Amegilla dawsoni

Tilcayo Cats original · Amegilla · Sources and editorial assessment · Originals retention rule

Amegilla dawsoni, or Dawson's burrowing bee, is a large solitary bee of Western Australia. Females excavate nests in hard clay, sometimes gathering in very large nesting aggregations. The males occur in two size classes with different ways of finding mates, making the species an extensively studied example of variation within a bee population.

Appearance and classification

The species belongs to Asaropoda, a group within Amegilla. Rayment described it in 1951; the name-bearing male was collected at Onslow. In the 2020 Australian revision, it is the largest Asaropoda species treated. Females have white hair on the head and thorax, whereas males have light brown hair. The female's hind-leg pollen brush is black.

Large males are approximately female-sized, while small males are about three-quarters as long. The division is not simply the usual difference between males and females: both large and small forms are male.

Feature	Females	Males
Head and thoracic hair	White	Light brown
Size pattern	Larger than the small male form	Two distinct size classes
Nest work	Excavate and provision their own nests	Do not construct or provision nests

The colour and size comparison follows the taxonomic revision; the nesting distinction is described by the Western Australian Museum.

Distribution and annual cycle

The bee inhabits north-western Western Australian plains, extending south towards Paynes Find. The museum gives July to September as the adult season. Much of the remaining year is spent as dormant young inside underground cells. Closely packed nests do not form a honeybee-like communal colony: each nesting female provisions her own offspring.

Building a nest

Females soften hard clay with nectar before biting away the soil. Excavated material forms a turret around the entrance. A shaft leads to brood cells roughly 15–30 cm below the surface. Each cell receives pollen and nectar, followed by an egg, and is sealed before the female constructs another. Development and the resting period take place underground; the new adult eventually digs out.

Flowers and food

The 2020 revision records the bee on plants including Stemodia grossa, several Eremophila species, Trichodesma and Acacia. These records are consistent with the importance of flowering conditions during the relatively short adult season, but do not quantify the bee's contribution to pollination across its range.

Why are there two kinds of male?

Large males compete for newly emerging females at nesting sites. Small males more often search around nearby flowers. The revision reviews several attempts to explain why mothers produce both forms. Work on brood provisioning found a tendency for small sons to be produced later in the nesting season, when floral resources were declining. The authors nevertheless regarded the broader explanation of the size difference as incompletely resolved.

A study of emergence timing found that males usually appeared before females, and that small males tended to appear before large ones, both across the season and within a day. Earlier arrival was proposed as a possible advantage for males that would be disadvantaged in contests with larger rivals; that interpretation remains a hypothesis about the pattern.

Genetic work has also tested the breeding system and the allocation of offspring within nests. One study found evidence that a nesting female was the mother of all the offspring in her nest, with brood parasitism unlikely in the sampled nests. This is evidence about the nests examined, rather than a claim that an exception could never occur.