Any idea what this is. Thai neighbours told me it is very dangerous

It's one oof the varieties of Thai fire ants. They do inject a venom which can be painful and blister. Multiple bites can cause large...very large...pustules to form. My wife said she got bit just once years ago and it's a lot worse than a wasp sting. They are best avoided.

It's a row beetle. Do not touch.

http://en.wikipedia.org/wiki/Paederus

Thank you