6530. Size 2-3 mm. Month July. Season Summer. Weather conditions: Hot & sunny. Outdoors. I have no idea what the bugs are that these ants are so interested in, nor why they have colonized the plant. I have not been able to ID them through Google. Calgary, AB. Canada

Number 6530.  Those are aphids (Hemiptera/Sternorrhyncha: Aphididae), aka ‘plant lice.’ They feed on sap from plants, and as they feed, they excrete excess fluid in the form of ‘honeydew’ which some species of ants find very attractive. Click here for more detailed information.