Ireland’s large spider invader is starting to eat unlikely native species

26 Jul 2018

The noble false widow spider, which has colonised much of Ireland. Image: NUI Galway

The first recorded instance of one of Ireland’s creepiest invasive species eating an indigenous one has been discovered.

The legend goes that St Patrick drove the snakes from Ireland. If a new discovery is anything to go by, we might need him again, but this time to drive away a recent invasive species.

First found in Ireland 20 years ago, the noble false widow spider is originally from Madeira and the Canary Islands off the coast of Africa, but over the years spread across Europe having hitched a ride with human travellers.

Now, in a paper published to the Proceedings of the Royal Irish Academy, a team from the Ryan Institute at NUI Galway has documented the first evidence of the spider feeding on a reptile species native to Ireland.

Can hurt humans

The discovery was made in the back garden of a home in Killiney, Co Dublin, in May 2017 when a 8.5cm juvenile viviparous lizard was found entangled in the web of a 3.3cm noble false widow spider feeding on its flesh.

Such a scene is not uncommon elsewhere in Europe as the spider is remarkably adaptable and possesses fast-acting neurotoxic venom. When administered to its prey, it causes neuromuscular paralysis in terrestrial vertebrates, and it occasionally feeds on small reptiles.

While not thought to be life-threatening to humans, a bite from its fangs can cause pain and discomfort for a few days.

Viviparous lizard

Ireland’s only native terrestrial reptile, the viviparous lizard. Image: NUI Galway

What this finding means

Unlike many of Ireland’s native spiders, which tend to live for around a year, the noble false widow can live for up to seven years.

Rather than just being a curiosity, however, Dr Michel Dugon of the Venom Systems Laboratory in the Ryan Institute said this discovery was significant for two reasons.

“One, it is the first time a terrestrial vertebrate has fallen prey to a spider in Ireland; and second, the viviparous lizard is a protected species in Ireland while the noble false widow is a recent alien species that is still actively colonising Ireland,” he said.

“This poses the question of the delayed impact of overlooked invasive species on iconic native organisms. It also raises the question of the true impact of the noble false widow on our native ecosystems.”

Looking across Europe, lead author of the study, John Dunbar, added: “While black widows are known to prey on small reptiles, there are only two previous accounts from other species of false widow spiders preying on a lizard in Iran and on a snake in Bulgaria.”

If any readers happen to come across some noble false widow spiders or viviparous lizards in Ireland, you can report sightings to Dugon here.

Colm Gorey was a senior journalist with Silicon Republic