In recent years, the large heath butterfly has undergone a considerable decline throughout much of its European range. In consequence the species is now classified as vulnerable in a European context, although the butterfly is still locally common in northern parts of the United Kingdom. The majority of English colonies are located on expanses of blanket bog in the county of Northumberland, although recent extensive surveys have shown that substantial numbers of colonies have been lost from this area within the last twenty years. C. tullia is one of only four butterfly species with a southern limit to its British distribution, suggesting that climatic change may constitute an additional threat to that faced by many other butterfly species, namely habitat destruction. This thesis consists of an autecological study of C. tullia. Research showed that adult butterflies were most abundant in areas where vegetation was relatively short and sparse. Females oviposited more frequently in short, sparse vegetation than they did elsewhere, suggesting that observed female microdistributions may be consequential of their ovipositional requirements. It is suggested that eggs laid within such areas will experience warmer micro climatic conditions than those laid in taller vegetation, as will resultant larvae. Most sources in literature suggest that large tussocks of the foodplant hare's-tail cotton grass (Eriophorum vaginatum) (L.) are an important requirement of the species. The current study shows that large tussocks are of much lesser importance than previously assumed on sites that are not prone to flooding. The efficacy of heather cutting as a habitat management strategy was investigated. Higher numbers of male butterflies were recorded in cut areas, while the oviposition rates of females within cut areas were higher than in uncut controls. It is therefore suggested that heather cutting renders overgrown habitat more suitable for adult butterflies, and would therefore constitute an effective conservation management strategy on certain sites.The mobility of adult butterflies was investigated. Males were found to move for greater distances than females, and were found to be capable of dispersion between sites separated by 500m of unsuitable habitat. Females were found to be extremely sedentary, and no between-site movements were detected. It is therefore suggested that gene flow between populations at Border Mire sites is probable, although colonisation of remote sites is not. A series of absolute population estimates were made at three study sites. These data were significantly related to same-day relative estimates made using transect counts, although the relationship was not sufficiently close to confidently predict absolute values from transect counts alone. However, were more time devoted to a similar study, it is probable that this outcome could be achieved. The annual abundance at each site was calculated for each of the flight periods 1999-2001 inclusive. A life table study, investigating mortality in the pre-adult phases, was undertaken. Essentially, this study revealed that egg mortality and pupal mortality rates were both low, while larval mortality, particularly of the first instar was relatively high. Causes of mortality were not confirmed. Dissection of freshly emerged females suggested that females are probably capable of producing 65-90 eggs during their lifetimes. Adult feeding behaviour was studied. The preferred nectar source of both sexes was cross-leaved heath (Erica tetralix) (L.), although other nectar sources were also used. A study of post-copulatory behaviour revealed that females commenced oviposition prior to feeding. The importance of nectar to the butterfly was investigated by means of a trial using captive female butterflies. A group of females provided with food in the form of sucrose solution produced a similar number of eggs to a group of identical size provided only with water, suggesting that nectar availability is of less importance than has been shown for some other butterfly species.