The ants are a non issue to the tree and probably more of a benefit than
anything else. With the coconut palm the trouble may be more where you
are trying to grow it. Not sure of elsewhere in the country but in
Florida I don't think I have seen them happily grow much further North
than Port Charlotte for example.

I think there is actually a town called Florida in South Africa but I
don't live anywhere near it :-) I have a couple of other palms in the
yard and they all do just fine - the one is probably almost three
stories high! Also, there is a healthy-looking fan palm about three
metres (yards) closer to the house.

I suspected the dreary look may have been caused by the insects because:
1. They seemed to be the only variable from the successful palms in the
yard.
2. They live on plant material (or don't they?)
3. I don't particularly like ants, so they seem to be a good scapegoat :-)

Are there any other good reasons why the tree would suffer? Perhaps it
is just in need of some fertilizer?