On a June morning in a suburb of Stockholm, after the first sustained rain in weeks, the flagstones of a garden glisten with fresh trails. A gardener, coffee in hand, spots the dark, ridged body of a killer slug—Arion vulgaris—inching toward the hostas. For much of the dry spring, such sightings had been rare, a small mercy that had gardeners daring to hope. But the rain has summoned the survivors, and with them, a new round of egg-laying. Ted von Proschwitz, a slug expert at Gothenburg’s natural history museum, confirms what many are seeing: the dry weather had suppressed numbers, but the coming weeks’ rainfall will decide whether the respite holds.

The killer slug, an invasive species that has troubled Swedish gardens for years, is just one actor in a wider drama. Across the world, pests are responding to a changing climate with a speed that often outstrips human countermeasures. In Indonesia, where the fall armyworm first struck cornfields in 2019, rising temperatures have accelerated the insect’s life cycle, making it more voracious and expanding its range. Research cited by Indonesian agricultural agencies indicates that each one-degree Celsius rise in average temperature can increase yield losses in staples like maize, rice, and wheat. The same warming that lengthens growing seasons in northern Europe also allows invasive ants to survive London winters, as entomologists in the UK have observed with the Argentine ant.

The responses are as varied as the landscapes. In Nigeria, where the wet season brings a surge of aphids, whiteflies, and caterpillars to vegetable farms, the National Horticultural Research Institute promotes organic methods: neem extracts, garlic sprays, and the encouragement of beneficial insects like ladybirds and lacewings. Farmers are urged to scout their fields weekly, removing infected leaves before infestations explode. In Australia’s Central Tablelands, the fight is against feral pigs that can destroy crops and carry diseases such as foot-and-mouth. Farmer Derek Larsen spends his days setting traps and coordinating with neighbours, but he faces a modern complication: absentee landholders who, unfamiliar with biosecurity laws, leave their properties unmanaged, allowing pigs to rebound.

The battle is often intimate, hand-to-hand. Swedish gardeners are advised to take a spade on a “killer round,” slicing the slug just behind the head. But von Proschwitz also advises gardeners to spare the panther slug, a spotted competitor that will attack and even eat the killer slug. In the UK, the Royal Entomological Society warns of the Asian hornet, a predator that “hawks” honeybees at the hive entrance, and urges gardeners to report sightings so nests can be removed. The harlequin ladybird, once introduced as a biological control, now disrupts garden ecosystems by devouring native ladybirds and hoverflies. There is no single weapon, only a patchwork of vigilance, local knowledge, and grudging respect for the intricate webs these invaders exploit.

As the Swedish gardener finishes the morning round, a panther slug glides unharmed across a wet leaf, a tiny ally in a war that will never be won, only managed. The spade is rinsed, the coffee gone cold. The next rain will bring more eggs, more trails, more early-morning patrols. In a world where a dry spring can feel like a reprieve and a summer storm like a setback, the rhythm of pest and person has become a quiet, global pulse.