Australian Native Bee Library
Ctenocolletes smaragdinus
Ctenocolletes smaragdinus is a spectacularly beautiful bee, with a shiny metallic green body.
It is a species in the family Stenotritidae, a family of bees endemic to Australia – found nowhere else in the world.
The Stenotritidae are an unusual family – they are the most species-poor of all of the seven bee families in the world, with just 22 described species. There is no doubt more species to be described as the most recent was described in 2025.
All stenotritids share the common features of being large, 12–18 mm, robust-bodied, hairy, with short-tongues. They were once thought to be a subfamily of the Colletidae, but both genetic and morphological evidence indicates they are distinctive.
Ctenocolletes smaragdinus is the only metallic bee in this family, the rest are hairy and often striped. The stinger of the female stenotritids has become vestigial during evolution meaning it has been reduced and no longer functions.
Taxonomy
Ctenocolletes smaragdinus
Family
Stenotritidae
Genus
Ctenocolletes – 10
Stenotritus – 12
Species
smaragdinus
Distribution
Stenotritidae occur throughout mainland Australia but are found mainly in Western Australia. Ctenocolletes smaragdinus are present in inland southwest Western Australia.
Habitat
Ctenocolletes smaragdinus is restricted to native vegetated habitat. This is true of all stenotritids.
Floral preferences
Ctenocolletes smaragdinus forages for pollen from plants in the family Myrtaceae. Host genera include Baekea, Beaufortia, Leptospermum, Melaleuca, and Verticordia.
Role in pollination
The actual role of stenotritids as pollinators has not been investigated. However, as large, fast-flying bees that fly from one plant to anotherand featuring dense hairs and developed scopae, pollen-collecting hairs of the female, it can be assumed that they are important pollinators of the native wildflowers that they visit.
Sociality
All Stenotritidae, including C. smaragdinus are solitary, meaning each female digs and uses a nest of her own. Females will, however, often nest close by in nesting aggregations, and are attracted to nest in soils that have previously been inhabited.
Nesting
Stenotritids are ground-nesting bees. Nests of Ctenocolletes all lack tumuli, known as mounds of earth around the burrow entrance. Although the nest architecture of C. smaragdinus has not been studied, nests of other Ctenocolletes, C. albomarginatus and C. nicholsoni, are deep – more than 3m.
C. smaragdinus builds inconspicuous nests in gently sloping, sparsely vegetated sandy soils. Their nests can be quite
deep: excavations of nests have recorded cells in burrows almost 2m deep.
Wasps in the family Gasteruptiidae have been observed to enter Ctenocolletes smaragdinus nests. These wasps are predator-inquilines meaning they live in the nest of the host and consume both the host’s offspring and their food stores.
Life cycle
All bees they start as an egg, hatch as a larvae, pupate and metamorphose to emerge as an adult bee. Unlike most bees, they don’t spin cocoons. They appear to mainly emerge in September, with peak activity occurring in October.
Some males exhibit territoriality, staking out a good patch of flowers and hovering near them, waiting for a female.
Copulation can last a while and once a male mounts a female, she will often continue to fly with him piggybacking her, even resuming foraging, with both partners beating their wings, the male taking cues from the female.
As one can imagine, unlike the characteristic fast flights of stenotritids when unpaired, flight of conjugate pairs is laborious.
Conservation status
Like 99 per cent of Australia’s native bees, no stenotritid species has had their conservation status assessed. However, it is highly likely that at least some species could be listed as in need of conservation attention and could be threatened with extinction.
They are entirely reliant on intact, native vegetation, suitable ground for nesting and the specific wildflowers they forage on.
Threats
Known threats include:
- Livestock trampling and compacting soil.
- Impervious surfaces such as concrete and tarmac overlaying bare ground.
- Loss of foraging resources due to agriculture practices.
- Competition for nectar and pollen resources from the European honey bee.
- Climate change: climate change can threaten bees in numerous ways, including wildflowers, disrupting the flowering times of host plants, altering nectar and pollen chemistry, and placing heat stress on bees. Large-bodied bees are considered to be more vulnerable to climate change.
Fun Facts
Commensal acarid mites are associated with some Ctenocolletes.
The mites, are associated with the bees throughout their entire lifecycle, and their complete breeding cycle occurs in the hosts’ sealed brood cells – the cells in which the larvae are developing with the nectar and pollen provisions. They cause the host bees no harm, and this is likely a mutualistic relationship where the bees benefit from sanitary services.
While males are aggressive to each other during the day, they will bunker down together at night and have been observed appearing to sleep in aggregations on a Casuarina shrubs, returning to their sleeping location each night.
With written contribution from Kit Prendergast