‘A very ordinary’ bee: The enigmatic Leioproctus philonesus

About 600 kilometres across the Pacific Ocean from the coast of New South Wales, on subtropical Lord Howe Island, lives a fairly plain little bee species called Leioproctus philonesus. These bees are about 10 mm long, and like most other Leioproctus species they are black and hairy. This species was first described in 1929 by Theodore Cockerell, one of the most prolific taxonomists in history, from a single specimen collected on the island in January 1922. Cockerell thought this bee’s appearance so plain that he referred to it as ‘a very ordinary species’. One feature does make L. philonesus stand out from some of its relatives though; the beautiful bright orange scopae on the hind legs of the females. Scopae are densely hairy parts of female bees’ bodies that they pack with pollen at flowers so that it can be carried back to the nest and fed to their offspring.

A Leioproctus philonesus female specimen, showing the brilliant dense orange scopa on her hind leg (Photo by Laurence Packer©)

Since Cockerell’s original description, only one other L. philonesus specimen has been collected on the Island. It was another female, and she was found in 1980. Male specimens remain elusive and unknown. Apart from the female’s physical appearance, little else is known about L. philonesus. Presumably they are solitary bees and nest in tunnels in the ground like other closely related species do, but this has not been observed. Despite there being over 170 different Leioproctus species across Australia, L. philonesus is the only one found on Lord Howe Island. Known from nowhere else in world, L. philonesus has persisted on Lord Howe Island for who knows how long, quietly doing its thing, hidden away from the inquisitive eyes of bee researchers.

That is until the spring of 2010, when, on the Atherton Tableland of far north Queensland, a few L. philonesus individuals were found foraging on flowers of the north Queensland endemic rainforest tree Sarcopteryx reticulata. This was unexpected, to say the least. The Atherton Tableland is over 2000 km from Lord Howe Island. These bees were found during part of a PhD project looking at the effects of habitat fragmentation on native bee communities, and specimens were sent to the Australian Museum for specialist taxonomist identification. The confirmed presence of L. philonesus both on Lord Howe Island and on the Atherton Tableland, but without a single record anywhere else, provides a very interesting biogeographical mystery.

Mountainous forests on Lord Howe Island, left (photo by Steve Smith©), and the Atherton Tableland rainforest from which the north Queensland Leioproctus philonesus specimens were found, right (photo by Tobias Smith©)

The north Queensland specimens include both females and males, so one small but fairly important part of the story is now solved. Cockerell would probably have thought the males even more ordinary than the females: They’re black and hairy, but as male bees don’t collect pollen or care for young, they lack the attractive orange scopae on their hind legs.

With L. philonesus now known from north Queensland as well as Lord Howe Island, there are yet more unknowns about this species than there were before. Foremost among them: why do we find these bees where we do today? Are the two known populations isolated relicts of a once much more widespread distribution, or has one of these two populations established from a lucky dispersal event from the other? How long have they been apart? These will be hard questions to answer, but using fresh specimens and modern genetic tools, answers are within reach.

But is it still possible to collect fresh specimens from Lord Howe Island? The species has not been recorded there since 1980. It is possible that it has become extinct. Probably more likely, though, is that it has not been recorded since then, simply because no one has looked for it. Could there also be further populations of this species in remote areas of the Australian mainland where bee researchers have not looked? So many interesting unknowns.

The 'ordinary' but enigmatic Leioproctus philonesus is just one of countless mysteries to be found in the world of Australian bee taxonomy. Let’s hope we can get to the bottom of some of these sometime soon.

© Tobias Smith 2020