Fire ants are extremely rare in Michigan.  If you are referring to the color there are several that fall into that category and can be mistaken for fire ants.  Since they were under a brick they could be thief ants or pavement ants.  Pavement ants will nest under anything that provides warmth from the sun including rocks, sidewalks, patio bricks etc.  Most ants are not harmful to garden plants, they are just annoying.  If you find them on your plants they are looking for anything sweet, nectar or sap.  Ant populations can be reduced with insecticides found at your garden store. Be sure to read and follow all instructions and safety precautions found on the label before using any pesticide, especially where children or pets may be present.  You can also try using   generous amount of diatomaceous earth labeled for insect control around the colony entrance. You will kill enough of them to cause the rest of the colony to move to another location. The diatomaceous earth powder will not harm you or the soil. It will kill other crawling insects until it rains.  Again, follow label cautions and directions.   

 If you would like to identify the type of ants you can send in a sample to the MSU diagnostic labs for a positive id.   They are requesting pictures before sending in samples. Images can be sent to <personal data hidden>. Call ahead for instructions on the best way to send in a sample.   They can be contacted at<personal data hidden> or online at:

https://pestid.msu.edu

 More information:

https://extension.umn.edu/insects-infest-homes/ants#nonchemical-methods-of-getting-rid-of-ants-41810

https://hortnews.extension.iastate.edu/pavement-ant

https://www.canr.msu.edu/resources/pavement-ants

https://ecommons.cornell.edu/bitstream/handle/1813/43841/pavement-ants-FS-NYSIPM.pdf?sequence=1&isAllowed=y

https://www.canr.msu.edu/resources/thief-ants

I hope this helps you out and if you have any further questions don’t hesitate to contact AaE again.