during my daily inspection, I came across a small, slender alien on my lime tree — greenish-red, long-legged, and still as a statue. He stared back, unafraid of the curious giant leaning in. I ran inside for my camera and, after a few clicks and a quick round of googling, realised my rooftop visitor wasn’t local at all. He was, in fact, an assassin on the rooftop — a well-travelled immigrant from foreign lands.
Background
We often imagine invasions arriving with ships and trade routes. Sometimes, though, they come quietly, hidden beneath the leaf of a nursery plant — until one morning, they’re hunting on your citrus.
Zelus renardii belongs to the assassin bug family (Reduviidae, subfamily Harpactorinae). Originally native to Central and North America — from the southern United States to Honduras — this species has become a cosmopolitan traveller thanks to the plant trade and its remarkable adaptability to urban gardens.
It was first reported in Europe in the early 2010s, appearing in Greece, Spain, and Italy before spreading across the Mediterranean to Turkey, Albania, Sardinia, and France. In Portugal, its presence was confirmed in 2020, when Nelson Conceição photographed a specimen at Lota Beach (Altura, district of Faro, Algarve) — the westernmost record in Europe so far.
Description
Adults are slender reddish-brown insects with long legs and a distinctive X-pattern on the back. They often rest beneath leaves or along flower stems, motionless and patient. Their forelegs secrete a sticky resin that helps them immobilise prey — a hallmark of the Zelus genus and one of its evolutionary secrets for success.
Lifestyle & Diet
A true generalist predator, Z. renardii feeds on a wide range of arthropods — aphids, leafhoppers, and thrips, but also beetles, caterpillars, and even other beneficial predators such as ladybirds and lacewings.
When it spots a target, it raises its forelegs and antennae, then launches a lightning-fast ambush. Luckily, we merely exchanged glances before he moved on, pausing just long enough to pose for my photos. Feeding can last more than an hour — patient precision at its finest.
Because it preys indiscriminately, its impact on ecosystems is double-edged: helpful in keeping pests under control, but potentially harmful to native beneficial species.
Ecological implications
Though harmless to humans, Z. renardii is considered an alien species in Europe. It thrives in Mediterranean climates — with nymphs developing best between 25 °C and 30 °C — and easily colonises urban green spaces, orchards, and rooftops that mimic its native environment.
Its rapid expansion has been linked to the movement of nursery plants (where females glue egg batches under leaves), its broad diet, and a tolerance for irregular food supply — though not, I should note, on this rooftop!
Closing Thought
Whether friend or foe, Zelus renardii seems here to stay — a reminder that even the smallest corners of our gardens are crossroads of the world. He has been officially labelled a “Rooftop Friend.”
How about you? Have you seen one? Share your sightings — I’d love to know if this silent immigrant has visited your garden too.
P. S. Curious about more rooftop stories? Find other RUG posts here.
