while patrolling the rooftop, I noticed a small glint running upside down on an almost invisible thread — a rounded abdomen catching the light, fast as lightning. I leaned closer and there she was: elegant and poised beneath the lime leaves. Not the dangerous creature headlines warn you about, but a quiet architect working deep within her scaffold web.
I fetched my camera, and she did what false widows do best: she didn’t move, she didn’t posture — she simply watched. It took only a moment of comparing markings to realise my newest rooftop tenant was Steatoda nobilis, the noble False Widow — a species that, like many of my visitors, has travelled far before choosing this place to call home.
Background
The False Widow belongs to the cobweb spider family (Theridiidae). Despite the dramatic press it often receives, this species is not aggressive and rarely bites. Originally native to Madeira and the Canary Islands, it has spread across Europe thanks to the global movement of goods, especially ornamental plants.
Recent records collected through Biodiversity4All and other citizen-science platforms show Steatoda nobilis rapidly expanding across Europe — with new sightings clustered along the Atlantic coast, the Mediterranean corridor, and increasingly inland, particularly in warm, sheltered urban environments. My rooftop, it seems, has just joined the map.
Description
Once you know what to look for, this species is unmistakable for their rounded and glossy abdomen, cream or pale brown markings, often resembling a stylised skull or mask and dark reddish-brown legs. They prefer cracks, overhangs, and sheltered corners.
Females — the queens of the web — can reach 12–14 mm in body length, while males are smaller and more delicate. They build irregular scaffold webs with a silk-lined retreat hidden in a crevice: part tunnel, part fortress, and surprisingly strong for such a small engineer.
Lifestyle & Diet
The False Widow is an ambush predator, one of the rooftop’s most discreet pest managers. Her menu includes flies, mosquitoes, moths, beetles, lace bugs, aphids (when they wander into the web), and even small spiders.
Unlike active hunters like Zelus renardii, she waits — patiently, silently — gripping the strands that radiate from her retreat. When something disturbs the web, she performs an almost imperceptible dash, delivers a quick bite, and pulls dinner back into her retreat wrapped neatly in silk.
A master of efficiency: no wasted movement, no unnecessary risk.
Ecological implications
Although non-native in Continental Portugal, Steatoda nobilis is now well established across much of Western Europe. She thrives in human structures where warmth, shelter, and prey are abundant. Despite the hype around “false widow bites,” medically significant cases are incredibly rare. Most are no worse than a bee sting, and almost all happen when the spider is accidentally pressed against skin.
From a naturalist’s perspective, she is far more fascinating than dangerous. And from a gardener’s perspective, she is a valuable silent predator — removing dozens of flying pests every week while asking for nothing in return.
Closing Thoughts
That day on the rooftop, she held her ground — calm, steady, unbothered by my camera. Not threatening. Not fearful. Simply present. For now, she has chosen my rooftop as her watchtower.
A silent architect. A patient hunter. And officially, a Rooftop Friend.
Have you spotted a false widow on your terrace, garden, or balcony? Share your sightings — the rooftop naturalist in me is curious.
P. S. Curious about more rooftop stories? Find other RUG posts here.