The other form of policing occurs through aggression towards egg-laying workers. In a species of tree wasp "Dolichovespula sylvestris", Wenseleers et al. found that a combination of aggressive behavior and destruction of worker-laid eggs kept the number of worker-laid eggs low. In fact, 91% of the worker-laid eggs were policed within one day. They also found that about 20% of workers laying eggs were prevented from doing so through both the queen's and workers' aggressive behavior. The workers and the queen would grab the egg-laying worker and try to sting her or push her off the cell. This usually results in the worker removing her abdomen and not depositing her eggs.