Thousands of Caterpillars

Just outside of Ormeau Park we saw thousands of these tiny green caterpillars. Does anyone know what kind they are?

Yesterday we saw the placemats in the extra in the vintage shop where we got the dress. It looked so familiar to me that I sent the photo to my mum and asked if we had something like it home. She told me we had the exact same one, but was a bit confused.
A friend had got it for her after returning from a trip from South Africa. However, my mother was told that the friend made the placemats by cutting up fabric....

Seems the friend may have distorted the truth!