Farming spiders: Finding arachnids in pasture

We construct much of our lives around events. If you asked me what had happened in my life over the last year I would give you some highlights: eldest son getting engaged, middle son moving to Auckland, youngest son finishing his degree, seeing Bill Bailey live, a nice holiday in Arrowtown, a walk around the tree-tops in Hokitika, watching the Black Caps get to the world cup 20-20 cricket final. Maybe also some lowlights: my father’s death from cancer, a covid lockdown, dealing with the Ministry of Education (in my role as a board member for our local high school), the Black Caps losing the world cup 20-20 cricket final.

The Westcoast Treetop Walk is something to remember! Image from Adrian Paterson.

While this is a good overview of the year it actually misses the things that I did for most of the time. It misses the 300+ hours of many days spent preparing the local cricket wicket (and the 100 hours of coaching), or the 41 books that I read, the 12 movies I went to, the 89 board games that I played, the 132 hours of lectures that were taught, the thousand meals that I ate, the sleep that was slept, the lawns that were mowed, the washing that was hung out and so on. The commonplace becomes invisible or at least fades into the background. And yet these behaviours dominate our lives.

Science can be a bit like this as well, especially in ecology. Working on kiwi or kea is exciting (and necessary). But what about the species we see the most? Blackbirds are everywhere, even your own garden, but they are reasonably invisible to research (despite also be necessary). If you look in museum collections of bird skins in New Zealand you will find far more tui then sparrows, despite sparrows being found everywhere. Habitats are the same. Working on kiwi in the bush of Fiordland or kea in the alpine zones of the Southern Alps is so much more memorable than starlings in urban central Christchurch or thrushes on the farms of Mid-Canterbury.

Movies I went to over last year (I know – but I am a scientist and like collecting data!). Image from Adrian Paterson.

We do need to know what is happening in these less than exciting habitats. About a quarter of New Zealand is in pasture. That is a huge habitat and there is little research on its contribution to biodiversity values. For an ecologist, pasture may not be the type of habitat that you saw in Attenborough documentaries as a kid, or that inspired you into the field. However, they are a crucial part of the landscape and we need to know a whole lot more about them. We need to make them visible.

Kate Curtis is keen on spiders. She is training to be a spider taxonomist, identifying which spiders are found in New Zealand and finding and naming new species. There are about 2000 native spider species in New Zealand. Most live in native habitats and we really only know something about half of these. We know sod all (a scientific term) about anthropogenic (human-altered) landscapes, like pasture. Do they mainly contain introduced spiders that are used to living in these habitats? Are there native species that are making the most of this space? Do different types of farming change the species that live in these pastures?

Spiders are top predators in their systems and often indicate if there are challenges occurring to other types of animal and plant species living in these systems. Establishing spiders diversity is a lot like taking the temperature of a patient. To be useful, you need to be able to take a temperature of a patient with the same tool as you would other patients so that you can easily compare between them.

As part of her Master of Science, Kate set about developing a protocol for recording the spider species that are present throughout New Zealand pastures. She wanted to create a best practice that could be passed on to anyone who wants to find out about spider diversity in their paddocks (and perhaps assess the health of their farms).

The native species Taphiassa punctata. Found only in pitfall trap samples (as was the introduced Steatoda capensis above). Images from Kate Curtis.

Kate was keen to develop a COBRA (Conservation Oriented Biodiversity Rapid Assessment) protocol. This is an initiative to create a system that could be compared to other habitats both in New Zealand and overseas. The idea behind COBRA is to first sample diversity very intensively, using different methods and then figure out the minimum amount and type of sampling effort, in the minimum time, that would give you approximately the right answer.

Kate sampled at three different Lincoln University farms. At ten sites on each farm Kate set up different collecting methods: ground searching (literally Kate hunting spiders along a transect), sweeping (using a net to sweep along the grass), suction sampling (a vacuum device that picks up most insects from a small area) and pitfall traps (small containers placed in pits whose tops are parallel with the ground into which spiders can fall). 

In a paper published in the New Zealand Journal of Zoology, Kate reported that she found spiders from 28 different species in the pastures. Pitfall traps recovered 27 of the species, ground searching 21. All 21 were also found in the pitfalls. Suction sampling recovered 6 species and sweeping 2. One of these species, Novakiella trituberculosa, was only found by suction and sweeping.

The introduced Drysdera crocata was found in both pitfall traps and ground sampling. Image from Kate Curtis

Based on this data Kate was able to estimate collecting curves. For example, if you collect from 100 sites and find 26 species but you can collect from 60 sites and still find 25 species then you can scale back the amount of sites as you are getting diminishing returns for all of your work.

From this data Kate was able to devise a COBRA protocol for pastures in New Zealand. There should be 12 samples with 4 pitfall traps for each sample, totaling 48 pitfall traps. Ground sampling is best carried out between 11pm and 1 am and six hours of search effort should be done. Suction sampling is an optional extra, it won’t find many species but it may get a species or two that will not be collected by the other methods.

Hopefully, with this work, Kate will encourage others to look at the diversity of pastures and allow some light to shine on one of the more common, if reasonably invisible, habitats.

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