One impact of climate change on herbivores is altered water availability in host plants. Tetranychid mites are major agricultural pests, and previous studies show that those feeding on water-stressed plants have higher fecundity and faster development, likely due to increased nutrient availability and/or reduced plant defences. Early nutritional conditions can shape behaviour, increasing activity under high-quality diets or boldness under malnutrition. Such behavioural shifts may affect dispersal and predator responses, potentially increasing crop colonisation, making it important to assess how water-stressed plants influence herbivorous mite behaviour. The effects on higher trophic levels, such as plant-inhabiting predatory mites (Phytoseiidae), should also be investigated. Better-nourished pest mites may serve as higher-quality prey, potentially altering predator life history and behaviour. In this study, we tested these hypotheses using a tri-trophic system involving the host plant Phaseolus vulgaris, the herbivore Tetranychus urticae, and the generalist predatory mite Typhlodromus (Anthoseius) recki. Plants were grown under two watering regimes: daily watering (n = 41) or minimal watering to maintain soil just above the wilting point (n = 43). Five female T. urticae were placed per plant in a closed arena for ~64 h to assess fecundity. Development was then monitored daily. Typhlodromus recki females were reared individually and fed T. urticae from stressed (n = 26) or non-stressed (n = 25) plants; fecundity was recorded after five days, and development monitored daily. For behavioural assays, all individuals were videotaped for 5 min. For T. urticae females (non-stressed: n = 35, stressed: n = 41), we measured their tendency to explore a novel environment and willingness to move onto a leaf disk previously visited by predators. Adult T. recki females (non-stressed: n = 11, stressed: n = 10) were tested for exploration, and responses to conspecifics were assessed by grouping four females (two per treatment) and recording activity, inter-individual distances, and encounters (n = 24) Tetranychus urticae laid more eggs and developed faster on water-stressed plants. However, its behaviour did not differ between the two-watering regime. For the predator T. recki, life-history traits did not differ between prey from non-stressed and water-stressed plants, but behaviour changed: females moved less when feeding on prey from water-stressed plants. These preliminary results suggest that biological control may be less effective on water-stressed plants, as predatory mites showed reduced mobility. In contrast, herbivores exhibited improved life-history performance, likely allowing higher population growth.