Dragonflies arrive across open ocean, where no larva could have lived

Globe skimmers turn up on islands and ships hundreds of kilometres from the nearest fresh water. Their young can develop only in fresh water. The adults crossed.

Pantala flavescens breeds in temporary pools. The larva cannot survive the ocean. Yet the adults appear on the Maldives, on ships in the Indian Ocean, and on islands with no permanent freshwater, in numbers, and in season with the winds that blow off India and, farther along, toward East Africa. Charles Anderson set the arrivals against the meteorology in 2009: the insects are not breeding where they are found, and the wind at altitude is a conveyor going the right way at the right time. Later isotope work on their wings has pointed the same direction. A transoceanic circuit, possibly multi-generational, is the reading that fits.

What has not been done is to put a transmitter on one dragonfly in India and download it in Tanzania. They are too light. The evidence is presence where a life cycle is impossible, plus the wind. That is weaker than a tern’s logger and much stronger than a sailor’s yarn, because the sailors’ yarns now have dates, counts, and a map of the monsoon. An insect with a brain the size of a seed is crossing hundreds of kilometres of sea. Some of the proposed route is thousands.