There are quite a few red-and-black bugs in the area - like Paul already mentioned many in the Pyrrhocoridae, but I'm not 100% sure this is one. John Moore has a very similar, but also unidentified, specimen
on his thaibugs
site. From that image I would certainly say its a 5th instar nymph, but unsure of the family. Will search some more ...
P.S. I'm having half a mind toward Largidae, maybe some Physopelta sp.
, mostly because I can't seem to find good candidates with a red rimmed black pronotum in the Phyrrocoridae ... but that's more of a desperate guesstimation than that there would be any knowledge of Thai species involved
P.P.S. On review ... the very
long antennae seem to pose another problem
I'm afraid I'll have to leave it at that though ... no time to go on wild goose chase.