The teenagers were caught at a hotel in Kenyan Nakuru in April. Around 5,000 ants were found in their room.
They are now fined equivalent to around 000 Swedish kronor, or one year's imprisonment for violating Kenya's nature protection laws.
The ants were intended for Europe and Asia, as part of a growing trend of smuggling less common species. Among the seized ants were thousands of Messor cephalotes, an unusually large, red ant species from East Africa.
The two other men – a Vietnamese and a Kenyan – were caught with "only" around 400 ants, but receive the same sentence as the Belgian teenagers.
