Lady bugs and aphids

[gallantwarrior]

Not knowing where else this might fit, I thought I'd try here.
So, I came across a HUGE bunch of lady bugs on one of my fence rails today. Hundreds of them. They had a few aphids with them, too. Since the fence rail is made of kiln-dried 2x4 lumber and I assume has little nutritional value for either the lady bugs or the aphids, here's my question:
Do the lady bugs move their aphid "herds"?

 

[Old Rocks]

Did you try googling 'lady bugs'?

 

[gallantwarrior]

I did. I found no real information about why they are inhabiting a wooden fence.

 

[Moonglow]

free rent

 

[whitehall]

Apparently the lady bugs were imported to control the spread of aphids way back in the early 1900's. Unlike other introduced species it seems the bugs do little harm except for ending up in attic windows in droves during certain times of the year.