"Robert E A Harvey" wrote in message
............. this morning. Saucer sized. Turned the lawn brown.
[...]

I've got 2 or 3, thought it might be the dogs but no previous
preoblems there. On investigating it is ants.

Sometimes brown patches in lawns could be caused by chafer grubs.
http://www.bbc.co.uk/gardening/advic...l?chafer_grubs

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Sue