FALSE WIDOW SPIDERS are up to 230 times more poisonous than native Irish species, new research has found.
The research, conducted by scientists from the Ryan Institute in NUI Galway, looked at how the species has been so successful at spreading in towns and cities worldwide.
Over the last five years, the team at the University’s Venom Systems Lab, led by Dr Michel Dugon, have been studying a wide range of characteristics specific to the species including its venom, symptoms after envenomation, ecology and behaviour.
For the study, published in the international journal Toxins, the team obtained venom yields from 550 Noble False Widows, including 125 males and 425 females.
They found that the Noble False Widow spider has venom that is up to 230 times more potent than our native species.
This may explain how the spider has spread throughout Ireland and how it can tackle a range of species much bigger than themselves, including lizards, bats, shrews, and other spiders, the study said.
Originating from Madeira and the Canary Islands, the Noble False Widow spider, formally named Steatoda nobilis, has the potential to become one of the world’s most invasive species of spider.
It was first reported in southern England in 1879, and has spread northwards towards Scotland and westward through Wales and Ireland in recent decades.
The species has also spread globally across Europe, East Asia, North America, and South America.
The research found that False Widows are active all year round with peak activity between August and November.
In Ireland, field observations showed that they are extremely common on street furniture, signposts, traffic lights, bus shelters, boundary railings of parks and graveyards, garden furniture, garden walls, pillars, and gates, regularly outnumbering native spiders.
They are mainly active after dark and typically prey on a wide range of insects and other arachnids, but has also been documented preying on a lizard in Ireland.
The species has a high reproductive rate and is capable of producing several egg sacs each year, each containing on average 98 eggs.
Population density of False Widows has not been investigated yet, but observations suggest that they dominate habitats within a few years of their arrival.
The study found that the spider can also make calculated decisions on whether to attack large or small prey depending on how much venom is left in their venom glands.
If little venom is available, they avoid taking on large opponents that could injure them, and instead focus on smaller prey.
The spider will also make calculated decisions in battle, targeting the most innervated body parts of its enemy, where the neurotoxic venom is most efficient.
Over the course of the study, the false widow spider killed and ate 95% of its opponents.
“The Noble False Widow spider is a truly remarkable animal; at every turn this species has surprised us in its ability to become globally invasive and dominate habitats it occupies,” said Dr John Dunbar, Irish Research Council Post-Doctoral fellow and co-senior author of the study.
“The tiniest amounts of venom – about 1,000th of a raindrop – can cause medically significant symptoms in humans that are about 250,000 times larger than them. Each new study brings us closer to understanding how exactly they are achieving their success.”
Joint first author of the study and NUI Galway graduate, Sean Rayner, said: “Over the past number of years we have seen a noticeable increase in Irish populations of Noble False Widow. This study will help us further understand what makes them so successful and hopefully highlight their potential impact to our ecosystems.”
Aiste Vitkauskaite, researcher at the Venom Systems Lab and a joint-first author of the study, said: “This is an important study which provided evidence of the Noble False Widow’s superiority as a competitor in terms of its venom and predatory strategies against the native spider populations in the laboratory setting.
“We are hoping that our findings will lead to wider field-based studies to quantify the true impact of this alien species on native arachnids.”
The team of scientists are encouraging members of the public to email them at falsewidow@nuigalway.ie to report sightings of the Noble False Widow spider.
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