Daphnia lumholtzi invaded North American lakes and reservoirs. It forms prominent spines, which are inducible by fish kairomones. We tested the two hypotheses that the long spines protect against vertebrate (fishes) and invertebrate (Chaoborus) predators. Our experiments revealed that adults with longer spines survived significantly better under fish predation and juveniles with longer spines were additionally better protected under Chaoborus predation. Our study is the first direct proof that long spines effectively protect against both predators. Our results support the idea that the anti-predator devices may represent an important functional mechanism for the invasion success of D. lumholtzi.