Aculeata Agonistes: Yellow-faced Bees (Hylaeus)

Hylaeus is a large genus (~900 species) of mostly very small bees (5-6 mm long is common) in the family Colletidae. They are worldwide in distribution and especially diverse in temperate to subtropical Australia. Hylaeus also do reasonably well in the temperate to boreal areas of North America (55 species north of Mexico). Tatiana Romankova of the Royal Ontario Museum estimated that at least 13 species of Hylaeus occur in Ontario (Romankova 2007) and 7 of these species may also occur in Alberta. She provides a key to the species in Ontario, but I’m not sure how useful it would be here, since we probably also have species not represented in the East.

Most Hylaeus nest in cavities such as hollow stems, beetle galleries, or nail holes in wood. So, planting shrubs with hollow stems or making drilled-bee homes should help to attract them to your yard. Some species have more specific nesting sites such as empty plant galls or the cavities in volcanic rock (Michener 2007). The latter habit is probably useful in Hawaii where Hylaeus is the only genus of native bees. Sixty different species are known in the Hawaiian Islands today and they appear to have arisen from the successful colonization of the Island of Hawaii by one species (probably from Japan or another part of eastern Asia) about a half million years ago (Magnacca & Danforth 2006).

Hylaeus are very unusual bees. They have few of the branched body hairs that are the definitive character that separates bees from their close relatives the hunting wasps. They also lack the specialized tufts of hairs (scopa) or leg basket (corbicula) that other bees use to collect pollen. In fact, they are so wasp-like that one species has been used to fool entomologists on a Monday Night Mystery at the Myrmecos Blog. Bees are just a branch of the hunting wasp lineage and so the ur-bee must have been rather waspish.

Are Hylaeus, then, among the most primitive bees? Not according to a recent molecular phylogeny of the Colletidae (Almeida & Danforth 2009). Instead, Hylaeus species appear to be relatively recently derived within the Colletidae and their particularly un-bee-like appearance and habits are relatively recent evolutionary innovations. This includes behaviours such as ingesting both pollen and nectar that they carry in their crop and use to provision their nests with the liquid mixture. This is very similar to what Pollen Wasps (relatives of the yellow jackets: Vespidae, Masarinae) do, but both cases seem to be parallel derived behaviours and not vestiges of the proto-bee.

Hylaeus species are known to visit a variety of flowers for nectar, and since the pollen is not easily collected out of the bees, it had been assumed that the bees are pollen generalists as well. However, Virginia Scott (1997) studied three species of Hylaeus in Michigan and found that all were specialized on pollen from members of the rose family (Rosaceae). The hard outer coating of pollen survives digestion and Dr Scott had the fun job of collecting Hylaeus larval fecal pellets, making slide mounts, and identifying the pollen. Much of scientific research consists of equally fun jobs, but I hope Dr Scott developed an appreciation for the wonderful form of pollen grains. In any case, hers is the only good study on the pollen habits of Hylaeus that I could find. At her study site cinquefoils (Potentilla), blackberry and its relatives (Rubus), and meadowsweets (Spiraea) were the preferred foods.

The Home Bug Garden has many Rosaceae, including representatives of all three genera, at least in the old sense of Spiraea which included goatsbeards (Aruncus) and Queen-of-the-prairie (Filipendula). We also have many bushes with hollow stems, holes drilled into logs and boards, and are graced by some of The BugWhisperer’s experimental bee hotels. Perhaps all of these have come together in this rather dreary summer to make the Home Bug Garden a good habitat for Hylaeus.

References:

Almeida EAB & Danforth BN. 2009. Phylogeny of colletid bees (Hymenoptera: Colletidae) inferred from four nuclear genes. Molecular Phylogenetics & Evolution 50: 290–309.

Magnacca KN & Danforth BN. 2006. Evolution and biogeography of native Hawaiian Hylaeus bees (Hymenoptera: Colletidae). Cladistics 22: 393–411

Michener CD. 2007. The Bees of the World, 2nd Ed. The John Hopkins University

Press.

Romankova TG. 2007. Bees of the genus Hylaeus of Ontario (Hymenoptera: Apoidea: Colletidae). J. ent. Soc. Ont. 138: 137–154.

Scott V. 1997. Pollen selection by three species of Hylaeus in Michgan. Journal of the Kansas Entomological Society suppl. (1996): 195-200.