The Amazing Aussie Bee Amegilla (Asarapoda) dawsoni
Amegilla (Asarapoda) dawsoni, known by the common name of Dawson’s Bee, or Dawson’s Burrowing Bee, is one of the most incredible bee species in the world! This robust, large native bee hails from the Land Down Under - Australia. Like many creatures in Australia, this bee is quirky and charismatic. I had the pleasure of spending days observing and studying this fascinating bee species in August last year, which was one of the most incredible experiences of my life. Witnessing the emergence, mating, fighting, foraging and nesting activities is truly a sight to bee-hold. Standing in the rugged outback on a barren claypan, with large golden male bees zipping about me in pursuit of virgin females; pairs in copula scurrying across the claypan; jousts between males rolling about in the red dirt; and the sight of silvery females popping in and out of little clay turrets, is enthralling.
Dawson's bee occurs in North-Western Australia, and is known to be active only for a few months from late July to early September. Its activity is timed with the ephemeral rainfall in the Australian arid zone, which brings flushes of plants to bloom, including the bee’s foraging plants. The bees nest in claypans, including not just claypans in nature reserves, but on clay roads or claypans in a Pistol Range! Like the majority of native bees, and unlike the European honeybee Apis mellifera, A. dawsoni is a solitary species: each female builds her own nest, and forages to provision her offspring with nectar and pollen. Males play no role in parental care, but unlike the European honeybee, do not succumb to suicidal sex and continue to live after mating.
The nests of Dawson’s Bees are similar to many of its close relatives in the genus Amegilla, such as the blue banded bees and teddy bear bees. These are all solitary bees, but they nest gregariously, and up to 10,000 individuals may nest at the same site. An active nesting ground will be pock-marked with little nesting burrows.
The females dig through the hard-packed soil of the claypan, excavating nests up to 35 cm deep, using nectar to help moisten the clay. Burrows towards the end of completion have little cylindrical turrets up to 4 cm high constructed from the excavated soil and which prevent newly excavated soil from falling back in.
At the base of the main shaft, females excavate one to several urn-shaped brood cells, which they line with a waxy secretion. Brood cells are filled with food for the offspring – a watery mixture of nectar and pollen – then an egg is laid on top of the provisions, and the cell sealed with a circular mud cap. This is the end of parental duties; the grub-like larva hatches, feeds on the food provisions, and sheds its skin (moults) several times before pupating, metamorphosing and emerging as an adult bee the next year. The mature larvae become dormant for most of the year, timing their emergence for the following spring.
Newly 'hatched' adults must gnaw through the cell cap and chew their way up out of the nesting burrow. Males emerge prior to females (on average 15 days earlier) and avidly patrol the nesting ground, which then becomes the emergence and breeding ground. Males will often guard the entrance of emergence tunnels, waiting to pounce on a female as soon as she emerges. The female then scuttles across the claypan, the male piggy-backing on her, to a spot in the vegetation at the edge of the claypan where they will mate.
Like most bees, Dawson's bee is sexually dimorphic, which means the males and females can readily be distinguished. As in many other insects, but unlike most mammals, females are larger than the males. The females have a beautiful silvery furry thorax and head, and a burgundy abdomen, while males have a golden furry thorax and copper abdomen.
Dawson's bee is one of the largest bee species in Australia, dwarfing the introduced European honeybee, and is only exceeded in size by two species of Xylocopa (Koptortosoma), the great carpenter bees.
Interestingly, males are also dimorphic, with larger “major” males, and smaller “minor” males – an example of a conditional mating strategy. The major males fight on the breeding grounds for access and monopoly over newly emerged virgin females, while the minor males patrol the edges of the colony, mating with females that escape the mating battles on the claypan or sneaking a mating with foraging virgin females that evaded being mated at the emergence site. Minor males can often be seen zipping around forage plants, patrolling for visiting females. Males can detect virgin from mated females, which become unreceptive after mating due to changes in the female's pheromone profile.
For the major males, there is strong intrasexual selection on body size, which is tied to greater fighting ability, with the biggest baddest boys achieving the most matings: studies show that larger males are more likely to win battles and to be first to mount a sexually receptive virgin female, therefore achieving greater reproductive success. Competition for females at emergence sites can be intense. Major males will brawl with each other, sometimes fatally. Fights over a newly emerged female are especially fierce, and in some cases even the female is killed in the foray.
Unexpectedly, despite major males having the upper hand in battles over virgin females, they achieve only a minority of matings, and minor males comprise 60-80% of the population. One explanation for this is that minor males have longer lifespans: the major males are more likely to die early from their battles, and being larger and more visible are also more likely to be eaten by predators such as crows.
Although Dawson's bees forage on a range of plant species that are not closely related to each other, they are nevertheless quite restrictive in what they will forage on. Males and females both forage for nectar, but only females forage for pollen, which provides the protein, fats and minerals they need to produce eggs and as food provisions for their offspring. Pollen seems to be sourced from only four plant genera: Senna (Caesalpiniaceae), Eremophila (Myoporaceae), Solanum (Solanaceae) and Trichodesma (Boraginaceae).
However, recent observations by Dr Stephen Buchmann and I have shown that the vast majority of foraging, including by females, is for nectar. The preferred nectar source is Trichodesma zeylanicum – on a patch of these flowers hundreds of bees can be observed buzzing about and nectaring. When this plant is absent however, we made a new observation that both sexes will forage for nectar on Scaevola spinescens (Goodeniaceae).
Amegilla dawsoni belongs to one of the few genera of bees in Australia with a well-resolved taxonomy, thanks to recent taxonomic work that has resulted in up-to-date revisions of not only the Asarapoda subgenus to which A. dawsoni belongs, but the other two subgenera of Amegilla in Australia, Notomegilla and Zonamegilla.
Unfortunately, up-to-date revisions have not been done for many other native bee genera in Australia, and taxonomists estimate that around 1000 native bee species remain undiscovered and un-named. Taxonomy Australia's mission is to achieve a similar level of resolution for all bees as has been achieved for Amegilla!
Perhaps the biggest impediment for taxonomy of Amegilla at present is the use of common names. Some of the most commonly encountered Amegilla bees are called 'teddy bear bees' or 'blue banded bees', but these names are shared by multiple species, belying the diversity of the wonderful genus Amegilla.
Abuzz About Dawson's Burrowing Bee
A book on Kit’s adventures to discover this bee is also available: "Abuzz About Dawson's Burrowing Bee : a travel log by the Bee Babette, about her quest to find Amegilla (Asarapoda) dawsoni" is a book filled with the musings, observations, and fascinating factoids of a scientist on her road trip to see the world's most wonderful and wicked of bees. In this 80+ page book you'll be amazed by the beauty of these big beautiful bees, with high quality photographs featured throughout. All proceeds will be towards funding the research, time, fuel and travel costs that were involved in this self-funded venture.
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A version of this article first appeared in 2 Million Blossoms.