Auckland Island Cave Weta - Dendroplectron aucklandense
The Story: Although cave weta do not have wings they have managed to get around the world very well. Cave weta have successfully colonized many islands and their habit of climbing into holes in trees has presumably allowed them to stowaway on logs drifting in the ocean. Each island group around New Zealand has its own unique cave weta. Campbell Island hasNotoplectron cambellense, and the Snares and Bounty Island each have their own monotypic genera. The cave weta unique to the Auckland Islands (found on mice-free Rose, Ocean, Adams and Ewing Islands) isDendroplectron aucklandense.
Cave Weta on Rata tree. Photo: Kath Walker.
Little is known about cave weta biology. We know that little nymphs hatch from eggs and they look similar to the adults, although their spines and genitalia are not fully formed. They are all nocturnal and so during the day need to hide from predators (such as tomtits). Predators of cave weta on the Auckland Islands are likely to be the two common endemic ground birds, the Auckland Island snipe and the Auckland Island rail, as well as tomtits and to a much lesser extent, juvenile falcon. A few species of cave weta use caves to hide but most cave weta species live their whole lives without once entering a cave. Instead they hide in hollow tree trunks or crevices between rocks or cracks in bark. On the Auckland Islands the cave weta hide primarily under the bark and in holes in gnarly old southern rata trees. They will also use the food store sheds of ecologists as suitable day-time refuges where they gather in large numbers quietly waiting for the night. All cave weta have small mouth parts and seem to eat a wide range of foods although perhaps some species are specialists and we lack information to match species with diet. People have observed cave weta scavenging on dead sea birds, nibbling fungi fruiting bodies, eating pollen, sap, slug slime, fruit, leaves, and dead insects. On the Auckland Islands Dendroplectron aucklandense have few competitors and have been observed in many habitats. It is probable that they feed on a range of things from pollen to dead birds.
Different species of cave weta seem to have independently left New Zealand to form new populations on each subantartic island. The Auckland Island Cave Weta has arrived from the mainland sometime since the Auckland Islands formed by volcanic eruption over 10 million years ago. All the sub-antarctic species have evolved in isolation. Taxonomists have since named them. Aola Richards, a taxonomist, has described four of these monotypic genera, and because she could see no close relatives in New Zealand she created a new genus for each island species. In the case of the Snares Island cave weta, Insulanoplectron spinosum, we still haven't found a close New Zealand relative, but Notoplectron from Campbell Island is closely related to the Pharmacus species who live high on mountains in the South Island. We are still finding new cave weta species all over New Zealand, so perhaps we will find relatives of all the subantartic weta if we just keep looking. We are working on producing a phylogenetic tree for NZ cave weta but with 19 genera and more than 70 species it is taking a long time. We have learnt a good deal but we can't yet draw even a simple family tree.
Classification: Kingdom - Animalia. Phylum - Arthropoda. Class - Insecta. Order - Orthoptera. Family - Rhaphidophoridae. Genus -Dendroplectron. Species -aucklandense(Richards 1964)
The Scientists: Mary Morgan-Richards: Associate Professor. Massey University. Kath Walker: Scientist, Department of Conservation. Steven Trewick: Associate Professor in Ecology, Massey University.
Mary is a biologist who works at Massey University. She teaches evolution and population genetics. Mary started studying weta when she was an honours student, inspired by looking at grasshopper chromosomes with Graham Webb in Australia and weta taxonomy from George Gibbs at Victoria University of Wellington. So for years Mary has been excited by weta mating systems, weta chromosome evolution, weta competition, and weta hybrid zones. "The more we find out about weta the more we know we have still to learn. I'm looking forward to the next 20 years of uncovering details of the secret life of weta."