I saw these red insects in Taipei near XinBeitou MRT station in the last week of April 2017, around lunch time. They were fairly active and would keep checking each other out with their antennae for a moment and then move on to the next. What struck me was the wide range of sizes and development in the groups. I didn't notice any feeding or mating that I could recognize, just a lot of walking around and checking each other out.
There are plenty of birds around (this is quite a green area) but I didn't notice any interest by birds in eating them.
I've also included a screenshot from google maps so you can see the location and the trees growing in these concrete structures.
The body of the largest individual is probably 2.5 centimeters long.