Quietly riding off into the sunset

By Athayde Tonhasca

In 2019, four American and Australian enthusiasts set off to Indonesia on a bold mission: to find the Wallace’s giant bee, Megachile pluto. This bee was first described in 1858 by naturalist, explorer and co-author of the theory of evolution Alfred Russel Wallace (1823-1913). After its official discovery, the Wallace’s giant bee – aka the giant mason bee – disappeared from the records and was thought to be extinct until it was rediscovered in 1981. The bee vanished again for the next 37 years, until the 2019 search expedition: the team found and filmed the Wallace’s giant bee. 

A female Wallace’s giant bee and a worker honey bee © Abalg, Wikipedia Creative Commons

Denizens of tropical jungles are expected to be elusive and mysterious, but the Wallace’s giant bee lives up to its name: it is the largest bee on Earth. If a bee of this size can go unnoticed and believed to be extinct for most of its recorded history, it’s not surprising that less spectacular species can go unrecorded for a long time. The bee Pharohylaeus lactiferus, sighted this year in Australia, was previously seen in 1923; the bone skipper fly (Thyreophora cynophila) was first described in 1794, remained undetected until 1850, then disappeared again until its rediscovery in Spain in 2009. There are many other examples of what is known as ‘Lazarus fauna’: species believed to be gone, only to ‘come back from the dead’ when rediscovered.

Extinct… Not. The bee P. lactiferus (© Natural History Museum, Wikipedia Creative Commons) and the fly T. cynophila (© Carles-Tolrá et al. 2011, Boletín de la Sociedad Entomológica Aragonesa 48: 217‒220)

Small size and secretive lives are only partially responsible for the patchy or absent recording of insect species: rarity is a huge factor. 

Rarity is one of the quirks of life on Earth; for almost every ecological community (a group of species living in the same location), most species are represented by few individuals, and most individuals belong to a few common species. Reams of paper and gallons of ink have been spent trying to explain why it is so, with no consensus so far. Whatever the explanation, there are many rare species and only a few common species.

Relative species abundance of beetles sampled from the river Thames © Aedrake09, Wikipedia Creative Commons

Rarity is a big headache for conservationists because for most species it is difficult to say with confidence they are declining or no longer present (i.e., extinct): some of them may just have been overlooked because of low numbers or obscure existences. The International Union for Conservation of Nature (IUCN) considers a species extinct when ‘there is no reasonable doubt that the last individual member has died’. This is a sensible approach, but ‘no reasonable doubt’ is a tall order for insects. So it is not surprising that the IUCN has registered fewer than 50 extinct insect species worldwide, and that the list of 23 American species declared extinct last month by the Fish and Wildlife Service does not include any insects: conservationists just don’t have enough data.

The Wallace’s giant bee may be a naturally rare species, but much of its habitat has been wiped out and replaced by crop fields and palm oil plantations. So it may very well become extinct. But if it does, it will take us many years to know. 

These uncertainties are vexing and underplay the trouble faced by insects. The only way to deal with the problem is by keeping a finger on the pulse of populations to notice signs of decline, and this is done by meticulous, long-term monitoring. Thanks to the work of enthusiastic and determined volunteers, we know that in Britain at least thirty species of larger moths have become 40% less abundant in the last 10 years, on average the distribution of 112 species of solitary bees have contracted between 1980 and 2013, and over 40% of dragonfly species have increased since 1970. As incomplete and tentative as these figures are, they reflect Britain’s long tradition of biological recording. We have only a nebulous idea of what’s happening in most of the world. 

Serendipitous rediscoveries of species thought to be extinct are heart-warming, but they are far and between. Considering the relentless shrinkage of natural habitats across the globe, species vanishings are more likely to be permanent. By monitoring, we can raise the alarm and trigger action. If we don’t monitor, inconspicuous species, the very fabric of biodiversity, may slip quietly into oblivion. 

The Franklin’s bumblebee (Bombus franklini), last seen in the western United States in 2006: perhaps gone forever © Project Noah