to only feed on two plant sources: the alder buckthorn (Rhamnus frangula) and the common buckthorn (Rhamnus carthartica). This influences the distribution of the adult brimstone, as the presence of these two buckthorn species is necessary for the survival of their offspring. Adult Unlike their larval forms, which are specialised for particular host plants, adult brimstones are not specialised nectar feeders. The common brimstone heavily feeds on the nectar of several flowering species including knapweed (Centaurea jacea) and scabious (Knautia arvensis and Succisa pratensis). However, brimstones have also been observed feeding on the nectar of coltsfoot (Tussilago farfara) in April and May and have been recorded gathering nectar from many other species of flowers. Adult food plant availability is another factor that is important for habitat selection. Parental care Oviposition The common brimstone is univoltine, meaning that it lays one generation of eggs each year. There are several ideal characteristics of the particular host plants chosen for oviposition. Adult brimstones lay eggs on the underside of the leaves of the two species of host plants, where they are less conspicuous. The high mobility of G. rhamni enables the butterflies to find even the most isolated host plants in an area, which are more ideal for their offspring. Eggs are more likely to be deposited on outlying plants, leading to reduced vulnerability as fewer predators are attracted to these plants. Another factor is damage; undamaged plants indicate the absence of other eggs, as brimstone larvae leave holes in the leaves of the plants on which they feed. Since predators and parasites are attracted to damaged plants through chemical or visual signals, less damage leads to greater offspring survival since eggs are less likely to be detected. Plants exposed to both sunlight and the open lead to reduced chances of predation and parasitism as well, and are more accessible to adult butterflies. Larvae can also benefit from decreased host plant defences; juvenile plants and plants with late bud-bursts produce fewer toxic defence chemicals, as resources are directed more towards plant growth. Life cycle The common brimstone is one of the longest-living butterflies, with a life expectancy ranging from 10 months to a year. Due to its hibernation and life cycle, it has one generation per year. Development from the laid egg to the emergence of the imago is approximately 50 days. However, the adult brimstone spends a large portion of its life