Where are all the Hoverflies?

During the hotspell in March my garden was buzzing with Hoverflies, now there hardly seems to be any just the smaller species and few Bumble or Honey bees. The only butterflies I've seen so far are one Orange tip and a couple of green veined whites. None of which bodes well for the birds when they have hungry chicks to feed.

My lawn is covered in buttercups and they look wonderful.

Just thought this looked lovely in the sun.

A little herbaceous Potentilla