I studied biology at the University of Leiden, where I obtained the equivalent of a M.Sc. in 1974, specialized in Animal Ecology, Plant Sociology and Management of Nature. In August 1974 I was appointed as assistant at the division of Animal Ecology and started to work on the ecology of parasitoids. I did my PhD in 1982 with a thesis titled “The foraging behaviour of the Asobara tabida, a parasitoid of frugivorous Drosophila species”.
In 1984 I became Associate Professor. Since 1990 I was the head of the section Animal Ecology, and since 1999 Professor of Animal Ecology at the Institute of Biology of Leiden University. From 2006 to 2009 I held a Marie Curie Excellence Chair at the University of Rennes 1, France.