Fly on globe thistle

Popped into the garden to see if there was anything of interest. No butterflies (again). A few bees, but nothing quite worked out. Various flowers, but settled on this as for once, the 100mm prime lens has done a pretty good job. No idea what the fly is - Google throws up a few suggestions, including Hylemya, a genus of root-maggot flies. Whatever it is, it's not very pretty! Hopefully the butterflies will make an appearance before too long.