Are termitaria of Nasutitermes triodiae the largest faecal structures on Earth?
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Are the 6 m-high termitaria (https://www.collinsdictionary.com/dictionary/english/termitarium) of the spinifex termite (Nasutitermes triodiae, https://en.wikipedia.org/wiki/Nasutitermes_triodiae and https://bie.ala.org.au/species/urn:lsid:biodiversity.org.au:afd.taxon:08d68974-09a8-4965-b274-ec4182f8dd0e), the largest mainly faecal structures on the planet?
It is reasonable to assume that faeces, unlike biomineralized structures such as coral reefs, cannot accumulate in natural conditions because they tend to decompose.
If this were true, the only large accumulations of faeces to be found on Earth would be those occurring in large caves, inhabited by colonies of bats. Here, faeces are preserved because of cold, dry conditions, and the limited rate of decomposition of chitin.
It is well-known that termites use faeces to build their shelters in the form of 'carton'.
Therefore, most naturalists might assume that the largest termitaria of carton are made by arboreal termites, and weigh no more than 50 kilograms. These are situated in trees, and belong to Nasutitermes spp., such as Nasutitermes corniger (https://www.inaturalist.org/taxa/122701-Nasutitermes-corniger) of central and South America
However, I invite readers to consider the following.
(Please bear in mind that the enormous structures built by Macrotermes (https://www.istockphoto.com/photo/termite-mound-in-african-wildlife-reserve-gm1154943913-314240815 and https://www.inaturalist.org/observations?place_id=any&taxon_id=346639&view=species) and Syntermes (https://www.science.org/content/article/these-termite-mounds-are-so-big-you-can-see-them-space) are mounds, not termitaria.)
The largest termitaria on Earth occur in tropical Australia. They reach about 7 metres high (Hill 1942, https://catalogue.nla.gov.au/Record/1021273), with a mass of possibly 5 tonnes.
This is 100-fold heavier than the largest carton termitaria belonging to the same genus (Isoptera: Termitidae: Nasutitermitinae: Nasutitermes).
The photo below appears in a commercial website with no data, but it looks like being a record in height: http://www.termite.com.au/images/termitemound.jpg. I do not know how tall the person is, for scale. However, assuming that he/she is of average height, I calculate that this termitarium is at least 6.2 m high.
Assuming that a Land Rover weighs 2 tonnes, and would weigh double that amount if filled with earth, I estimate the mass of the termitarium shown in the following to be at perhaps 7 tonnes: http://2.bp.blogspot.com/_JwTvDWpU4xI/S8t5VQ0PtAI/AAAAAAAABP0/CcZbeLj1m0I/s1600/termitemound01.jpg.
Further illustrations:
https://sightseeingtoursaustralia.com.au/attractions/cathedral-termite-mounds/
https://www.agefotostock.com/age/en/details-photo/spinifex-or-cathedral-termites-nasutitermes-triodiae-mounds-dominating-the-landscape-in-the-open-forested-lowlands-such-complex-structures-provide-flood-free/UIG-961-09-law01745
scroll in https://oddculture.com/biggest-animal-made-structures-in-the-world/
https://www.inaturalist.org/observations/109033193
https://www.inaturalist.org/observations/98704154
https://www.inaturalist.org/observations/98312272
https://www.inaturalist.org/observations/93447816
https://www.researchgate.net/figure/The-giant-mounds-of-the-Cathedral-termite-Nasutitermes-triodiae-are-a-spectacular_fig2_283572562
https://www.experiencethewild.com.au/?p=Wildlife-Database-Info&ID=4
https://www.alamy.com/stock-photo-giant-termite-mound-in-recently-burnt-dry-season-savannah-woodland-27833024.html?imageid=7625DC81-C9BC-4E16-89CF-F9AA4FE0DAC9&p=11297&pn=1&searchId=8c85598d8d9d2d3eb471dc12f26be93e&searchtype=0
https://www.alamy.com/stock-photo-our-car-beside-giant-termite-mound-beside-kakadu-highway-north-from-16239244.html?imageid=F92277B1-3F2B-4E61-81F6-D3342BE40B0B&p=31451&pn=1&searchId=8c85598d8d9d2d3eb471dc12f26be93e&searchtype=0
What has been overlooked is the possibility that these termitaria, which are built mainly of clay by the spinifex termite (https://www.inaturalist.org/taxa/154588-Nasutitermes-triodiae), consist mainly of material that has been ingested and then defaecated.
The diet of this species consists mainly of dead leaves of the ligneous, pyrophilic grass Triodia (https://images.auscape.com.au/photographer-galleries/reg-morrison/savannah-spinifex-termite-mounds-triodia-sp-21190705.html and https://www.inaturalist.org/observations?place_id=any&taxon_id=132351&view=species).
In the past, it has been assumed that the clay used by the spinifex termite is carried in the jaws of the worker caste, as occurs in most other termites. However, there are four reasons to suspect that most of this clay is passed as mineral faeces.
Firstly, the spinifex termite is the only member of its genus to build clay termitaria. This species remains similar in body form to the arboreal species that build with carton, or in some cases build no visible termitaria.
Since all other members of this genus rely on ligneous faeces for construction, and none transports ligneous materials by mouth, it would be consistent with this pattern if the spinifex termite were to retain this method of transporting its building materials. This would mean a shift from purely organic matter to mainly mineral matter (clay, mainly kaolinitic, https://en.wikipedia.org/wiki/Kaolinite).
Secondly, the spinifex termite has a slow pace of life, based on an extremely nutrient-poor diet. This limits the speed of construction and repair. However, this need not be prohibitive, because the termitaria of this species last centuries, rather than decades.
Thirdly, no member of this subfamily (i.e. Nasutitermitinae) of termites is known to tunnel deep into the earth. This means that the limits on gut capacity could theoretically be compensated by the frequency possible where each collecting foray is short.
Fourthly, the spinifex termite has an incentive to practise geophagy (i.e. supplementation of trace elements and other mineral nutrients by means of eating earth in addition to its main food of organic matter, https://en.wikipedia.org/wiki/Geophagia). This is because its food plants are extremely nutrient-poor. Furthermore, it is likely to have particular demands for catalysts (e.g. cobalt, https://en.wikipedia.org/wiki/Cobalt_in_biology) on account of the symbiotic nitrogen-fixation (https://en.wikipedia.org/wiki/Nitrogen_fixation) performed by bacteria in the gut of termite workers.
It is conceivable that workers of the spinifex termite divide their time, spending periods eating, and then switching to construction. If so, they would avoid the need to mix organic matter and clay in their guts.
According to this rationale, workers of the spinifex termite could achieve two ends by swallowing clay-rich earth on a routine basis, and defaecating it for the construction/repair of the termitarium. These two ends are
- the transport of the building-material, and
- the geophagic supplementation of their nutritional requirements, by absorption of certain nutrients from the clay.
Comments
I have the following two references to the maximum heights of the termitaria of N. triodiae.
Andersen and Jacklyn (1993), in ‘Termites of the Top End’, state ‘They are amongst the largest mounds built by termites anywhere in the world, sometimes exceeding 6 m in height.’
Calaby and Gay (1959), in ‘The Australian fauna and its relationships’, state, on page 220: ‘It builds huge mounds which may be columnar structures over 20 ft high. Nests of this magnitude are unique in the genus Nasutitermes.'
Also see http://www.termite.com.au/images/termitemound.jpg.
I have before me the book ‘Termites: a study in social behaviour’ by P E Howse.
On pp. 86-87, Howse states of of Nasutitermes triodiae that “the so-called fluted or columnar nests ... can occasionally attain the staggering height nearly 7 1/2 m.” He implies that the source of this information is: Hill G F 1942 Termites (Isoptera) of the Australian region. Melbourne (https://catalogue.nla.gov.au/Record/1021273).
He goes on to write:
“According to Hill...there is no well-defined nursery, but the queen and brood are found at about ground level in the nest. The food consists of grass, which is cut in large quantities in the dry season and stored in peripheral chambers in the bulges or flutes.”
Please also note that Hill (1942) seems to be a suitable reference for the fact that the whole structure built by N. triodiae is above ground.
The following confirms the occurrence of Nasutitermes triodiae in New Guinea: https://www.publish.csiro.au/IS/IT9960507.
https://www.researchgate.net/publication/232679439_Synonymy_of_two_arboreal_termites_Isoptera_Termitidae_Nasutitermitinae_Nasutitermes_corniger_from_the_neotropics_and_N_polygynus_from_New_Guinea
https://www.cabdirect.org/cabdirect/abstract/20013153692
https://www.researchgate.net/publication/313915699_Parallel_evolution_of_mound-building_and_grass-feeding_in_Australian_nasute_termites
Nasutitermes triodiae a complete disappointment in terms of ability to support termite-eaters:
Something easily overlooked about the enormous structures built by Nasutitermes triodiae in northern Australia is that this is the ultimate example of ‘false promise’, in terms of the ability of this termite to support termite-eating animals.
Here we have the largest termitaria on Earth. And the close relatives of N. triodiae, both within the same genus (please see paper below, showing that tamanduas specialise on congeners in South America) and within the same subfamily (e.g. Trinervitermes, which sustains the largest specialised termite-eater on Earth, viz the aardwolf), certainly are productive enough to support termite-eaters. But there seems to be hardly anything going on in terms of animals eating N. triodiae, which is ultimately a reflection of the poor soils of the habitat of N. triodiae (as indicated by Triodia itself) and the fact that it eats mainly a sclerophyllous, pyrophilic grass rejected by mammalian grazers with the exception of one or two slow-growing marsupials such as the Macropus robustus group.
In short, not only does N. triodiae build the largest of all termitaria on Earth, but these structures symbolise the greatest possible disappointment in terms of actual productivity. Not only does its habitat lack any counterparts for edentate anteaters, or aardvarks, or aardwolf, but even the two myrmecophagous vertebrates which do occur in Australia are either scarce and not particularly interested in N. triodiae (echidna) or completely absent from this part of Australia (numbat).
The tall termitaria of N. triodiae are monuments to ecological sterility, as it were.
http://www.jstor.org/discover/10.2307/2387872?uid=2&uid=4&sid=21104472192231
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