Fungus-growing ants are a remarkable taxon of New World ants that engage in a mutualistic symbiosis with basidiomycete fungi. Their fungus-gardens are valuable resources and are exploited in countless ways by parasites and other beneficiaries outside of the ant-fungi mutualism. Here, for the first time, we report on the agro-predatory behavior of the ant Megalomyrmex incisus on Mycetophylax conformis and Mycetophylax morschi fungus-growers from sand dunes near Ilhéus, Brazil. Me. incisus workers raided colonies of My. conformis and My. morschi and aggressively antennated, pulled, bit, and stung the fungus-growers, which played dead or retreated on the fungus. Me. incisus quickly usurped the fungus-garden and expelled all Mycetophylax workers. The usurpation closely resembled that described for raids of Me. wettereri on Cyphomyrmex longiscapus, in that the fungus-growers remained passive and avoided confrontation. This passive behavior suggests that Me. incisus uses chemical weapons that facilitate the exploitation of the host colony resources.