Why did the Monkey King kill Spider Spirit?

The reason is that this spider spirit tried to eat the Tang Priest and live forever. The Monkey King killed Master to save him. The details of the story are as follows:

In the Journey to the West, Tang Priest strayed into Pansi Cave and was captured by Spider Spirit. The Monkey King tried not to fight with women. When Spider Spirit took a bath, he took their clothes by magic. Then, Zhu Bajie was fascinated by beauty, accidentally entangled in the silk leaked by Spider Essence, and was also taken away by Spider Essence. After that, Spider Spirit sent someone to send Tang Priest to Huanghuaguan to share Tang Priest's meat with their brothers. Spider essence catches Tang Priest and Pig Bajie with spider silk, and then shares it with centipede essence. Finally, in order to save the master, the Monkey King killed the spider spirits one by one.