A. Scale are insects have soft bodies and can crawl around from place to place when they are young. They are called “crawlers” at this stage in their life.
Once they find a place to live, they build a house covering itself called a “scale”. Underneath that scale the soft bodied insect is protected and sucking plant juices. Until it exits the scale to reproduce.
The scale covering on its outside protects it from predators as well as contact insecticides. Ants move crawlers to new locations just like they will aphids. The trick in controlling them is to catch scale insects in their "crawler" stage, when they are susceptible to just about anything including soap sprays.
The most effective sprays are considered spray oils; horticultural oils, supreme oil, dormant oil, a bunch of different names. Many of them are petroleum oils derived from paraffin or mineral oil.
It's a good idea to apply these oils twice during the winter and again in the spring before or after flowering. There are sticky traps available that catch crawlers to identify when to spray. If traps are not used, repeat applications of spray oils during winter and spring is very effective.