I have never tried them as they are quite costly. I could do with one for snails though - I have a plague of them!

However if you want to give it a go Marshalls sells nematodes for ants - if you copy and paste the link into your browser it will hopefully come up :

http://www.marshalls-seeds.co.uk/nemasys-ant-killer-no-ants-ant-killing-nematodes-pid2590.html?gclid=CPL87e_4nKICFRyX2Aodfhx4ww