Common names: oil-collecting bee, oil-bee (Eng.).
Derivation of scientific name: This species of Rediviva was named after the late Charles M. Michener, the world’s leading expert on bees, in recognition of his significant contribution to our understanding of South African bees and more specifically for his taxonomic revision of the bee family Melittidae.
You may know that bees collect pollen and nectar, but did you know that some bees also collect floral oils? Such bees have evolved specialised tools for gathering, transporting and using floral oils. And perhaps most notably, several oil-collecting bees have evolved extremely long forelegs, some reaching twice as long as their body length. The female bees use their elongated forelegs to reach the oils deep inside the floral spurs of their host flowers.
The front part of the female’s forelegs – the tarsi – are equipped with specialised hairs to mop up the floral oils. It is no wonder that this charismatic group of bees represent one of the world’s most striking examples of pollinator adaptation.
Description/How to recognise the species
These slender bees are distinctive because the females have extremely long forelegs (15–18 mm long) that can measure one and a half times the length of the bee’s body. The body size of oil-collecting bees is similar to that of a honeybee. The bee’s body is covered in pale white to straw-coloured hairs becoming darker towards the tip of the abdomen. The segments of the foreleg furthest from the body – the tarsi – are covered in orange hairs, which are specialised oil-collecting hairs. The dense plumose hairs on the hindlegs (scopa) allows oil-collecting bees to carry both floral oil and pollen back to the nest. At the tip of the abdomen is the sting. Only females can sting.
Getting around
Bees have two pairs of wings on either side of their body. Bees fly from their nest in search of host flowers, and will fly from flower to flower, and back to their nest. The foraging distance for most solitary bees is less than 500 m and rarely exceeds 1 km per foraging trip.
Distribution
This indigenous bee species is only found in the southwestern part of the Western Cape, in the areas surrounding the Piketberg, southwards to Malmesbury and northwards to Citrusdal and Clanwilliam.
Habitat
The oil-collecting bee is found in remnant patches of fynbos and renosterveld, such as on road verges, and in two small nature reserves. It emerges during the spring months of August and September to coincide with flowering of their host plants (e.g., Diascia longicornis).
Oil-collecting bees are solitary bees that nest in the ground. This means that a single female bee will dig a below-ground nest, which she provisions with pollen, and possibly oil as well, and then lays her eggs.
Food
All species of oil-collecting Rediviva bees have narrow host plant associations and have been recorded to collect floral oils from four plant families: Iridaceae, Orchidaceae, Scrophulariaceae and Stilbaceae. Rediviva micheneri has only been recorded to collect floral oils from eight species of Diascia (Scrophulariaceae), with most bees observed foraging on the long-spurred D. longicornis (spur length ranging from 4 to 18 mm). Given that these oil-secreting host plants do not produce nectar, the female bees collect nectar from species of Morea (Iridaceae) and Oxalis (Oxalidaceae). Nectar is an important source of carbohydrates in the form of sugars, as well as proteins in the form of amino acids. Bees use their tongues (proboscis) to suck or lap-up nectar. Pollen plants used by this species have not been recorded. Pollen is the main source of protein for female bees to provision their nests and feed their larva.
Sex and life cycles
Very little is known about the nesting biology of Rediviva, and our knowledge is limited to one species Rediviva intermixta. A broad account is given here:
Sex
Adult bees are active for 6–8 weeks during the spring months. Male bees typical emerge before females. They will wait close to the nesting site or patrol host flowers nearby for females to emerge. When the females do emerge, several males mob the entrance and tussle with each other (forming mating balls) hoping to be the first to mate with her.
Family life
Female solitary bees are solely responsible for construction and provisioning of their nests. A female bee must ensure that she has provided sufficient resources (e.g., pollen) in the brood cell for the offspring (larvae) to complete their development once the cell has been closed-up. The female has no further contract with her developing brood after this.
To ensure her offspring and its food provision are protected from pathogens, parasites and predators, especially when nesting below-ground, the female oil-bee carefully lines the nest cell using floral oil prior to provisioning the cell. The typical developmental cycle for a bee is to move from egg to larva to pupa before emerging as an adult.
THE BIG PICTURE
Friends and foes
Bees are important pollinators of wild plants and agricultural crops, and in the case of oil-collecting bees, can be the sole pollinator for several endemic plant species. Bees are important food for birds, spiders, and insects such as robber flies.
Smart Strategies
Oil-collecting bees have evolved elongated forelegs to reach deep into the spurs of oil-secreting flowers, blade-like hairs for perforating the oil glands and modified hairs for absorbing the oils. The female oil-bee uses the floral oils as a lining for brood cells and possibly as larval food.
Poorer world without me
This oil-collecting bee species is an important specialist pollinator for several endemic oil-secreting plant species (Diascia spp.) in the family Scrophulariaceae.
Conservation status and what the future holds
The conservation status of this bee species has not yet been determined. Wheat is extensively cultivated in the area in which these bees predominantly occur. Consequently, 90% of their plant habitat is classed as threatened. Currently there are no direct protection measures in place for this species, although some protection is afforded by two nature reserves that overlap with the southern part of its range.
Relatives
There are 33 described species of Rediviva in South Africa of which 26 species are oil-collecting bees. South Africa is a centre of diversity for Melittidae particularly in the arid areas. The Melittidae is an ancient bee family and well represented in the fossil record dating back to the Eocene (approximately 53 million years ago). Molecular data places Melittidae as the basal bee family, the sister to all other six bee families.
Scientific name and classification:
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Melittidae
Genus: Rediviva
Species: R. micheneri Whitehead & Steiner, 2001.
References and further reading
- Whitehead, V.B. & Steiner, K.E. 2001. Oil-collecting bees of the winter rainfall area of South Africa (Melittidae, Rediviva). Annals of the South African Museum 108: 212–219.
- Melin, A. & Colville, J.F. 2020. A nesting aggregation of Rediviva intermixta (Melittinae: Melittidae) with males sleeping together in burrows: Namaqualand, South Africa. Journal of the Kansas Entomological Society. 92: 561–568.
- Danforth, B.N., Minckley, R.L. & Neff, J.L. 2019. The solitary bees. Biology, evolution, conservation. Princeton University Press.
- Michener, C.D. 2007. The bees of the world. The Johns Hopkins University Press.
Author: Annalie Melin
E-mail: annalie.melin@gmail.com