Amitermes

 Soldier and workers of Amitermes dentatus, from Termite Web.

Belongs within: Termitinae.
Contains: Drepanotermes.

Amitermes is a genus of termites whose soldiers possess long curved mandibles with one tooth present in each. Most species nest in small subterranean galleries, though some produce much larger nests. The magnetic termite Amitermes meridionalis of northern Australia builds narrow wedge-shaped mounds aligned in a north-south direction. Most species feed on dead wood but some may forage for dead leaves.

Species assigned to Amitermes are found throughout warmer regions of the world. Molecular phylogenetic analysis indicates that Amitermes is paraphyletic to the genus Drepanotermes (Inward et al. 2007) which was previously treated as a subgenus of Amitermes.

Ami-, Amitermes
Published 26 May 2016
Soldier of Amitermes, copyright Alexander Yelich.

I’ve referred before to my enthusiasm for termites, those wonderfully weird sociable scions of the cockroach clan. For today’s post, I’m looking at one of the larger and most widespread termite genera, Amitermes.

There are over 100 species of Amitermes found in tropical regions around the world, though they are most diverse in Africa and Australia. They are members of the so-called ‘higher termites’ of the Termitidae, those termites with a gut microbiota dominated by bacteria rather than protozoa. Soldiers of Amitermes have long sickle-shaped mandibles with a more-or-less well-developed tooth on each mandible; these mandibles are used to slash at perceived threats, the effect of this direct attack being presumably exacerbated by offensive chemicals that seep from the fontanelle, a pore on the front of the head capsule. Members of the genus are diverse in habits: some build sizable mounds above ground whereas others live in small colonies in underground tunnels. Some show a distinct preference for living in the nests of other termites, either moving into abandoned mounds after the original owners have perished or squatting in some overlooked corner of an active nest. Nests may be built directly around a food supply, or workers may go out to forage for food to bring home. In the latter case, the workers may construct a covered tunnel for themselves as they go; these trails may commonly be seen running along the ground in areas where such termites are abundant. Many Amitermes species feed on wood but they may also take other vegetable matter such as grass. A number of species feed on the dung of herbivorous mammals such as cattle or horses (Gay 1968), digesting parts of the consumed plant matter that the original feeder could not. One West African species, A. evuncifer, is a significant pest of crops, attacking root vegetables or the roots of young trees. Hill (1942) noted that mound-building Amitermes could present difficulties beyond just their feeding habits, explaining that “The frequent destruction of nest of [this genus] is perhaps the most important task of those employed in the maintenance of certain northern aircraft landing grounds, for the removal of the original nest almost invariably is followed the erection of another of a size and consistency that contributed a potentially dangerous obstacle to landing or rising aircraft“.

Magnetic termite mounds, copyright David King.

Perhaps the most famous members of this genus are the ‘magnetic termites’ of northern Australia. These are three species that build mounds that, instead of being conical or globular like the mounds of other species, are long and narrow, almost blade-like. Even more strikingly, they are lined up almost exactly along a North-South axis, with at most a 10° deviation. Experimental alterations of such mounds indicate that the termites are indeed sensitive to the direction of magnetic fields though other factors such as local climatic conditions may also play a part. The shape of magnetic mounds is usually interpreted as an adaptation for temperature regulation: at the cooler ends of the day, the mound is receiving the full effects of the sun but during the hot midday only the thin upper edge is in the line of the light. However elegant an explanation this may seem, however, it overlooks the detail that a more standard globular mound is actually better for heat regulation overall. Round mounds have a much lower surface area-volume ratio and hence a lower rate of heat diffusion. Blade-shaped mounds may absorb heat quickly in the morning but they also lose heat quickly at night. An alternative explanation for the mounds’ shape may lie in where magnetic mounds are found. It is worth noting that only one of the Amitermes species concerned, A. meridionalis, is an obligate constructor of blade-shaped mounds; the other two species, A. laurensis and A. vitiosus, may build either conical or blade mounds depending on local conditions. Magnetic mounds are constructed on flat flood plains, so the termites living inside them build up stores of grass to provide food when flood-waters prevent them from foraging outside the nest. By allowing better air flow within the nest than a conical mound, the blade-shaped mounds allow food stores to remain edible for longer, reducing the risk of them expiring before flood-waters recede (Korb 2011). Temperature regulation is still the best explanation for the regular orientation, of course, but is probably not the primary cause for the mound form overall.

Drepanotermes rubriceps soldiers around a nest entrance, copyright Lochman Transparencies.

Phylogenetic analysis of the termites by Inward et al. (2007) indicated that the genus Amitermes as currently recognised is probably not monophyletic, being paraphyletic to at least the Australian genus Drepanotermes. Members of this latter genus are grass-feeders, particularly on the hard Triodia (spinifex) grasses that dominate large parts of arid Australia (and which few animals without the super-charged termite digestive system can eat). In my experience, Drepanotermes are one of the few termite genera that can be reasonably easily recognised from the workers alone, which are noticeably longer in the legs than other termites. I’ve often seen Drepanotermes workers out foraging at night; the entrance to the underground nest (a simple hole) can usually be found nearby. The soldiers do not usually emerge from the nest, but a group of them will sit in the entrance hole with their heads poking out to provide defence. When collecting specimens, I’ve found that the challenge is to move fast enough to grab a soldier before it zips back into the tunnel, escaping your grasp.

Systematics of Amitermes

Characters (from Hill 1942, as Hamitermes, excluding Drepanotermes): Winged adult: Small to moderately large, mostly of dark colour. Head circular to broadly oval, rather thick, shallowly arched. Eyes rather small, not very prominent. Ocelli small to moderately large. Fontanelle in centre of head, or a little to the rear, distinct, usually oval, often with anterior prolongation. Postclypeus lighter in colour than head capsule, about half as long as wide, more or less strongly inflated; posterior margin markedly convex and anterior margin straight. Mandibular condyle very small. Anteclypeus usually well developed. Labrum broader than long. Left mandible with distal point of molar part projecting well beyond masticating edge. Antennae of 14-18 segments (usually 15); third segment usually shortest of all. Pronotum longer than half its breadth, more or less straight in front, usually same colour as head. Meso- and metanotum usually broad behind and not very deeply incised. Stumps of forewings a little long than hind ones. Wing membrane densely covered with micrasters and with sparse hairs. Median vein close to cubitus. Fore tibiae with two or three, mid and hind tibiae with two apical spurs. Cerci short. Styli absent. Soldier: Head rectangular, broadly rounded or distinctly longer than wide, in each case narrowed anteriorly. Fontanelle usually present and towards the front; fontanelle glands usually very large. Postclypeus bilobed and shortest in the middle. Labrum rounded or conical at apex. Mandibles usually narrow, sabre-shaped, with large basal part; outer edge usually bent convexly into an arch; inner edge usually with a well developed tooth, which may be directed forwards, inwards or backwards, or with only a suggestion of a tooth (indicated by slight expansion and/or thickening of edge). Antennae of 13-15 segments, usually 15. Pronotum narrower than head, saddle-shaped. Tibial spurs as in winged adult. Cerci short. Styli rudimentary or absent. Worker: Head broadly oval, sometimes richly pigmented. Postclypeus usually about half as long as broad. Left mandible as in winged adult. Antennae of 13-19 segments.

<==Amitermes Silvestri 1901 [=Hamitermes Silvestri 1903; incl. Monodontermes Silvestri 1909]H42
|--A. beaumontiIVE07
`--+--A. dentatusIVE07
|--A. evunciferIVE07
`--+--DrepanotermesIVE07
`--+--A. heterognathus Silvestri 1909IVE07, H42 [=Hamitermes (Monodontermes) heterognathusH42]
`--+--A. conformisIVE07
`--A. obeuntis Silvestri 1909IVE07, H42 [=Hamitermes obeuntisH42]

Amitermes incertae sedis:
A. abruptus Gay 1968J13
A. accinctus Gay 1968J13
A. amiferA50
‘Hamitermes’ capito Hill 1935H42
A. coachellaeN90
‘Hamitermes’ colonus Hill 1942H42
A. darwini Hill 1922J13 [=Hamitermes darwiniH42; incl. H. willingsi Hill 1935H42]
‘Hamitermes’ dentosus Hill 1935H42
A. emersoniN90
‘Hamitermes’ eucalypti Hill 1922H42
‘Hamitermes’ exilis Hill 1935H42
‘Hamitermes’ germanus (Hill 1915) [=Termes germana; incl. H. kimberleyensis Mjöberg 1920]H42
A. hartmeyeri (Silvestri 1909)J13 [=Monodontermes hartmeyeriH42, Hamitermes hartmeyeriH42]
‘Hamitermes’ herbertensis Mjöberg 1920H42
A. innoxius Gay 1968J13
A. inops Gay 1968J13
‘Hamitermes’ latidens Mjöberg 1920H42
‘Hamitermes’ lativentris Mjöberg 1920H42
A. laurensis Mjöberg 1920WG91, H42 (see below for synonymy)
A. longignathusSVT04
A. lonnbergianusH79
A. meridionalis (Froggatt 1898)WG91, H42 (see below for synonymy)
A. messinaeH79
A. minimusN90
‘Hamitermes’ modicus Hill 1942H42
A. neogermanus Hill 1922WG91, H42 [=Hamitermes neogermanusH42; incl. H. perplexus var. victoriensis Hill 1922H42]
‘Hamitermes’ obtusidens Mjöberg 1920H42
A. pallidiceps Gay 1969 [=A. pallidus Gay 1968 non Light 1932]G69
A. pandus Gay 1968J13
A. parvulusN90
‘Hamitermes’ parvus Hill 1922H42
A. pavidus Hill 1942J13 [=Hamitermes pavidusH42]
A. perarmatus (Silvestri 1909)J13 (see below for synonymy)
‘Hamitermes’ perelegans Hill 1935H42
‘Hamitermes’ ravus Hill 1942H42
‘Hamitermes’ scopulus Mjöberg 1920H42
A. silvestrianusN90
A. snyderiN90
A. subtilis Gay 1968J13
A. unidentatusS57
A. vicinusMC13
A. vitiosus Hill 1935WG91, H42 [=Hamitermes vitiosusH42]
‘Hamitermes’ westraliensis Hill 1928H42
A. wheeleriN90
A. xylophagus Hill 1935WG91, H42 [=Hamitermes xylophagusH42]

Amitermes laurensis Mjöberg 1920WG91, H42 [=Hamitermes laurensisH42; incl. H. perplexus Hill 1922 (preoc.)H42, H. wilsoni Hill 1922H42]

Amitermes meridionalis (Froggatt 1898)WG91, H42 [=Termes meridionalisH42, Hamitermes meridionalisH42, T. (Eutermes) meridionalisH42]

Amitermes perarmatus (Silvestri 1909)J13 [=Monodontermes perarmatusH42, Hamitermes perarmatusH42, H. perornatus (l. c.)H42]

*Type species of generic name indicated

References

[A50] Ahmad, M. 1950. The phylogeny of termite genera based on imago-worker mandibles. Bulletin of the American Museum of Natural History 95 (2): 37–86.

Gay, F. J. 1968. A contribution to the systematics of the genus Amitermes (Isoptera: Termitidae) in Australia. Australian Journal of Zoology 16: 405–457.

[G69] Gay, F. J. 1969. Amitermes pallidiceps, a new name for A. pallidus Gay (Isoptera: Termitidae). Journal of the Australian Entomological Society 8: 112.

[H42] Hill, G. F. 1942. Termites (Isoptera) from the Australian Region (including Australia, New Guinea and islands south of the Equator between 140°E. longitude and 170°W. longitude). Commonwealth of Australia Council for Scientific and Industrial Research: Melbourne.

[H79] Howse, P. E. 1979. The uniqueness of insect societies: aspects of defense and integration. In: Larwood, G., & B. R. Rosen (eds) Biology and Systematics of Colonial Organisms pp. 345–374. Academic Press: London.

[IVE07] Inward, D. J. G., A. P. Vogler & P. Eggleton. 2007. A comprehensive phylogenetic analysis of termites (Isoptera) illuminates key aspects of their evolutionary biology. Molecular Phylogenetics and Evolution 44: 953–967.

[J13] Jones, D. T. 2013. The termites of Barrow Island, Western Australia. Records of the Western Australian Museum Supplement 83: 241–244.

Korb, J. 2011. Termite mound architecture, from function to construction. In: Bignell, D. E., et al. (eds) Biology of Termites: A Modern Synthesis pp. 349–373. Springer.

[MC13] Majer, J. D., S. K. Callan, K. Edwards, N. R. Gunawardene & C. K. Taylor. 2013. Baseline survey of the terrestrial invertebrate fauna of Barrow Island. Records of the Western Australian Museum Supplement 83: 13–112.

[N90] Nutting, W. L. 1990. Insecta: Isoptera. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 997–1032. John Wiley & Sones: New York.

[S57] Seevers, C. H. 1957. A monograph on the termitophilous Staphylinidae (Coleoptera). Fieldiana Zoology 40: 1–334.

[SVT04] Sornnuwat, Y., C. Vongkaluang & Y. Takematsu. 2004. A systematic key to termites of Thailand. Kasetsart Journal of Natural Science 38 (3): 349–368.

[WG91] Watson, J. A. L., & F. J. Gay. 1991. Isoptera (termites). In: CSIRO. The Insects of Australia: A textbook for students and research workers vol. 1 pp. 330–347. Melbourne University Press: Carlton (Victoria).

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