Most insects fly—but, across millennia, many species have lost the ability. Island dwelling insects have been especially prone to this evolutionary trend. In fact, on the small islands clustered between Antarctica and Australia, almost all insects have lost the power of flight. In this so-called sub-Antarctic zone, on islands such as Heard Island and Campbell Island, flies creep and moths crawl.
Charles Darwin knew about this wing loss habit in island insects from a book he read about insects on Madeira Island. Over 160 years later, his simple explanation of this phenomenon remains the most plausible, according to biologists. Darwin’s position was essentially this: If an insect flies, it’s more likely to get blown out to sea. This is especially true of the Sub-Antarctic Islands, which lie in the path of strong westerly winds that blow through the Southern hemisphere—winds with nicknames such as “the roaring forties” and “the furious fifties.”
These islands are some of the windiest places on earth—making it difficult and taxing for insects to fly there. Those insects left on land to produce the next generation are those who are most reluctant to take wing. Insects that stop investing in flight and structures such as wings and wing muscles redirect their energy and resources towards reproduction. Over time, these species lose the practice of flying—and then the equipment, too.
Eventually, evolution ensures the survival of island insects that do more running and less gliding. Though, of course, there are other dangers on these islands, and a bug ambling over the rocks is never far from any of them.