Here is a nice story about these pretty ladies. The name 'ladybug' is similar throughout European languages and is derived from (our lady) Mary. She was often depicted wearing a red cloak with seven black dots, which would represent Mary's seven joys and seven sorrows. Names in other languages also refer to Christian religion, but also to fertility. Also think of the Dutch name: 'lieveheersbeestje', where the name of this little animal is preceded by 'dear lord'. So far, thank you, Wikipedia.
With this information, ladybirds seem quite spiritual little insects to me; they refer to something holy, fertile, revered. It fits perfectly with their greatest ability: they eat plant lice, mites, thrips and all kinds of insects that harm our vegetables and can devastate whole harvests. Imagine that in times when people really depended on their crops and when pesticides did not exist, it was a real godsend when ladybugs showed up and controlled nasty pests.
To attract these respected insects, make sure you have a nice warm place where ladybugs can overwinter. Also, create little shelters (of bricks, stones or earthware) with twigs and hollow straws in which they can hide.
By the way, did you know that ladybirds are protected by royal law in Belgium? It mentions the interdiction to kill, torment or capture ladybugs. Thus, welcome our ladies with respect, and you will reap your rewards*.
*(hmm.. this proverb is actually more fitting in Dutch, where it says 'you will reap the fruits').