Small, creamy-white with a single black spot on each wing for males or two for females. A butterfly that is a gardener's nemesis. The cabbage white looks innocent enough as it flutters lazily over the lettuce patch. But beneath that delicate exterior lies a voracious appetite that has frustrated vegetable gardeners for nearly a century. A butterfly that is a pest. The female is a relentless egg-layer. She sticks tiny, yellow, bullet-shaped eggs to the undersides of cabbage leaves, one at a time, working her way across the patch. Within days, these hatch into velvety green caterpillars that chew holes through leaves with alarming efficiency. A single caterpillar can skeletonise a leaf. A dozen can eat the whole plant down to the stem before vanishing into the soil to pupate. Unlike native butterflies that specialise in specific host plants, the cabbage white is a generalist within the brassica family. It breeds rapidly, with multiple overlapping generations in a single summer. This allows populations to explode when conditions are right. They are strong fliers too, capable of crossing vast distances to find new food sources, making them impossible to exclude from any garden. Their flight pattern is erratic and bouncing, a float-and-drop motion that makes them hard to catch but easy to spot against the dark green of the crops. The caterpillars are masters of blending in, their green bodies matching the leaves perfectly. They are also the target of a biological arms race. Tiny parasitic wasps lay eggs inside the caterpillars, eventually killing them, a natural check that gardeners rely on. To the home gardener, the cabbage white is a nemesis, a symbol of the constant battle to protect food from the hungry hordes. The vegetable patch is green. The cabbage white flutters, innocent-looking, landing on a cabbage leaf. She lays eggs. The caterpillars hatch. The leaves are eaten. The gardener sighs. The butterfly does not know it is a nemesis. It does not know it is a textbook example. It just wants to lay eggs. To the ecologist, it is a textbook example of a successful invasive species, one that arrived by accident and made itself at home. The cabbage white is proof.