Invasive false widow spiders are up to 230 times more poisonous than domestic Irish species, according to new research which helps explain their rapid spread across Ireland.
The findings shed light on the spider’s dominance: not only is its venom far more potent than any common northern European spider, but it can adapt its attack behavior to prevail in different “battle scenarios”. What exactly this might mean for the survival of other species has yet to be determined.
The research was carried out by scientists at the Ryan Institute at NUI Galway and published in the international journal Toxins.
The false widow, or steatoda nobilis, which is native to Madeira and the Canary Islands, has spread rapidly to Ireland in recent years.
Their bite usually has a similar effect on humans as a bee sting, but can often cause more serious injuries, sometimes requiring hospital treatment.
The strength of its venom, researchers say, helps explain how it tackles a range of much larger creatures, including other spiders, lizards and even bats.
Over the past five years, the NUI team, led by Dr Michel Dugon, has studied a wide range of its characteristics, including venom, bite symptoms, ecology and behaviour. During the study, the spider killed and ate 95 percent of its opponents.
“The false widow’s venom kills at much smaller doses,” Dr. Dugon said. “Essentially they have a chemical arsenal that is much stronger than native spiders. This gives them a competitive advantage because they are more toxic. So they can kill more prey with less venom and that means they don’t have to spend as much time and energy to try to produce poison.”
The species’ potential impact on Ireland’s ecosystem will be the focus of a followup study.
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“We think, but have not yet quantified, that the noble false widow has a negative impact on native species by scaring them out of their native environment,” Dr Dugon said.
The NUI research also highlights other behaviours, notably that when it has a low supply of venom, it is more selective about how to use it.
Scientists also show that in a battle, it will not inject poison at random, but will target the most vulnerable parts of the body where the neurotoxin is most efficient.
Dr. John Dunbar of the Ryan Institute’s Venom Systems Laboratory, colead author of the study, said the spider has continued to surprise scientists with its ability to become globally invasive.
“The smallest amounts of venom, about onethousandth of a raindrop, can cause medically significant symptoms in humans that are about 250,000 times their size,” he said.
“Each new study brings us closer to understanding how exactly they are achieving their success.”
The noble false widow was first discovered in England in 1879. Since then it has increased in number and scope, spreading to Scotland, Wales and Ireland.