Tiger beetles, rice, Bangladesh

August 2017. Insects feeding in a rice field in Bangladesh. What are they?

They were identified as tiger beetles. They are predators so it would have been interesting to know what attracted them to the field.

There are similar aggregations in the plague soldier beetle Chauliognathus lugubris (Cantharidae) an unrelated beetle found in southeast Australia. The adults are nectar feeders, larvae are predators. The reasons for the aggregations are not yet known, but it is not associated with a particular food resource: https://blog.csiro.au/insect-of-the-week-the-plague-soldier-beetle-isnt-nearly-as-bad-as-it-sounds/.

Could it be a mating aggregation?