Ants don't do any harm to any plants. And even if they're pulling out the seeds, as you put it, what's the problem?

Many times, ants are an indicator that you have aphids on those plants. Aphids secrete a thick, sweet substance that ants love.

Nice, tj. Gardener, that Eryngium is a much favored nectar plant might be a clue to what the ants are so interested in. I'd guess that they find it easy to access the nectaries of the florets, perhaps dismantling them to do so.

Also, this is such a favorite nectar plant for so many different pollinators that you should never do anything to make the flowers less appealing to the ants lest you deter all of the others from a valuable food source.

Ants are not harmful to Sea Holly anymore then they are to Peonies and Sea Holly is one of the many plants that are not a particular favorite of Aphids. The Ants are there because of the abundant food Sea Holly provides to many insect species, pollen, nectar, and is a good addition to any insectary.

Thank you for the replies. I'm glad the ants aren't doing any harm to my plant.

I met a lady who sold me some perennial orchids and she said she has one sea holly for several years and she has never been able to collect seeds from it, so I thought maybe insects such as ants were either eating them or pulling them out before the seeds mature. I'm glad to hear that is not the case.

Mulchmama, The reason I want to collect some seeds is that it took me several years to find a place that sold sea holly and I rescued this one from the clearance section at Home Depot in a different city. So you can say this is my baby and I want to grow more:) I don't seem to have much success growing from store bought seeds.

TJ - All I can say is "Wow!" I hope my plant will spread like yours.

rhizo and kimmsr - Thank you for the info

Tsugajunkie -- I'm also in SE Wisconsin and have sea hollies, which returned this Spring against all odds! They've been doing beautifully, but now I see two of my plants appear to be covered with aphids. Have you run into this? I really don't want my gorgeous plants to be eaten alive if I can help it. Thanks!

Kaelie, this thread goes back to 2013.

While it does go back to 2013 a polite answer to Kaelie would have been nice.

The best method of control for Aphids is to use a sharp spry of water to knock the wee buggers off the plant. Some people use a hose while I prefer a spray bottle which gives me better control and is less apt to shred a plants leaves.

The sea holly looks great and prolific in the picture. I love the exotic looking flower. I bought one from the nursery last year but it died on me. What do I have to look out for to have it grown happily? I am thinking of starting from seed.