Okay, first of all, I understand where that line of thinking comes from: “If there are 300 species of grasshoppers worldwide, why is this one so important?”

I’d answer on two levels, one local and one global:

1. Locally Wetas are special in that, since there have never been any mammals in their habitat other than seals and bats, they fill the ecological niche of small rodents such as mice. This means that, at the trophical level, they serve as the link between lower trophic levels and the predators at the top of the food chain. Since the entire ecosystem is endemic due to New Zealand’s isolated location and all species are specialized to coexist with one another, the disappearance of the weta could trigger a chain reaction leading to the extinction of a whole range of other species. This is because weta fill the niche that mice occupy elsewhere, but they are insects, not mammals (differences include metabolism, nutrient content, feeding habits, etc.).

2. Global We have enormous biodiversity globally. In an ecological context, diversity means resilience to disturbances. Let me explain with an example: Let’s assume that there are perhaps 500 tree species globally in the temperate zones. One might ask again: Why do we need 500 species when 10 would suffice (ideally fast-growing ones that are useful to us humans)? The difference lies in the resilience of our timber supply: If, in a system with 500 species, one, two, or even five species are damaged by a newly emerging pest, climate change, or some other factor, this accounts for about 1% of the total biomass. In a system with only 10 species, however, the same change would result in a loss of 50% of the biomass (and thus of the timber yield usable by us humans), not to mention the consequences for ecosystems… and there, too, we would be indirectly affected through ecosystem services such as water purification, etc. We as humanity therefore have a vested interest in preserving biodiversity. Not out of goodwill… but purely out of selfish self-interest and to protect ourselves from disruptions to our means of subsistence (which we are already severely undermining due to other issues).