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Extreme weather events are becoming more frequent due to climate change. We therefore need to understand how species respond to these events. In 2018, the worst drought ever recorded hit the island of Gotland in the Baltic Sea, which led to a major decline of the threatened marsh fritillary (Euphydryas aurinia) the succeeding summer. We compared yearly occupancy among 256 habitat patches between 2018 and 2020 and analysed the colonisation-extinction dynamics between 2019 and 2020 in relation to patch area, connectivity, and habitat quality. Moreover, using capture-mark-release data in two patch clusters differing in connectivity, we also compared population sizes before and after the drought and analysed population growth rates. We also compared yearly abundance of host plants (Succisa pratensis) over time. Results show a remarkable recovery of the marsh fritillary. Both patch occupancy in 2020 and the number of individuals in the well-connected patch cluster were higher than before the drought. In contrast, host plants were fewer and smaller, which taken together suggest that the amount of food resources was roughly half in 2020 compared to the pre-drought conditions. Moreover, the butterfly population in the less connected patch cluster was eight times smaller compared to the population size before the drought. Local colonisations, extinctions, and population growth rates were explained by connectivity. The ability to quickly recover after extreme droughts is promising in times of climate change. The significance of connectivity for the population dynamics during recovery highlights the importance of maintaining well-connected patch networks. Funding Agencies|Cementa AB; Stiftelsen Oscar och Lili Lamms Minne [FO2020-0023]; Svenska Forskningsradet FormasSwedish Research Council Formas [2018-02846]

British pollinating insects are vital for their contribution to crop yields as well as maintenance of semi-natural environments across the UK. The Syrphidae family are highly diverse and thought to be an important pollinating group. In order to understand the evolutionary relationships in this family, mitochondrial genomes were used to build the largest tree of the Syrphidae family to date. This tree was used to establish relative ages for divergences within the family, and to explore the evolution of diverse syrphid larval life histories. The recent introduction of a UK pollinator monitoring programme has resulted in a large amount of data with the potential to inform conservation and management, presenting an opportunity for DNA analysis. A CO1 reference database was curated and tested for UK syrphids, resulting in sequences for 70% of UK species and highlighting difficulties in DNA identification. Barcoding of syrphids was then expanded by also metabarcoding pollen from gut samples. This showed the diversity of plant – syrphid interactions at an individual level across three different land use types. It also highlighted the importance of including syrphid larval life histories in analyses of this family, as these appeared to have a larger effect on species composition than pollen composition did. Finally, the reach of this thesis was expanded to include non-bee and non-syrphid pan trap visitors from the pollinator monitoring programme. This highlighted the diversity of non-syrphid Dipterans and allowed species and phylogenetic diversity to be compared in these bulk insect samples. Using DNA methods to analyse monitoring data has the potential to increase our knowledge of cryptic species, phylogenetic diversity and pollinator associations. Alongside this, DNA can be used to analyse large datasets of diverse pollinating insects which otherwise would be overlooked. Open Access