A rare beetle's first flight
What luck!
We happened to be prowling the forest this week, cameras at the ready, when I spotted this beautiful beetle. Its behaviour suggests it was just emerging from its larval home inside a rotting log. A newly-minted adult beetle, shiny and perfect. For half an hour we watched on as it became increasingly mobile and alert … and then took flight.
Now, such a sight would be pleasing at any time … but this is a special beetle. Not only is it a species we’ve never seen before, but it seems that sightings are exceedingly rare anywhere!
I believe it is Chlorobapta bestii (Scarabaeidae: Cetoniinae) – and if so, there is currently just a single photographic record of this flower chafer on the Atlas of Living Australia (ALA). Our photos will appear there very soon, via iNaturalist, and we’ll be keen to hear what the beetle gurus out there think.
Did I get the ID right? Is this sighting as special as it seems?
The species was discovered way back …
The original species description of Chlorobapta bestii was published 180 years ago, based on a female beetle collected from Norfolk Island and added to an Englishman’s private beetle collection. The entomologist and illustrator John Obadiah Westwood is the author - hence the beautiful line drawing that accompanied the species description.
This very beetle – now 180 years old –is probably one of the five million insect specimens, including thousands of holotypes, currently housed in the Oxford University Museum of Natural History. She’s a rather long way from home.
The original image of Chlorobapta bestii. At the time (1842) Westwood gave the name as Schizorhina bestii. The species was later moved to the genus Chlorobapta.
Extract from Plate 28, page 102 (ref. 1)
As wonderful as the line drawing is, a bit more information is needed. Westwood’s description provides details of colour and the features he believed distinguished it from other species. But first I need Paul’s help to decipher the Latin!
extract from Westwood, 1842 (ref. 1), page 103
translation (by Paul Whitington) of Westwood’s Latin description of Chlorobapta bestii … perhaps an imperfect interpretation, but good enough for our purposes, for now
So our beetle seems a good match. The black areas are slightly more extensive on ours. For example, the yellow of the lateral margin of the pronotum does not completely enclose the black ‘spot’, and the clypeus has 2 rather than 3 tiny yellowish spots. However, Moeseneder et. al (2019, ref 2) point out that melanic forms are common among Australian species in the tribe to which Chlorobapta belongs … so I think our beetle simply has more black than the one examined by Westwood.
Another possible candidate species is Chlorobapta frontalis, but I believe I can safely exclude it.
C. frontalis is a more commonly sighted species and there are numerous published images. Those images show obviously different markings to our beetle – most notably the shape of the green stripes on the elytra. But to cross-check, I found an early published description – it too highlights the “oblique green bands”.
extract from W. Macleay, 1862 (p. 15, ref 3)
Note that his Schizorhina viridisignata was later synonymised with Chlorobapta frontalis
Based on the historical museum records on ALA, the distribution of Chlorobapta bestii extends from northern NSW to Melbourne. And east to Norfolk Island. So we sit well within the species’ known range.
… but it is now seldom seen.
There is currently just one record of Chlorobapta bestii on iNaturalist … a dead beetle found in January 2019 near Nowra, NSW (link). In contrast, there is a similar sized and equally distinctive cousin to C. bestii, the ‘Fiddler Beetle’ Eupoecila australasiae … of which there are currently 466 sightings on iNaturalist! Proof that naturalists keenly photograph beetles like this – when they see them.
Even ALA has just 24 records for Chlorobapta bestii (cf 834 for Eupoecila australasiae !), and most of these were collected many decades ago.
A beetle’s life
So what can we surmise about the beetle we photographed this week?
This is based on a bit of guesswork and extrapolation from what is known of its relatives. I can find no information specific to Chloroblapta bestii and even knowledge of the genus is scant (ref. 2).
It has spent many, many months feeding on decaying wood inside a dead tree. Perhaps as much as 3 years!
There is every reason to believe it had only just emerged. The behaviour matched that of a brand new adult. Slow moving at first, with no bodily damage or signs of wear, gradually becoming more mobile and responsive. And then taking flight, up into the forest canopy.
So the stump where we found it was almost certainly its larval home.
The stump is actually a round cut from a Eucalyptus tree that fell (on our water tank!) immediately after the January 2020 fire. The tree was alive but well-rotted through the centre.
So there’s a good chance that this beetle was a young grub at the time of the fire, safely buried deep inside a standing tree. And it was lucky to escape the chainsaw when we cut up the fallen wood and carted the rounds aside to use as track markers!
The rotting wood upon which the beetle appeared. The tree fell in the immediate aftermath of the January 2020 fire, and was clearly well-rotten at that stage. Its decomposition continues now, even as the rounds cut from it serve as trail markers in the forest just 50m from where it once grew.
It will now seek a mate and will probably not live a lot longer. Unlike most other flower chafers (Scarabaeidae: Cetoniinae), Chlorobapta adults are not typically found feeding on flowers. But if this one does seek a nectar or pollen meal, it has timed its emergence just right. The surrounding Angophora trees are heavy with blossom.
Male or female? At this stage I’m not sure – perhaps a beetle expert will be able to tell me. But I’m leaning toward it being a female. Beetles in this genus show little difference between the sexes, but males may have enlarged antennal clubs, modified legs and perhaps concave abdomens (ref. 2). The antennae on our beetle appear much as in Westwood’s diagram, it is quite large (28-30mm in length), and round-bodied.
Finally, here are a few more photos. Perhaps a particular angle, on a particular body part, will prove useful in confirming the species identity or sex.
We chose not to collect it, even though at the time we guessed it might prove scientifically valuable. Instead we decided to simply watch on, take a bunch of photos, and let it fly free.
We are very glad we did. It was a rather special moment to see it slowly spiralling skyward.
Update (pm, 19/1/22)
We’ve just heard from entomologists Paul Hutchinson and Chris Moeseneder, via iNaturalist … and it’s confirmed!
It is indeed Chlorobapta bestii.
It is a special and rare sighting.
Our photos and observations do make a useful contribution to the ongoing taxonomic study of this group.
And it is a male.
Thanks Paul, thanks Chris!
Now our quest is to find some Chlorobapta bestii grubs to see exactly where and how they live. And ideally to collect a specimen or two for DNA analysis. Perhaps we’ll get lucky – again.
Click here to see the sighting on iNaturalist.
References
Westwood, J.O. 1842. Descriptions of some new species of Cetoniidae, from Australia, Asia and the Asiatic Islands. Arcana Entomologica: or Illustrations of New, Rare, and Interesting Insects. 1: 102-104. Available from Biodiversity Heritage Library (link)
Moeseneder, C.H., Weir. T.A., Lemann, C. & Hutchinson, P.M. 2019. Scarabaeidae: Cetoniinae Leach, 1815, in Australian Beetles Volume 2, Ch. 34. Ślipiński, A. & Lawrence, J.F. (eds). CSIRO Publishing, Clayton South, Vic.
MacLeay, W. 1862. Description of twenty new species of Australian Coleoptera, belonging to the families Cicindelidae and Cetoniidae. Transactions of the Entomological Society of New South Wales, v1, 9-21. Available from Biodiversity Heritage Library (link)