Hybridisation of different species or isolated populations is an important driver of animal speciation. Hybrid populations oftentimes outperform their parent populations due to novel genetic combinations, exhibiting hybrid vigour. Conversely, hybridisation can also lead to worse performance due to outbreeding depression. The wasp spider Argiope bruennichi has undergone a hybridisation event with Mediterranean and Asian populations mixing and resulting in a genetically distinct Northern European population. With this study we tested if hybrid offspring could outperform their parent populations under novel, disadvantageous conditions, namely climate and food availability. We found that spiders with a Mediterranean mother and an Asian father had very low hatching rates and high mortality and slow growth compared to the pure lines, and spiders with Asian mothers and Mediterranean fathers performed comparably to their parent populations. These results suggest mitonuclear incompatibility of the first combination and an increased role of the second in the stabilization process of a hybridising population. Additionally, we observed extreme developmental plasticity as a reaction to climatic cues in all backgrounds, which likely aided in the rapid historic poleward range expansion of this species.