Like virtually all geologically young, small oceanic islands and archipelagos of volcanic origin, the Galapagos should not have certain groups of organisms. Neither amphibians, for example, nor freshwater crabs are found in such places. This is because these freshwater-dependent organisms are extremely unlikely to survive an oceanic voyage needed to colonize remote islands, and even if they somehow make it across, the chances of finding an appropriate aquatic habitat on the island are virtually null. I was therefore quite surprised, nay, shocked, when I spotted on a trunk of a tree in the middle of Santa Cruz island a small velvet worm. Then another one, then another, and two more, and fifteen additional ones. The place was crawling with them.
How could that be? Let’s begin with the fact that velvet worms, members of the somewhat enigmatic phylum Onychophora, are notoriously difficult to find. In my 20+ years of working in the tropical areas of the world I can count on the fingers of one hand all the velvet worms I have ever seen. These animals are also tied to highly humid habitats, and apparently (although I could not verify this information) they will die if the air humidity around them drops below 80% – these are seriously humid conditions. Clearly, an animal like this is very unlikely to be able to colonize remote volcanic islands. And yet, there they were, and plenty of them.
As you might suspect, they are a very recent arrival to the Galapagos. They were first spotted in 1992, most likely brought inadvertently with a shipment of bananas from South America. From the shipping docks of Puerto Ayora they have spread to higher, more humid areas of Santa Cruz, and flourished ever since. Their high abundance can be explained by the fact that the Galapagos lack most of their natural enemies; centipedes in particular, their main predators in places where velvet worms naturally occur, are rare in the archipelago. Velvet worms are themselves hunters of small invertebrates, and where I found them, in a humid forest of Santa Cruz, schizomids (tiny arachnids, also introduced) and small isopod crustaceans were plentiful. Based on the photos I took I was able to place the Galapagos velvet worms in the genus Oroperipatus of the family Peripatidae, which indicates that they must have arrived from somewhere in South America north of Chile (which has members of a different velvet worm family, the Gondwanan Peripatopsidae.) It will be interesting to see if they manage to colonize other islands of the archipelago in the coming years.