The male of the species is that most noticeable bright yellow butterfly, that is typically one of the earliest species to be observed in spring. The less glamorous female is still readily identifiable with a closer view.
This is peak season for their egg laying. This species is a very good example of native plant dependency. The foodplant for the larvae is the Purging Buckthorn (Rhamnus cathartica) or the closely related Alder Buckthorn (Frangula alnus). Nothing else will do! In our gardens and surrounding countryside, the Purging Buckthorn is more common, as the Alder variety prefers a damper and acidic soil.
The pictures kindly provided by Tony Penycate taken in his own garden shows the female Brimstone laying eggs on the new tips of the buckthorn. The second image shows the delicate eggs attached. Look closely and you will see quite a few!