The secret lives of blue banksia bees

Often when people think of bees they picture fairly hairy little insects buzzing from flower to flower. But not all of Australia’s 1650+ currently-known bee species are buzzing balls of fluff. We have many bee species that are largely hairless. Despite their baldness, these bees are just as interesting as their lavishly haired relatives.

One group in particular, the hylaeine bees in the family Colletidae, has some very charismatic species. There are a little over 200 described hylaeine species, and new species continue to be discovered. Telling some of these species apart from one another can be a challenge though, because for about half of them, taxonomic keys simply do not exist. Hylaeine bees are often given the general name of ‘masked bees’ because of the pale markings that are present on the faces of most species. They're relatively hairless, wasp-like bees that range in size from tiny 3 mm long species to large 14 mm species.

One of the biggest, at 12 mm long, is Hylaeus alcyoneus. Found in coastal areas of southern Australia, these rotund bees are commonly called ‘blue banksia bees’ because of their dark metallic-blue abdomens and their particular fondness for visiting banksia flowers. Like most of Australia’s native bees, H. alcyoneus is a solitary bee, and in this case the females nest by themselves in pre-existing holes in wood, such as beetle holes in dead branches or trunks of trees. Inside these cavities females construct a series of small brood cells, within each of which a single egg will be laid. These brood cells are encapsulated in a waterproof, cellophane-like material which the female secretes from her mouth.

A H. alcyoneus female, with her brilliant blue abdomen. Photo: James Dorey©

To collect pollen and nectar to feed their young, female H. alcyoneus mainly visit banksia inflorescences. Unlike most bees, H. alcyoneus and other hylaeine bees do not carry their collected pollen on the outside of their bodies, they instead swallow it to carry it back to the nest. In the bee’s stomach the pollen mixes with the nectar she also swallows, and back at the nest the female regurgitates this sweet and proteinaceous mix for her offspring to consume. This is rather like a seabird returning to her nest with a stomach full of fish to feed her chick.

A H. alcyoneus female 'bubbles' to concentrate the mix of banksia nectar and pollen from her stomach, before returning to her nest. Photo: Tobias Smith©

It is at banksia flowers that H. alcyoneus females encounter the males. Individual male H. alcyoneus establish territories around a banksia inflorescence, competing with other males for the best positions. Males will threaten each other and occasionally physically wrestle to try to dominate the best territories. For this purpose, the males, which are larger than the females, have an impressive pair of spines on the underside of their abdomen, which are violently struck against their opponents using abdominal thrusts. Dominant males choose the most attractive inflorescences, with fresh, open flowers, and wait attentively to try to mate with any females who come in search of pollen and nectar.

After braving the males and filling up on pollen and nectar from banksia flowers, females will often perch on stems or leaves nearby and repetitively regurgitate and swallow the sticky contents of their stomach, in a process commonly referred to as 'bubbling'. They do this to concentrate and thicken the liquid meal before returning to the nest to provision their offspring with it.

Blue banksia bees are perhaps one of Australia’s most impressive bees, so if the weather is warm and the banksias are in flower, get outside and do a bit of bee spotting. If you are lucky, and patient, you might see both the females and males doing their thing.

© Tobias Smith 2020