The genus Amegilla (currently classified under family Apidae, subfamily Apinae, tribe Anthoporini) are small to medium-sized, robust bees, common throughout the Asia-Pacific region from China all the way to Australia. There are many different species in this genus, but one group worth mentioning are the blue-banded bees, so called because their abdomens are striped with brilliant blue or blue-green on black. There are several similar species in different localities throughout the region; two different species, Amegilla calceifera and Amegilla zonata, are probably present in Hong Kong. I have not examined specimens from Singapore in detail yet; there is at least one species which is larger with more turquise or metallic green bands when compared to those from Hong Kong.
They range from around 9 mm to 14 mm in body length. They are mainly dark brown, grey or black, often with yellowish or orange-brown hairs covering the thorax. The black abdomen generally has four or five blue bands. Although the bee is small and usually fast-flying, these bands can be easily noticed.
These bees are quite common throughout much of their range, and can even be found in urban areas. They are frequently seen at flowers, collecting nectar and pollen. They have a unique way of collecting pollen; they cling to the flower and buzz sharply, causing the pollen to be displaced by the vibration and sticking to them. (Besides these bees, only the bumblebees and possibly the large carpenter bees are capable of doing this). Their long tongues can also reach into deep flowers. They are important pollinators of many different plants, including some tropical fruit such as rambutan (personal observation; a rambutan tree outside a friend's house in Singapore was visited mainly by blue-banded bees a couple of weeks before the tree started fruiting). They fly fast and frequently hover, pausing before entering a flower.
Blue-banded bees nest in or near the ground. In the wild, they like natural slopes with soft but firm soil, and frequently nest in clayey soil. The nest is a small hole, barely 3 to 5mm in diameter, built at a concealed angle in such surfaces. In more urban areas, they like to nest in soft, aged mortar between bricks, weak cement and other such surfaces. They also nest in flowerbeds and on turf
These bees pose virtually no threat to people. A sting from these bees feels like a mere pinprick and is extremely unlikely anyway. A neatly kept garden and well-maintained walls and brickwork will discourage them from nesting where people may contact them. It should be noted, however, that they should indeed be encouraged in gardens.