Larval mass and survival data for Meadow Brown butterflies (Maniola jurtina) originating from nine different source populations in the UK and reared under one of two host plant treatment groups (either control or drought stress) in an outdoor insectary at UKCEH under natural environmental conditions. Each individual larva was monitored at three growth check points throughout development: 49 days after hatching (pre-overwintering), 162 days after hatching (post overwintering during larval growth) and 309 days after hatching (late larval growth and pupation phase). Larval masses (mg) were recorded for all individuals that survived up to the second growth monitoring point and the number of larvae that survived until the third growth monitoring point were recorded.