Chafer beetles’ overseas attack
They are the stuff of nightmares - the arachnid with a menacing red stripe and enough venom to kill a person.
The Australian redback spider has found the perfect home-awayfrom-home in an 81 hectare nature reserve in Cromwell, Central Otago.
University of Otago researcher Jackie Spencer says it’s perfect due to the hot, dry climate, an easy-to-catch food source and rabbits.
The reserve is also home to the critically endangered Cromwell chafer beetle, the only place in the world the beetle lives.
Now new research led by Spencer has confirmed redback spiders are using empty rabbit holes as an easy way to catch and devour the chafer beetle, threatening their existence.
‘‘We already knew that they were in the reserve. It was whether they were building their webs in old rabbit holes and whether the rabbits were aiding the redback spiders,’’ she says.
Spencer recorded and analysed prey caught in redback webs in the reserve over a four-month period and studied what impact filling in rabbit holes had on spider populations.
Her research found 99 per cent of redback spiders in the Cromwell Chafer Beetle Nature Reserve had built their webs in old burrows and the chafer beetle was the second-most common prey found (the most common was the darkling beetle).
In Spencer’s first survey in 2014/15, GPS tracking concluded there were at least 550 redback spiders in the reserve, most concentrated around clusters of unused rabbit holes.
The reason for this is that the rabbit holes provide the ideal place for redbacks to build webs to catch the beetles and reproduce, Spencer says.
Over a two-year lifespan a single female redback typically produces four egg sacks a season each containing about 200 spiderlings, she says.
After removing 15 female spiders from rabbit holes, filling them in and releasing the spiders, four months later none were living in the vicinity of the filled-in holes..
Spencer’s latest count put numbers at about 112 females largely thanks to her efforts.
‘‘We can definitely cut the numbers back [but] the spiders are definitely still there and I think it’s going to be an ongoing battle really.’’