Hylaeus is a large (over 500 species) and diverse cosmopolitan genus within the bee family Colletidae. This genus is also known as the yellow-faced bees or masked bees. This genus is the only truly globally distributed colletid, occurring on all continents except Antarctica.
Description The genus of bees consists of generally small, black-and-yellow or black-and-white wasp-like species. The resemblance to wasps is enhanced by the absence of a scopa, which is atypical among bees. The body form of this genus is described as hylaeiform (slender); the hairs inconspicuous without magnification; and scopa inconspicuous or absent.
Males have an intermediate glossal shape with a small to distinct median apical glossal point.
Hylaeus carry pollen in the crop, rather than externally, and regurgitate it into the cell where it will be used as larval food. Like most colletids, the liquid provisions are sealed inside a membranous cellophane-like cell lining.
Nests are typically made in dead twigs or plant stems, or other similarly small natural cavities, rather than constructing or excavating their own nests as in many other bees.
Some species of Hylaeus have been associated with strong scents. In particular, European species such as Hylaeus prosopis are characterised by having a strong "lemon-like" scent. Further investigation has attributed this scent to a substance generated by the mandibular glands of both males and females, composed of neral and geranial. It is believed this substance is used as a defensive secretion and/or a social pheromone.
Species
Some selected species of Hylaeus are: Hylaeus agilis Hylaeus alcyoneus - banksia bee Hylaeus anthracinus – anthricinan yellow-faced bee Hylaeus assimulans – assimulans yellow-faced bee Hylaeus facilis – easy yellow-faced bee Hylaeus hilaris – hilaris yellow-faced bee Hylaeus kuakea Hylaeus longiceps - longheaded yellow-faced bee Hylaeus mana Hylaeus nigritus - black-masked bee Hylaeus sanguinipictus
For the full list, see: List of Hylaeus species
Subgenera At least 44 subgenera of Hylaeus are known. These have been categorised geographically as follows by Ikudome (1989):
Australasian Region (19 subgenera): Analastoroides, Edriohylaeus, Euprosopellus, Euprosopis, Euprosopoides, Gnathoprosopis, Gnathoprosopoides, Hylaeorhiza, Hylaeteron, Laccohylaeus, Macrohylaeus, Meghylaeus, Planihylaeus, Prosopisteroides, Prosopisteron, Pseudhylaeus, Rhodohylaeus, Spearhylaeus and Xenohylaeus. Palearctic Region (12 subgenera): Abrupta, Dentigera, Hylaeus, Koptogaster, Lambdopsis, Mehelyana, Nesohylaeus, Nesoprosopis, Paraprosopis, Patagiata, Prosopis and Spatulariella. Nearctic Region (7 subgenera): Cephalylaeus, Hylaeana, Hylaeus, Metziella, Paraprosopis, Prosopella and Prosopis. Holarctic Region (3 subgenera): Hylaeus, Paraprosopis and Prosopis. Oriental Region (5 subgenera): Gnathlaeus, Hoploprosopis, Nesoprosopis, Nesylaeus and Paraprosopis. Ethiopian Region (4 subgenera): Alfkenylaeus, Cornylaeus, Deranchylaeus and Metylaeus. Neotropical Region (4 subgenera): Gongyloprosopis, Hylaeana, Hylaeopsis and Prosopis.
Distribution and status A significant diversity of Hylaeus is found in Hawaii — approximately 64 species are recorded as living there. Hylaeus are the only bees considered native to the islands and most of those are unique to the island chain; the diversity of this genus is far greater in Hawaii than in all of mainland North America. Many of them are species of concern, and some recorded there are possibly extinct. For example, H. finitimus was last collected 100 years ago, and only ever seen on the island of Kauaʻi.
The Hawaiian bee population and diversity is somewhat fluid — within the past ten to twenty years several Hylaeus species have been found and identified on the islands as new to science. In October 2016, seven species were officially listed as endangered by U. S. Fish & Wildlife, the first bees to ever be placed on the endangered species list.
North America Canada There are 20 recorded species of Hylaeus in Canada, and an estimated 30 different species based on DNA barcoding. There are multiple reasons that extra species may not currently be recorded: colour markings and variations have been traditional identifiers leading to multiple junior synonyms, this genus is easily established outside of its native range, and heteroplasmy is known in some Hylaeus species which can lead to difficulties with specimen identification.
USA
There are currently an estimated 130 species of Hylaeus in the USA.
Several species have been accidentally introduced to the USA. This includes: Hylaeus leptocephalus found throughout the country; Hylaeus hyalinatus found in urban New York, New Jersey and Pennsylvania; Hylaeus punctatus found in central California, Mid-Atlantic states, the Chicago region and Denver area; and Hylaeus (Prosopis) variegates in the greater New York city region.
One masked bee of interest in the country is Hylaeus lunicraterius. This bee is only recorded at the Craters of the Moon National Monument, Idaho. Little is known about its biology, however it is believed to nest in the crevices and holes in the lava flows.
Oceania Hawaiian Islands
A single clade of 64 known Hylaeus spp. are native to Hawaii.
Phylogenetic evidence suggests that the first Hylaeus species arrived on the island of Hawaiʻi between 0.5 and 0.4 million years ago. From here, it is believed that descendants of the initial (presumed ground-nesting) colonist separated in order to specialize in the different ecological niches available. This included coastal and dry forest strands (H. longiceps and H. anthracinus); mid-elevation and montane dry shrubland strands (H. difficilis); cleptoparasite strands (H. inquilina); and wet and mesic forest wood-nesters. After this divergence, it is believed dispersal to other Hawaiian Islands occurred.
It is likely that the rapid speciation of Hylaeus occurred due to open expansion into open niches in novel habitat. Using an equation (r=lnN/t) developed by other studies into the evolution of Hawaiian groups, it can be calculated that the minimum speciation rate for Hylaeus on the island of Hawaiʻi is 9.23 species per million years.
In terms of nesting biology, those that inhabit wet areas nest in stems or wood, while those inhabiting dry areas nest in the ground. Some ground-nesting species are also known to nest in crevices under rocks or within rock walls. Cleptoparasitic species appear to only attack ground or crevice nesters. Hylaeus species lack features required for digging or excavation; instead, it is likely that the holes they inhabit were initiated by other insects (such as Plagithmysus beetles or Ectemnius wasps).
In 2024 a new species, Hylaeus paumako, was discovered on the island Molokaʻi.
Hawaiian Hylaeus species include five known cleptoparasitic species. These are the only known cleptoparasitic colletids.
Australasia
New Zealand
8 species of Hylaeus are known in New Zealand. All of these species belong to the subgenus Prosopisteron. 6 of these species are endemic.
Endemic species of Hylaeus are divided into two groups based on a distinctive feature: the form of the apex of the 8th metasomal sternum of males. Hylaeus agilis and H. capitosus have a rounded apex, while H. kermadecensis, H. matamoko, H. murihiku and H. relegatus have a bifid (deeply notched) apex. Two species are adventive from Australia: Hylaeus asperithorax and H. perhumilis.
H. agilis has been recorded nesting in a wide variety of pre-made holes in stems and wood, for example in Muhlenbeckia australis and Ripogonum scandens, as well as introduced blackberry. Widespread throughout the three main islands, females are known to be aggressive pollen and/or nectar seekers, and have been observed on yellow mistletoe (Alepis flavida) and red mistletoe (Peraxilla tetrapetala).
H. asperithorax is found on the three main islands of New Zealand, as well as the Three Kings Islands and the Chicken Islands, Somes Island, and the Chatham Islands. Host plants are a mix of native plants (for example, Wahlenbergia pygmaea and Veronica speciosa) and introduced plants such as the common dandelion.
H. kermadecensis is restricted to the Kermadec Islands. H. kermadecensis has two known host plants: the native Scaevola gracilis and the introduced flossflower (Ageratum houstonianum). This species is also known to nest in previously excavated holes in wood and stems, and has been found using anobiid tunnels. It has been observing nesting in the trunk of Myrsine kermadecensis.
H. matamoko is a South Island species, found in mid- to southern montane areas. Host plants associated with these species include native Hebe spp., Epilobium spp. and Myosotis spp.
H. murihiku is also a South Island species, with specimens being collected from Fiordland. Little is currently known about biological behaviour and habits of the species.
H. perhumilis inhabits both the North and South Island. This species once again occupies pre-made holes to nest, and have been collected from both borer holes as well as those found in structures such as buildings and benches. Their host plants are known to be introduced Banksia spp and Eucalyptus regnans.
H. relegatus is widespread throughout the 3 main islands of New Zealand, and also the Chatham Islands and Three Kings Islands. They are known to utilise a wide range of both native and introduced plants across their range. They also utilise pre-excavated holes in wood and stems to nest, including those found in weatherboards and planking. Nests have been known to be parasitized by Gasteruption spp and Coelopencyrtus australis. Prepupae have also been recorded being attacked by Melittobia spp, and immature bees have been recorded as being killed by mould mites (Tyrophagus putrescentiae).
Australia There are 173 species of Hylaeus found in Australia. 14 out of 16 sugenera of Hylaeus found in Australia are endemic.
Phylogenetic data currently suggests that Hylaeus originates from Australia, arising around 30 million years ago. One dispersal event would have led to the species found in New Zealand, and another separate dispersal event leading to the worldwide distribution of species found outside Australasia, with both these events having occurred between 22 and 23 million years ago.
Subgenera found in Australia The Australian Faunal Directory lists 20 subgenera as being found in Australia:
Hylaeus (Analastoroides) Rayment, 1950: Hylaeus foveatus (Rayment, 1950) Hylaeus (Edriohylaeus) Michener, 1965: Hylaeus ofarrelli Michener, 1965 Hylaeus (Euprosopellus) Michener, 1965: Hylaeus certus (Cockerell, 1921); Hylaeus chrysaspis (Cockerell, 1910); Hylaeus dromedarius (Cockerell, 1910); Hylaeus pergibbosus Cockerell, 1926 Hylaeus (Euprosopis) Perkins, 1912: Hylaeus disjunctus (Cockerell, 1905); Hylaeus elegans (Smith, 1853); Hylaeus honestus (Smith, 1879); Hylaeus husela (Cockerell, 1910); Hylaeus violaceus (Smith, 1853) Hylaeus (Euprosopoides) Michener, 1965: Hylaeus amatus (Cockerell, 1909); Hylaeus cyanurus (W. Kirby, 1802); Hylaeus lubbocki (Cockerell, 1905); Hylaeus musgravei Cockerell, 1929; Hylaeus obtusatus (Smith, 1879); Hylaeus perplexus (Smith, 1854); Hylaeus rotundiceps (Smith, 1879); Hylaeus ruficeps (Smith, 1853) Hylaeus (Gephyrohylaeus) Michener, 1965: Hylaeus sculptus (Cockerell, 1911) Hylaeus (Gnathoprosopis) Perkins, 1912: Hylaeus albonitens (Cockerell, 1905); Hylaeus amiculiformis (Cockerell, 1909); Hylaeus amiculinus (Cockerell, 1922); Hylaeus amiculus (Smith, 1879); Hylaeus chromaticus (Cockerell, 1912); Hylaeus euxanthus (Cockerell, 1910); Hylaeus theodorei (Perkins, 1912) Hylaeus (Gnathoprosopoides) Michener, 1965: Hylaeus bituberculatus (Smith, 1879); Hylaeus philoleucus (Cockerell, 1910)