Either they want to hide from predators, or just like the taste of ants, or just want to disguise themselves as an ant. Lots of spiders look so similar to ants that you can barely tell the difference, until they eat you!
Hope this helped and these images are some proof:




In the first picture, there is something really interesting, it looks like there are two spiders, but in fact it’s just one. It’s has over sized jaws to spar with other males and show off to the females, but since the ants don’t have monstrous fangs, the jaws themselves are disguised as an entire second ant.
The last photo is a Myrmarachne plataleoides, also called the Kerengga. It’s a jumping spider that copies the Kerengga or weaver ant in morphology and behavior. This species is found in India, Sri Lanka, China and many parts of Southeast Asia.
A good thing about these ant-like spiders is that they don’t bite people.
The body of the M. plataleoides appears like an ant, which has three body segments and six legs, by having constrictions on the cephalothorax and abdomen. The males resemble a larger ant carrying a smaller one.
Posted by Farnam