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Termite magnetism. (journal extracts).

ONE of the natural wonders of the Northern Territory is the mound of the magnetic or compass termite (Amitermes meridionalis).

The mounds of these grass-feeding termites are built on seasonally flooded plains, resemble massed mud tombstones and stand 1.5-2 metres tall. Remarkably, all are oriented in a north-south direction. Studies indicate that one of the benefits of this alignment is a stable temperature for the termites, but how does a colony of small blind termites manage to orientate the mound during construction? What cues does it use?

An obvious cue is the Earth's magnetic field, in particular the magnetic declination, or the direction of the horizontal component of the magnetic field. Many animal species, including insects and migrating birds, rely on cues from the geomagnetic field as it provides reliable and constant directional information. In some bacteria, magnetic forces acting on tiny grains of magnetite (magnetised iron oxide) within the bacterium can literally orient the whole organism, much like a compass needle!

Dr Peter Jacklyn of the Northern Territory University, and Dr Ursula Munro of the University of Technology, Sydney, have investigated magnetic mound building cues in Amitermes. As part of his PhD, Jacklyn decided to observe magnetic cues during mound repair, so he cut the top 10-15 cm off eight mounds at each of four sites near Darwin and manipulated the magnetic field experienced by the termites by burying powerful bar magnets in the mound, below the cut surface.

Five months later he took photographs of cross-sections through the repaired mound to analyse the orientation of internal mud cells. The cell orientations within untreated mounds tend to reflect the orientation of the mound itself, and the scientists reckoned that the mechanisms used to align the internal cells are likely to be used to help orient the whole mound. They looked at the relationship between the direction of the imposed magnetic fields and the orientation of the many individual 'repair' cells.

At first glance, there was no evidence of magnetic cues influencing termite mound construction, but the story for the internal architecture of the mounds is less clear cut. Cell orientations were definitely altered by the artificial magnetic fields, but not in a straightforward manner.

Shifting the declination by 45[degrees] to the east or west shifted the pattern of orientation of internal mound cells, but not exactly corresponding to the 45[degrees] shift in the magnetic cues. Jacklyn and Munro say the most likely explanation for this is that the blind termite workers are responding to a combination of magnetic cues and the orientation of the uncut mound.

Jacklyn PM and Munro U (2002) Evidence for the use of magnetic cues in mound construction by the termite Amitermes meridionalis (Isoptera: Termitinae). Australian Journal of Zoology, 50:357-368.
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Author:Davidson, Steve
Geographic Code:8AUST
Date:Apr 1, 2003
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