Alpine scree weta

New Zealand is a unique and beautiful country that evolved for millions of years without the presence of terrestrial mammals meaning. Because of this many of New Zealand’s species had to evolve to fill the niches that mammals would normally fill causing NZ to have some unusual and wonderful fauna including the weta which is a member of the Orthopteran order. Weta are an iconic insect that has the unique role off being a seed disperser for plants with fleshy fruits; a role that is usually carried out by mammals or birds. The more commonly known seed dispersers are ants but unlike ants weta disperse the seeds after consuming the fruit so the seeds travel through the gut passage.

The alpine scree weta (Deinacrida connectens) has a mutualistic relationship with fruit bearing plants including the mountain snowberry plant (Gaultheria depressa) where the weta, in exchange for food (the plant’s fruit), will disperse its seeds. Of course since there is no such thing as true mutualism; many of the plants seeds are predated on especially by smaller weta.  

This mutualistic relationship was investigated in the paper Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta (Deinacrida connectens) where snowberry seeds were fed to weta in cheese to see how many would pass through the gut passage intact. The weta were of varying sizes and it was found that the larger the weta the more seeds consumed and dispersed whereas the smaller weta acted more as seed predators and dispersed only a small number of seeds. Also the larger weta were able to disperse the seeds over greater distances meaning that the seeds can be further from the parent plant and are unlikely to compete with it for resources.

Since this investigation was carried out under lab conditions the results may not reflect what actually happens but many seeds were recovered from the captured weta before the actual investigation began. This shows that the weta do have a role in seed dispersal but the extent of that role in the wild hasn’t been studied.

A similar investigation was done with Wellington tree weta (Hemidenina crassidens) and tree fuchsia (Fuchsia excorticata) which came to the same conclusion as the other investigation that weta can be important seed dispersers in New Zealand and that the larger the weta the more seeds they can disperse over longer distances.