Dissecting Cane Toads for Kimberley Toad Busters
During WW-II I was very lucky to have been sent by plane to live with my Australian grandmother in Melbourne to escape the threat of a possible Japanese invasion while my father remained behind in China. When, in 1947, my father took me to Holland, his homeland, I was sad to leave Australia. Since then I always longed to go back to the country where I had spent such happy times as a kid. It wasn’t until 1988, the year of the Bicentennial, that I eventually made my way back for a short stay to visit friends and relatives. In 1999 I made a second trip back, this time touring the coast of Queensland and stopping in Cairns.
From 2000 till 2011 my wife and I lived most of the year in the Provence region in southern France. The climate and vegetation were very attractive for insects so I was able to further develop my interest in beetles. Besides collecting a wide range of beetles, I collaborated with a Dutch and a French author on an award-winning book on Leaf beetles of France and recently co-authored a book on Jewel beetles of the Vaucluse department.
Soon after its publication I read that the cane toads had passed into Western Australia. Since I had learned about their destructive invasion while I was in Cairns, I had followed their devastating progress and impact on Australian wildlife with horror. When I read about the Kimberley Toad Busters’ programme and their need for volunteers I quickly contacted them. Possibly this could be an opportunity to help the conservation of the unique Australian fauna even if it was only in a very small way. I considered myself very lucky to be accepted.
Aim of the project
After being accepted as a volunteer with Kimberley Toad Busters for a period in June/July of 2014 it was decided my main activity would be to provide some insight as to the impact the cane toads were having on the local invertebrate populations, but limited to the distribution of insects and other food specimens found in the stomachs of collected cane toads. My research would be incorporated in the Marella Gorge Cane Toad project based at Nicholson Station.
To be able to do so I would dissect a certain amount of cane toads. Jordy Groffen, a young Dutch scientist, being responsible for the project, decided that identification of the insects found in the stomachs would only be necessary down to Order level, in this case distinguishing between Coleoptera and Hymenoptera.
In this paper we mainly use the popular name of ‘Cane Toad’, scientifically this toad is/was generally known as Bufo marinus, but recently scientists have discovered it should be called Rhinella marina.
Methods and means
Collecting and euthanizing cane toads
The cane toads designated for dissection would be mainly captured in the water bodies of the Marella Gorge. As the cane toads are diurnal collecting was done just after dusk, the toads were put in large plastic bags awaiting transport to Nicholson Station.
The prevailing order of capture and euthanizing of the cane toads was: collecting in the evening and keeping the toads in a plastic bag until the next morning when euthanizing took place. The result of keeping the toads alive during the night and part of the morning was that digestion could continue. This in turn made it harder to unravel the contents of the stomachs, so in order to improve this process it was decided to euthanize the toads with Dettol as soon as possible after returning to the Station and subsequently conserving the toads in deepfreeze containers until they could be dissected.
Although the centre of interest was to find out how much and what the cane toads had devoured and were devouring since their arrival in the Marella Gorge area it was decided to wait with toad busting until the last planned survey had taken place by July 16. But as it became evident that the toads were not present in the same numbers as expected, it was decided to start collecting them earlier in order to have enough subject matter.
Preservation of beetles
As my main interest would be focused on identifying beetles as well as possible, it would be necessary to preserve those beetles for later identification as it would not be possible for me to identify these Australian beetles at first glance. Preservation could either be done in a suitable chemical fluid or by mounting on cardboard. A suitable chemical for preserving insects so that they can be subsequently prepared for mounting is Ethanol; as only Methanol was available and insects preserved in this liquid are no longer suitable for preparation for mounting (legs and antennae remain stiff and thus cannot be manipulated) it was decided to discontinue the use of Methanol and preserve captured and euthanized cane toads in deepfreeze containers until preparation and mounting could take place.
Dissecting cane toads
Dissection of the cane toads from Marella Gorge started on 3 July 2014.
In the following weeks 644 objects were dislodged from the stomachs of 41 cane toads. Of these objects 25 turned out to be pebbles or small stones and 7 of the cane toads had empty stomachs. So eventually 34 stomachs were researched and 619 insects, spiders, etc. were detected using a stereo microscope to distinguish among the mush. That amounts to an average of 18 per stomach, to a maximum of 113 in one stomach. (For an example of the contents of 1 stomach: see photo 2.)
Results of the dissections
A breakdown of the main categories encountered shows 484 Ants (78%), 99 Beetles (16%) and 36 Miscellaneous items (6%) totalling 619 objects. (For a detailed breakdown of the stomach contents encountered: see fig. 1.)
Ants were divided into 5 categories, encountered in the following numbers: 248 red, 168 black, 23 big red, 10 big black and 35 bull ants, totalling 484 ants or 78% of the specimens researched.
Beetles accounted for 16% of the objects dissected. The distribution of families seems to show a rather unbalanced picture: more than half of the 99 specimens accounted not being further identified to family-level. This unbalanced distribution is explained in the fact that cane toads prefer smaller insects including beetles that are mainly found in the small to very small category i.e. 3-4 mm and less. Taking into account the wide variety of beetle species and even beetle families it becomes clear that in the partly digested contents of a cane toad’s stomach it is very difficult to further identify these small insects in more detail.
Cane toads show a preference for dark-coloured prey and are attracted by elongate forms and by movement. The beetles identified by family fit these characteristics: Ground beetles (Carabidae), Darkling beetles (Tenebrionidae), Checkered beetles (Cleridae), Leaf beetles (Chrysomelidae), Click beetles (Elateridae) and Scarab beetles (Scarabaeidae). Of these the Darkling beetles deserve special mention as it can be assumed that they share the same habitat where cane toads converge as the dry season progresses. In one case 24 of the same species were extracted from one cane toad stomach (see photo 3). Photos 4 and 5 show identifiable beetles that were dislodged from the dissected cane toads.
In the Miscellaneous group that accounted for 36 items or 6% of the objects excluding stones, the following items were encountered: caterpillars, centipedes, cockroaches, grasshoppers, moths, shield bugs, spiders, wasps and woodlice. Furthermore 25 very small rocks and stones were encountered, possibly ‘consumed’ as a response to the movement of the stone rolling down the slope of the embankment.
Before starting on my ‘lab’ work I was taken on a tour of the Marella Gorge research area to get acquainted with the methods of fencing off the area, setting traps to catch small local fauna and inspecting the surroundings looking for other small local fauna.
It is evident that the Dry season is not favourable for collecting large numbers of insects. Many that are overwintering do so in larval stage or even still as eggs, others that overwinter as adults do so in the ground or under the thick bark of trees that offer shade. During the Wet season there is a strong influx of the number of insects both in numbers per species as in the variety of species.
What are the main conclusions to be arrived at as a result of this research that was carried out during the Dry season in an area designated by a team of Kimberley Toad Busters as Marella Gorge and complemented by irregular captures of cane toads at Nicholson Station Homestead?
From such a limited research it would be foolish to try and reach important conclusions. This research should be merely regarded as a start-up, possibly as an example for further research.
As there are no similar researches to be found concerning this area bordering on the Kimberley, (although we have heard that similar research has taken place) nor comparisons in this area comparing Wet and Dry seasons firm conclusions are very hard to reach. But the results presented here are in compliance with general conclusions published concerning extensive research in other parts of northern Australia.
It was believed that cane toads would congregate towards water bodies as the dry season progresses as the cane toads need regular intake of moisture to avoid desiccation. It could thus be expected that cane toads would encounter and consume insects and other small fauna that consider those surroundings as their permanent or temporary residence. Whether or not the encountered variety of beetles is a representative sample of the beetles in the Marella Gorge area can only be determined by further and more extensive research on the subject.
First of all I want to thank Lee Scott-Virtue (founder, president and spokesperson of Kimberley Toad Busters) for accepting me as a volunteer with the Kimberley Toad Busters and for the exceptional hospitality I enjoyed during my stay. Travelling over the Highway and the dirt roads from Kununurra and viewing the arid landscape as we neared Nicholson Station it was amazing to see what an oasis Nicholson Station turned out to be and how enjoyable it was to walk around the grounds enjoying the fabulous vegetation, the birds and the dogs.
Soon I discovered that the outstanding upkeep of the station was very much due to the work of Dean Goodgame seconded by Lee. The generating of all electricity needed to keep the whole of the station in working order: the lighting, pumps, telephone and internet, garden appliances, cooling and freezing systems. All that at over 300 kilometres from civilisation.
Then there is Jordy Groffen, the young Dutch scientist, responsible for the daily management of the Cane Toad Project concentrated at the Marella Gorge, who took me for a guided tour of the Gorge with his Irish assistants Tiarnan Browne and Niamh Nolan to show me where the main event was taking place out in the open whereas I was stuck in my indoor lab. That was very considerate of him; it helped me feel part of the team and proved what a beautiful part of Australia this mainly barren area with its hidden gorges really was. Jordy explained just what was expected of me, how to deal with the toads, how to dissect them properly and record what I had encountered.
Thanks to you all.