momentum of this fluid is transferred in such a way that a hopping motion occurs. We believe that understanding momentum transfer is important for applications focused on momentum transfer. Inspired by the jumping gall and to understand momentum transfer, we constructed a model using a mousetrap with attachable weights to demonstrate that a moving mass can cause jumping through momentum transfer. We predicted that adding weight to the arm would increase the jump height because the arm swings at the same speed with increased momentum from the larger mass. Increasing weights to the arm allowed us to identify the optimal mass for the highest jump. This modeling approach provided insights into the physical process underlying the galls' jumping behavior and extended beyond that. An application of the theory is to use momentum transfer when exploring microgravity environments like comets and asteroids because instrument packages cannot be moved by wheeled vehicles on extremely rough surfaces. An alternative is to construct robots capable of moving by momentum transfer.