This also surprised me a bit. A recent (2014) paper states:he eusocial ants (and others) have genetic castes and specializations. Apis does not.
From: The role of chromatin and epigenetics in the polyphenisms of ant castes. Briefings in Functional Genomics. Advance Access published January 24, 2014Although ant species exist for which complete genetic caste determination has been described, these seem to be the exception rather than the rule