Spider mites are tiny plant-feeding animals that cause major damage in agriculture. Unlike most other pests, spider mites can feed on an extraordinary range of different plants. This is remarkable since these plants often produce many different toxic compounds as a defense against plant feeding animals. Recently it was found that mites may use simple tricks to cope with the defenses of plants: rather than trying to detoxify all those different toxic substances, they force plants to stop the production of some defensive toxins. We think that specialized substances in their saliva are injected into the plant while feeding. These secreted substances that hijack the plant’s defensive metabolism are called effectors, and have only rarely been found in herbivores. We recently identified a novel group of candidate effectors from spider mites. Here, taking advantage of several new resources and techniques, we propose to study these effectors in detail: how many are secreted and how do they work? We want to investigate which plant processes are affected by these effectors, in order to identify plant genes that are targeted by the mites to switch off defenses. This knowledge can then be used to breed plants that cannot be manipulated by spider mites any longer. In doing so, we aim to protect crops in an environmental friendly and sustainable manner.