Resource competition among herbivorous arthropods has long been viewed as u
nimportant because herbivore populations are controlled by predators. Altho
ugh recently resurrected as an organizing force in arthropod communities on
plants, there is still general agreement that resource competition among h
erbivores is reduced by predators. Here we show the reverse: predators indu
ce interspecific resource competition among herbivores. We found that thrip
s larvae (Frankliniella occidentalis) use the web produced and inhabited by
the spider mite Tetranychus urticae as a refuge from predation by the phyt
oseiid mite Neoseiulus curumeris. Thrips larvae prefer clean plant parts, b
ut move into the web upon perceiving volatile cues associated with thrips a
nd predators. This behaviour leads to lower predation risk, but also to red
uced developmental rate and lower production of thrips larvae due to compet
ition with spider mites. In addition, thrips larvae consume spider-mite egg
s. Thus, predators induce interspecific competition and intraguild predatio
n among herbivores within refuge space, even when host plants have an overa
ll green appearance.