@SecondUniverse I've never heard of ants using spiky seeds like this. Many ants will cover the entrance with sticks and tree resin for antibacterial and defense purposes ... so it could be that. Is the plant the produces the seeds native? That is are the ants accustomed to encountering it? If it's not native they could be confused why they can't get them into the nest... Are they harvester ants? Do you have a closer photo of the ants?
S
