This is a fairly common red ant, and one which I tend to find in the grass verge out the front of my house when cutting it. The workers are 4-6mm (around 1/4 inch) long. I found difficulty in identifying them specifically, but with help and due thanks to Mike Fox from BWARS for confirming Myrmica ruginodis.
They are found in various habitats including woodland, grasslands and gardens. Common and widespread throughout great Britain, and probably our most commonest ant.
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August 2017, front grass verge, Staffordshire, England.