Spider movements aided by flight

The web of joy radiating from arachnologist James Crofts-Bennett when he talks about spiders is so strong it is almost visible.

The University of Otago PhD  student is helping catalogue the Forster spider collection housed at Tuhura Otago Museum.

Established by husband and wife arachnologists Raymond and Lyn Forster, the collection is the largest in the country.

"It is an absolutely mammoth collection," Mr Crofts-Bennett said.

"I believe it is 14,000 vials full of spiders."

Mr Crofts-Bennett is working on a digitised catalogue, recording the species, where it was collected and what year. 

He is also retracing the steps of the Forsters, revisiting locations in Otago where spiders were collected to see what changes have taken place over time and how it might have affected spider populations.

"The more and more I get into this, the more I realise that spiders are not static."

"So now I’m trying to look at perhaps not so much individual spiders in individual areas, but spiders as a whole in an area as the land changes."

One piece of research is helping understand spider movements.

It was thought spiders could "fly" by releasing a little bit of silk, and the wind picked them up and they "ballooned away".

But in 2019 physicists finally confirmed spiders fly using static electricity.

"Plants have roots in the ground, and they are drawing in water, but they are also drawing in salt, which is an electrolyte.

"As they are drawing in salt and other minerals into their body it creates an electrical gradient."

That means a positive electrical charge is generated at the top of plants.

Spiders can detect this electrical charge using very fine hairs on their body called trichobothria. 

They can then build up their own electrical charge, expelling it through their feet.

Spiders can match polarity with the plants’ electrical field and use that to propel themselves through the air, like magnets repelling each other.

 

SPIDERS ABOUND IN AUSTRALIA AND NEW ZEALAND

Arachnologist James Crofts-Bennett says globally about 50,000 different species of spiders have been named.

It is estimated another 40,000 species were still to be classified.

Australia and New Zealand could have about 12,000 different species, or 13% of the global spider population.

New Zealand has an estimated 2000 different species.

"So we are really are in a private little Eden for spiders, which makes me very happy."

The ecology of spiders is not that well understood.

"Their anatomy is quite counterintuitive.

"They have still got remnants of being a marine species, like they have book gills for their respiratory system."

This makes them vulnerable to desiccation.

simon.henderson@thestar.co.nz