Observations of hoverfly migrations show that they can travel more than 100 kilometres per day (Witze 2018). Marmalade Hoverflies or Episyrphus balteatus, migrate from Northern Europe to Southern Europe, before returning to Northern Europe each year (Witze 2018). Adult hoverflies pollinate flowers, whilst larvae eat pest insects such as aphids (Witze 2018). However, their migration is typically only noticeable when they are funnelled through the narrow opening of mountain passes (Witze 2018). Additionally, an increase in rainfall leads to an increase in plant and weed growth, which increases populations of pest insects such as aphids (which stunt plant growth), and their predators, such as hoverfly larvae (of which there are around 6000 species), lacewing larvae and ladybirds (lessard and Yeates 2016).
Lundmark, C. (2010) Long Distance Insect Migration. Bioscience, vol. 60, no. 5, pg. 400. Available from: https://academic.oup.com/bioscience/article/60/5/400/238148
Blakemore, E. (2015). Norway is Building a Highway for Bees, Smithsonian.com, viewed 10th May 2018, https://www.smithsonianmag.com/smart-news/norway-has-highway-bees-180955703/
Witze, A (2018) Flying insects tell tales of long-distance migrations, ScienceNews, Vol 193, No. 7, p. 22. Available from: https://www.sciencenews.org/article/flying-insects-tell-tales-long-distance-migrations
Lessard B and Yeates, D (2016) From Warm to Swarm: why insect activity increases in summer, Australian Geographic, viewed 11th May 2018, available from: http://www.australiangeographic.com.au/topics/science-environment/2016/12/experts-predict-increased-insect-activity-this-summer