On 11 February 2014, dozens of Portuguese man-of-war specimens were washed ashore along the entire stretch of Patos Beach (northwestern Spain). Here we performed both field experiments and numerical simulations to estimate the possible trajectories and region of origin of this swarm. On the one hand, our field experiments confirm the need to consider the main characteristics of an organism when predicting its drift. On the other hand, the numerical simulations show that this swarm originated in the open North Atlantic Ocean. The drift of the swarm was controlled by the succession of storms that hit the coasts of Western Europe in the winter of 2013 -14. Our findings also suggest that most of the individuals of the swarm were right-handed.