Be social like these insects

This is the picture of group of insects grouped in a colony. It was very interesting to see all the small insects colonizing themselves and getting close to each other forming a very smooth surface. When the move due to disturbances, individual insects can be seen but in some minutes they again come close together to form the colony. I don't know exact scientific or common name of this animal but if you know, let all know. The insect look like ants but I didn't check the number of legs to confirm whether they are ants or spider. They are lying in cemented wall.