Midlothian,
United Kingdom 
Ants have cut my rhubarb leaves to shreds and are cultivating something that looks like black mud in my blackcurrant stems and under folded-over leaves. I can't find the nest(s). What can I do? -H (Edinburgh, Scotland)
24 Jun, 2010
Answers
Treat for aphids, which will get rid of the ants. More likely the damage to your rhubarb leaves is caused by slugs or snails or both.
24 Jun, 2010
Previous question
Well I wouldn't worry about the rhubarb leaves as they are toxic to humans. With regard to the black currants if you look closely you will probably find they are black fly and the ants are milking them. Spray with soapy water, or put on thick rubber gloves and rub off.
24 Jun, 2010