Pale brown Myrmecia sp. 1 (Myrmecia cf. pilosula)

An interesting phenomena of jack jumper populations are the occasional sightings of paler, brown workers among normally coloured nests. Studies on the mainland have demonstrated that abnormal colouring in jack jumpers are caused by a gregarine protozoan parasite (Crosland 1988). Critical infection occurs at the larval stage where a gregarine spore (oocyst) will be ingested. Infestation of the parasite prior to the pupal stage interferes with cuticle darkening and hardening during pupal development. Thus infected young workers eclose variously paler and softer than their normally coloured ‘healthier’ sisters,  with strength of effect directly related to the level of infection. The affected workers retain these characters for the remainder of their life. Brown jack jumpers tend to have reduced lifespans and thus will usually only be found late summer to winter, correlating with the seasonal emergence of young workers.

Demonstration of gregarine infestation in a Tasmanian jack jumper (Myrmecia pilosula)

A brown jack jumper worker (Fig. 3) found foraging in the company of a normally coloured nest-mate (a western race Myrmecia pilosula) was collected from a nest in Buckland in mid April (2017). The ant was placed in a freezer for 24 hours, then removed and allowed to thaw. The gaster was dissected between the first and second gastral segments, and carefully removed to reveal the crop and stomach (Fig. 1).

The digestive tract revealed a large number of gametocysts (white spheres), which is typical of invertebrates with gregarine infestation. Even with just a macro lens these structures are quite evident (Fig. 1). Under a dissecting microscope the individual spores (oocysts) formed within the gametocysts are readily seen (Fig. 2). At a higher magnification than shown in figure 2 numerous free oocysts, which are characterictically lemon-shaped, were also observed in the gaster haemolymph.

The bulk of the Myrmecia observed below appear to be Myrmecia pilosula. Since gregarines are species specific parasites, it may be the case that it is a single gregarine species infecting these jack jumpers. Another <href=”https://tasmanianinsectfieldguide.com/pale-brown-myrmecia-sp-2″>Myrmecia species (Myrmecia cf. fulvipes) with apparent gregarine infection has also been observed.

It has been our observation that foraging brown jack jumpers tend to be less aggressive, and thus far more tolerant of harassing photographers than is typically seen in normally coloured jack jumpers.

          

M. pilosula (western race)
Early April 2015
Buckland

   

Myrmecia cf. pilosula
Late June 2017
Knocklofty Reserve, Hobart

 

Early July 2021
Knocklofty Reserve, Hobart/nipaluna
 

Myrmecia cf. pilosula
Late June 2015
Mt Nelson
This brown jack jumper is the darkest included here, showing how variable the ‘browning’ can be.

 

References

Crosland, M. W. J. 1988. Effect of a gregarine parasite on the color of Myrmecia pilosula (Hymenoptera: Formicidae). Annals of the Entomological Society of America 81: 481-484.

Omoto, C. K., and D. C. Cartwright. 2003. Investigating the diversity of parasitic protozoa using gregarine parasites of invertebrates. Pages 77-85, in Tested studies for laboratory teaching, Volume 24 (M. A. O’Donnell, Editor). Proceedings of the 24th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 334 pages.