Drive through the Mackenzie Basin in summer and the lupins are hard to miss, with purple, pink, blue, yellow and white flowers lining roadsides and riverbeds. Tourists photograph them, bees work through them, and at the same time conservation workers are trying hard to control them.
Russell lupins, Lupinus polyphyllus, come from North America. The colourful forms seen here are linked to garden plants that later escaped cultivation and were also deliberately spread in some places.
The problem becomes clear when they move into braided rivers. These rivers may look bare, but that open gravel is important habitat, with channels that shift, floods that move stones and new islands that constantly form. Birds including kakī/black stilt, ngutu pare/wrybill and tarapirohe/black-fronted tern depend on these open spaces.
Lupins can form dense stands, trap sediment and turn bare gravel into thick vegetation, reducing nesting habitat and giving predators more cover.
The bees certainly use them, especially for pollen, but our bumblebees were introduced too. They were brought here because farmers needed better pollination of crops such as clover.
That is what makes lupins such a useful part of this story. Aotearoa had been isolated for around 80 million years before people arrived, and during that time plants and animals evolved in unusual ways, many found nowhere else. For most of that history there were no land mammals apart from bats.
People later brought plants, animals and insects for farming, food, gardens and familiar landscapes. Some proved useful, some spread far beyond where they were intended, and some did both.
Russell lupins show that clearly. Bees benefit from the flowers and people enjoy looking at them, yet the same plant can still damage a native ecosystem.
Today lupins are actively controlled in parts of Canterbury, including Mackenzie Basin waterways, because protecting those braided-river habitats matters more than keeping the colour.
They are beautiful, the bees love them, and in the wrong place they are also a serious ecological problem.