Brimstone butterflies are one of my favourites. I'm not a very clued up lepidopterist, but Brimstone butterflies I can ID a mile off. They're yellow - the books say the males are rich yellow and the females lighter, although to my mind they're yellowy green. I saw my first of the season on a run yesterday, in between yelling at the dogs and feeling genuinely hot for the first time this year. She was unmistakably yellow (green), and with the shape peculiar to Brimstone butterflies. She was fluttering about along a woodland margin - very typical. They're not only easy to spot, but one of our most attractive and long lived butterflies too. See Brimstone butterflies at this time of year and they'll be adults emerging from hibernation, a real harbinger of spring. The next generation start flying around August.
I particularly like them because of their relationship with Buckthorn. Brimstone butterflies' larvae feed exclusively off our native Alder Buckthorn and Purging Buckthorn, Rhamnus frangula and Rhamnus cathartica. If you grow them, as we're doing, chances are you'll find Brimstones moving in sooner rather than later. They stay for successive generations, year after year. Buckthorn is critical for Brimstone butterflies' survival. There are many other similar exclusive relationships between our native flora and fauna. Insects don't just need flowers to provide nectar and pollen; they often have other demands on them too. These mean it's easy to play God. If you want Brimstone butterflies, plant Buckthorn. Small Blues? Kidney Vetch. I love the sort of immediate cause and effect you can get in your garden. Buckthorn is a nice easy-to-grow native shrub anyway. We're growing Alder Buckthorn here, as it copes so well with our waterlogged clay. Purging Buckthorn is more of a chalky soil lover, so wherever you are, you can give Buckthorn a try!