On this day, 74 years ago, Elizabeth and David Lack walked up to the Puerto de Bujaruelo mountain pass above Gavarnie on the border of France and Spain in the Pyrenees. They sat with their backs against a boulder and watched the migration. They saw hundreds of birds, thousands of butterflies, tens of thousands of dragonflies. But it was only after they had been there for an hour that they realised there was another migrant. One much smaller than the others but outnumbered them all hugely. These migrants were the hoverflies. And in their paper (first photo), published exactly 73 years ago, they described them as the most remarkable migrants of all. Standing on the shoulders of these giants, the team from the @UniExeCornwall (@KoralWotton, Toby Doyle, Richard Massy, @BugsWithBarnes, @OliverPoole_, @KdaviesEnto, @_ScarlettWeston and I) have been heading to the same mountain pass every year since 2018 to continue what the Lacks' started all those years ago. Earlier this year we published our findings in a @RSocPublishing paper: royalsocietypublishing.org/d… We found that every year 17 million insects migrate southwards through the pass. We recorded five different Orders of migrants, and nearly the 90% of them were the flies! The flies were the most remarkable migrants of all.