Noble False Widow Spider Captures a Pygmy Shrew in Southern England

Most spiders present very little threat to people, and that includes the much-maligned noble false widow (Steatoda nobilis).

Yet this 1.4-centimetre predator can perform remarkably beyond what its size might suggest. A 2023 study indicated that noble false widow spiders may routinely hunt vertebrates, with recorded prey including lizards, bats and, more recently, shrews.

The study's authors documented the latest case at a grisly site outside a bedroom window in southern England. There, a female noble false widow overpowered and ate a pygmy shrew (Sorex minutus).

Although its name suggests otherwise, a pygmy shrew is enormous beside the spider. It normally measures roughly 5 centimetres in body length, with a tail about 4 centimetres long.

Excluding its tail, the shrew is more than three times the length of a 1.4-centimetre noble false widow and has around 10 times the spider's mass.

How the noble false widow catches larger prey

Vertebrates commonly feature in the diets of larger spiders, including tarantulas. For smaller species such as the noble false widow, however, reptiles and mammals present a very different challenge, as they cannot physically overpower them in the way a tarantula can.

Instead, like the true widow spiders - including the notorious black widow and redback spiders - the related noble false widow uses a combination of highly effective venom and exceptionally strong silk to subdue prey much larger than itself.

This was the strategy seen at a house in Chichester, southern England, where Dawn Sturgess, a zoologist at the University of Galway, captured the extraordinary footage below:

The recording shows a noble false widow web outside the home's bedroom window, containing a small mammal caught in the silk. Researchers later examined the remains and identified the animal as a pygmy shrew.

The pygmy shrew trapped in silk

Researchers reported that the shrew was still alive while entangled in the web, although it made only a handful of faint movements early in the incident. This was probably the result of the spider's potent neurotoxic venom, which is known to bring about rapid neuromuscular paralysis.

The spider repeatedly travelled between the shrew and the rafters above the window, using silk to raise the shrew approximately 25 centimetres, according to the researchers.

Within 20 minutes, it had hauled the prey into the rafters, where it was partly hidden from view. The spider then swathed the shrew in silk, fed on it for three days, and finally discarded the remains from its web.

According to the researchers, "the remains of the shrew were nothing but fur, bones, and skin".

How the spider initially captured the shrew remains uncertain, though it was likely not a chance encounter.

This marks the third report in five years of a noble false widow catching a vertebrate. The spiders' techniques suggest adaptations for "habitual vertebrate predation," the researchers noted in their study.

"This observation demonstrates further that the noble false widow is perfectly adapted to take down large prey, combining potent venom, extremely strong silk, and complex hunting behavior," said lead author Michel Dugon, a zoologist at the University of Galway.

The researchers suggested that the shrew probably climbed a wisteria plant near the bedroom window. The spider then caught it with silk, paralysed it with venom and lifted it into the rafters.

A first for false widow spiders in Britain and Ireland

The study authors said this is the first recorded instance of any spider in the Theridiidae family preying on a shrew in either Ireland or Britain.

It is also the first reported case anywhere in the world of any false widow spider species feeding on a shrew.

Native to Madeira and the Canary Islands, the noble false widow has spread as an invasive species to several other regions during the past century. It is perhaps best known in the UK, where misleading tabloid reporting has wrongly portrayed it as a lethal danger.

Although a noble false widow bite can be painful and may introduce pathogenic bacteria alongside its neurotoxic venom, the spider is neither aggressive towards people nor deadly to them. It represents less of a public-health risk than some news reports imply.

Nevertheless, as an invasive species, it could potentially create difficulties for both people and wildlife. Learning more about this remarkable arachnid is therefore sensible.

"The noble false widow is a very intriguing spider, and we have much to learn about it still," said senior author John Dunbar, a zoologist at the University of Galway.

"We are very grateful to the members of the public who share their observations with us. This allows us to understand better how this invasive species may impact us and our environment."

The study appeared in Ecosphere.

An earlier version of this article was published in March 2023.