This is a subspecies of the Malaysian mainland Euploea midamus chloe (Blue Spotted Crow), which is found on Singapore Island and on Pulau Tioman. The subspecies singapura lacks the blue sheen of the mainland species. At a glance, the Singaporean subspecies resemble Euploea crameri bremeri (Spotted Black Crow) very closely. The only difference is that in this species, there are 3 elongated white spots at the apex of the forewing, as compared to Euploea crameri bremeri's 4 spots. This is not easy to distinguish when the two species are in flight.
The caterpillar of this species is believed to feed on Strophanthus, Roupellia and Nerium. The Singapore subspecies of the Blue Spotted Crow is not common and is rarely seen, except at the occasional flowering tree. However, it has also been observed outside the nature reserves in suburban housing estates in Singapore.

See Butterflycircle blog article - Life History of the Blue Spotted Crow