GWD3 Q2题目看不懂

Yellow jackets number among the 900 or so species of the world’s social wasps, wasps living in a highly cooperative and organized society where they consist almost entirely of females—the queen and her sterile female workers.

"yellow jackets number among the 900 or so species of the world's social wasps..."

这里的number是什么意思呢？

谢谢！！！