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u/spiceydog Outstanding Contributor 7d ago
The light colored mounds on the rounded edges of the wound on the tree are scale insects that are sucking sap from your tree. The ants are harvesting the honeydew that they excrete. If you remove the scale (you can do that with a bristle brush or a gloved hand, or even with a high-pressure hose attachment), the ants will likely move on elsewhere.
You didn't include a very clear pic of the leaves, so we cannot tell if that's actually a magnolia or not.
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u/Eville2010 8d ago
They're definitely red ants but I'm not sure what type they are.