The large thistle aphid Uroleucon cirsii is between 4 and 5.2 mm in length and has characteristic two tone legs.

Dark-tailed Thistle Aphid (Uroleucon aeneum) is similar and also uses Thistle as a host plant, but Uroleucon aeneum has an all black cauda (tail) whereas the cauda is dusky yellow in Uroleucon cirsii.

A close up photograph is needed showing the cauda (tail).  Please also state the host species.

Found on thistles especially Creeping Thistle.

Summer.

It lives on the leaves and stems of some thistle species, especially Creeping Thistle.

Not well recorded in Britain

Status in Leicestershire and Rutland not known.

https://influentialpoints.com/Gallery/Uroleucon_cirsii_Large_thistle_aphid.htm