Myrmecia tarsata

Myrmecia tarsataClassification
Subfamily: Myrmeciinae
Family: Formicidae
Order: Hymenoptera
Common name: Giant Bull Ant

These are day active (in the summer atleast) large bull ants. I have only seen two nests of this species so far and both had a single nest entrance. This species is distinctly polymorphic, with atleast four different morphs quite apparent in the field. Unlike other large Bull ants (M. pyriformis, M. nigriceps), these ants are infact active during the day. They have a distinct iridescence on their cuticle and a purplish green lustre when seen under bright sunlight. The apical segments of the gaster are yellowish red in colour.

Identification key (from Australian Ants Online):

1. Mandibles each with 4 or more enlarged teeth apart from that at the apex.
2. Larger teeth on mandible, apart from the apical denticle, numbering 4 or 5; head as long as broad or almost so (Cl > 90); mandibles at most slightly longer than head (MI never > 120).
3. Dorsal edges of frontal carinae barely anteriorly divergent.
4. Pronotum dark chocolate brown to black.
5. Anterior face of petiolar node vertical; dorsal surface of gaster not pubescent; apical portion of gaster yellowish red.

The yellowish red coloured apical segments of the gaster of Myrmecia tarsata.

These are not ants of different colonies, but are of the same nest. The ant on the right held the other ant and dragged it out of the nest holding the other by its mandibles and released the strong hold after displacing the ants nearly 2-3 m away from the nest. The ant on the right then returned to the nest hurriedly, while the one who was dragged away spent a large amount of time searching and never returned to the nest. I initially thought the worker who was thrown out maybe an aged worker who was removed from the nest, but then the worker was really fast, and displayed no sluggish movements. Such a behaviour of throwing out workers occurs commonly in the Ponerine Diacamma and Harpegnathos and is perhaps explainable as in both these ants exists a morph called 'gamergates' who can take over the colony from an ageing queen. The ones who stealthily try laying eggs in the presence of a Queen are either subdued in this manner (or by nipping of node like thoracic appendages called 'gemmae' in case of Diacamma) or the queen simply eats up the eggs. This made me wonder whether such gamergates known to occur commonly in Ponerines, are known in this primitive ant subfamily at all. Well, I then found a recent article which basically showed that Myrmecia pyriformis, does infact have gamergates.

Here is the reference.
Dietemann V, Peeters C and Holldobler B. 2004. Gamergates in the Australian ant subfamily Myrmeciinae. Naturwissenschaften 91: 432-435.

This is now really exciting and throws open a possibility of gamergates occurring in this particular species too. More fun questions to address!

Collected:
Mt. Majura, Canberra, ACT, Australia (2007).
Naggi National park, NSW, Australia (January 2007).

External links:
Myrmecia tarsata

Myrmecia nigriceps

Myrmecia nigricepsClassification
Subfamily: Myrmeciinae
Family: Formicidae
Order: Hymenoptera
Common name: Giant Bull Ant

These are large Bullants, with the smallest morph measuring around 13 mm, i.e., larger than the Jackjumper M. pilosula. In the summer months, these ants begin foraging early in the evening. They feed on a variety of insects, spiders and also on the sap of gum trees. They are polymorphic, with atleast 4 distinct morphs. I witnessed a sort of a partial nuptial flight, wherein only winged males flew out of the nest, but unfortunately never got to see the alate female. Nests, as in several species of Myrmecia, are terrestrial and have multiple entrances.

Identification key (from Australian Ants Online):

1. Apical segment of gaster blackish; anterior face of petiolar node more or less inclined posteriorly.
2. Mandibular shaft narrow at the extreme base, broadened over the basal 1/4 to 1/5 of its length.
3. Clypeus yellowish, concolorous with mandibles.
4. Hairs on head and mesosoma thin and sparse, those on sides near posterior corners of head not extending beyond outer margins of eyes.
5. Scape with numerous erect or suberect hairs.
   

A forager of Myrmecia nigriceps begins to clean up the nest at the onset of foraging in early evening.

This is the male of Myrmecia nigriceps: notice the reduced scape, raised pronotum, massive eyes and ocelli.

More pictures of Males of this species are here

Collected:
ANU campus, Canberra, ACT, Australia (2006, 2007).
Mt Majura, Canberra ACT, Australia (2007).

External Links:
Myrmecia nigriceps