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  Social parasitism in ants is a very interesting  phenomena.

 There are 3 kinds:

1. temporary social parasites
2. permanent inquilines
3. slave-makers

 You can see more about it here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1689662/ (in English) and here http://ru.wikipedia.org/wiki/%D0%A1%D0%BE%D1%86%D0%B8%D0%B0%D0%BB%D1%8C%D0%BD%D1%8B%D0%B9_%D0%BF%D0%B0%D1%80%D0%B0%D0%B7%D0%B8%D1%82%D0%B8%D0%B7%D0%BC_%D1%83_%D0%BC%D1%83%D1%80%D0%B0%D0%B2%D1%8C%D1%91%D0%B2 (in Russian)