Tachinid Fly (Leschenaultia spp. ) sipping nectar
At our 2016 Butterfly Encounter, we observed many large, black flies visiting flowers. Their flight and behavior is similar to bumblebees and they are easily mistaken. They are Tachinid flies in the Genus Leschenaultia. They are parasitoids of caterpillars and are important regulators of caterpillar populations. This fly must have had a large caterpillar host to reach its large size.
Source: Living With Insects Blog