My students want to do some breeding experiments for waste treatment. We are from the Philippines. Hermetia illucens should occur in the country, but I have no idea how common it is in nature.
Black soldier flies spend the most part of their live in larva state and only something like 2-3 days as a flie. So you can easily find it in compost or in decomposing organic matter as larva.
Nevertheless these flies spread theirself quickly and it could envade your country if they didn't already. For example I use to make compost In Lyon, France. This Flies were introduce in south of France, 300km from Lyon, 2 years later these flies were in all compost in Lyon.
Hi Dr. Hendrik! We collect stratiomyid larvae by placing manure as bait. We use guinea pig droppings since we are rearing them, maybe excreta from other animals will also do. Some literature also use dampened fish feeds or other decaying material.
If you plan to collect the adults, maybe you can try an ovitrap with a manure/feeds bait placed inside a cage with an inverted cone as entrance. I hope this helps. All the best!