Never where you want them!

As I have mentioned a few times on GC, I have an area of land which I am trying (hard!) to put back to a bit of field after having had commercial kennels, concrete paths, you name it on it.
We are very close after 2 years of blood sweat and tears to having the area good enough to be sown with grass. I intend to do this at the end of this month.
Currently the area which is about 1/4 acre is supporting a very healthy crop of weeds. These will be dealt with just before sowing the grass.
Today I noticed the magnificent crop of Groundel is just about to set seed so thought I'd hand weed the copious amounts before they shed loads of seed. The weeds are smothered with Lady Birds. Can't see any green fly or other insects for that matter for the lady Birds to feed on. Why the hell are they there? Not a sign of any in the garden...typical.