 In order to find proof those individuals were migrants, we developed a technique to sequence the pollen grains that the butterflies were carrying in their bodies. Pollen? Pollen, yeah. So they just pick this up? Yes, when they visit flowers, they just get attached pollen grains from the flowers and this is how they pollinate other plants. And so the pollen is effectively the passport, is it? It told you where they'd been? Correct, yeah, that might be passport.