At least 85 people were hospitalised while others were given first aid following the incident at the foot of the 180-metre (600-foot) fortress of Sigiriya.
The Sigiriya rock, 160 kilometres (100 miles) north of Colombo, is a World Heritage site known for frescoes of bare-chested women.
Hundreds of thousands of tourists come to see the frescoes but are told to maintain silence so as not to upset the wasps.
The authorities do not use chemicals or smoke on the insects, fearing they could harm the 1,500-year-old frescoes known as the Sigiriya maidens.
Military personnel were deployed to help evacuate the visitors Monday and rush them to hospitals.
Police said there were no foreigners among those hospitalised.
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