Exotic flying spiders dominate land after fires

Picture: Spider.jpg; A native trapdoor spider hangs on in a burnt environment. Research indicates introduced species have the advantage over native species when repopulating these areas.

Media Release

27 November

-for immediate release

Exotic flying spiders dominate land after fires

There may be another reason to be careful during the heightened fire risk of a dry summer in addition to the danger posed to people and property — big foreign flying spiders.

A Lincoln University and AgResearch study has found exotic spiders seem to be better at resettling burnt land than their eight legged Kiwi counterparts, dominating the area, depriving them of food, and altering the native ecosystem.

But it may not only be fire which could lead to an introduced airborne arachnid invasion.

Lincoln University Senior Lecturer Dr Adrian Paterson was one of the authors of a paper drawn from the four-year study on the subject of how tussock grassland was repopulated after a fire, using controlled burning of plots to gauge recovery.

He said in many spider species the young spiderlings use a line of silk they produce themselves, usually to make webs, to lift off the ground in a process known as ballooning. The wind does the rest.

The study found introduced species were better at ballooning than the native spiders and often larger as well, so they could walk over the burnt ground more easily – this combination meant they were quicker to repopulate a burnt area.

‘’More worryingly, any crisis that impacts on an area — say landslides, floods, human modifications — will result in the same benefits for these ballooning, large, exotic spiders, ’’ Dr Paterson said.

Findings suggested frequent fires could cause long lasting damage to the native spider fauna of tussock grasslands

The majority of New Zealand grasslands and mixtures of grass and shrubs have been modified for use as livestock pasture, often through burning, he added.

Dr Paterson said this provided exotic species with a way into these areas to colonise and then dominate, reducing the local native diversity.

In the study area most native species were still absent four years after the burning.

He said as far as the authors were aware, this was the first study which showed an increase in the abundance of exotic spider species after burning.

In New Zealand burning of native tussock grasslands is partly supported for preserving native vegetation by keeping exotic shrubs and herbs in check, he said.

This highlighted a potential conservation issue around the balance needed to maintain the diversity of native species, as the burning benefited the plants but was detrimental to the spiders.

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