Katipo face invaders from South Africa

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Native katipo spiders are coexisting happily with a South African species that has invaded their niche in coastal sand dunes - but the two species may yet come to blows, says a researcher.

The South African intruder, Steatoda capensis, has established itself throughout much of the country, not just in the coastal sand dunes that katipo occupy, and it was originally thought it might quickly displace the katipo.

The intruder has wider habitat tolerances and can reproduce throughout the year, while katipo reproduce mostly in summer.

But researcher Jess Costall, of Massey University, said that though Steatoda existed at high densities in many coastal sand dunes, "the two spider species seem to be able to co-exist".

The South African species is known as the "false katipo" while the real thing is a New Zealand native closely related to the Australian redback and black widow spiders. Its Maori name translates as night-stinger.

"It is quite common to find Steatoda and katipo living on the same piece of driftwood," Ms Costall said.

The most common type of sharing was to have a juvenile of each species living on the same piece of driftwood, though katipo tended to prefer smaller pieces.

But this might not continue if push came to shove in the competition for suitable websites.

"While at the moment the two species appear to be able to coexist, if Steatoda populations increase further - or available sand dune habitat shrinks in size - we may have a problem."

But the main threat to katipo seemed to be humans, with some katipo populations along the Manawatu-Wanganui coastline appearing to be at risk of extinction at sites in Wanganui South and Castlecliff.

There was a need to reduce and reverse damage being done to sand dunes by vehicles, dumping, grazing by hares, and the spread of exotic plants with dense growth.

New katipo might have to be moved into these areas to bolster the local populations, Ms Costall said in a paper published in the New Zealand Journal of Zoology.

On the beaches at Himatangi and Foxton, there were healthy populations of the native species, scientifically known as Lactrodectus katipo, but the density of the South African spiders was twice as heavy as the katipo at Himatangi.

- NZPA