Ok, I have a conclusion to this discussion! Officially, these bugs hold at least 3 names in English. In North America, they are called ladybugs. In the UK, they are called ladybirds. Scientist like to call them lady beetle and beetle is a common name all over the world for them.
They keep that name (to most non scientist) no matter if they are red with black spots or yellow with black spots.
In French, these bugs are known to be God's bugs because a lot of them used to be found at the bottom of crosses in the Medieval era. In English however, even if a superstition has always said that beetles are a sign of luck, they were never known to have any relation with God.
This is the summary of all the discussions that I've had over the past week about beetles.
Thanks to everyone who has participated in this discussion and if you would still like to bring an input in it, you are more then welcome.