Mystrium

These ants are rarely encountered and for most species, poorly known. They are predacious, presumably of Chilopoda, but this has been confirmed in only a few species. Nests have been found under rocks or dry logs on the ground and in leaf litter. They lie motionless when disturbed. Their interesting reproductive modes, nesting behavior and colony dynamics have been examined in some species.

Identification
The mandibles are long and slender, with numerous (always more than 5) teeth which are similar in size and scattered along the inner margins, and with the tips rounded and with very short teeth. The frontal lobes extend only slightly forward of the antennal sockets and do not cover the clypeus when viewed from the front. The petiole has distinct front and upper faces but lacks a rear face, and its attachment to the gaster is broad and approximately the same height as the petiole so that the upper surfaces of petiole and gaster are separated by at most a shallow impression. The head and body have scattered hairs which are broad and rounded (spatulate).

The long, thin mandibles with rounded tips and the spatulate hairs on the head and body, as well as the shape of the head, are unique to these ants and will allow their ready identification.

Species Groups
Mystrium species groups

Biology
Species of the genus in Madagascar show two distinct reproductive strategies and associated colony structures (Molet et al. 2009). In Mystrium rogeri, each colony has a single dealate queen with a larger (flight) thorax than workers but mandibles are similar to those of the workers. In colonies of other species (e.g. Mystrium voeltzkowi, Molet et al. 2006), winged queens are lost and roughly half of the female adults belong to a caste of ergatoid queens which are smaller and allometrically distinct from workers. Only a few ergatoid queens are mated in each colony and they lay all the eggs, while virgin ergatoids behave as laborers inside the nest (e.g. brood care). Species lacking winged queens multiply by fission (Molet et al. 2009).

Bihn & Verhaagh (2007) - Besides their bizarre morphology, Mystrium ants have also evolved some novel biological traits. They have a unique defense mechanism in which they snap their mandibles to generate a powerful strike (Gronenberg et al. 1998; Moffett 1986). Molet et al. (2006) demonstrated that, in some species of Mystrium known from Madagascar, normal queens are replaced by wingless reproductives which are smaller than workers. Because Mystrium are rarely encountered, information on their general biology, ecology and behavior remains sparse.

Castes


Worker of M. camillae from the Northern Territory, Australia.

Nomenclature

 *  MYSTRIUM [Amblyoponinae]
 * Mystrium Roger, 1862a: 245. Type-species: Mystrium mysticum, by monotypy.

Yoshimura and Fisher (2014):

Diagnosis of female The characters uniquely observed in Mystrium within the subfamily Amblyoponinae are given in italics.

1. Compound eye present.

2. Posterior margin of head strongly expands posteriorly on each side.

3. Anterior margin of clypeus with specialized conical setae.

4. Spatulate setae present on clypeus mesal of mandible insertion (Fig. A).

5. Labrum lacking small dentiform setae arranged horizontally.

6. Palpal formula 4,3.

7. Distinct extension present on the distal edge of second labial palpomere (Fig. B).

8. Mandible linear without a distinct basal angle.

9. Masticatory margin of mandible with two rows of projections: true mandibular teeth on dorsal row and a series of basal denticles on the ventral row; basal ventral denticles larger than true mandibular teeth except for apical teeth.

10. At midlength of mandible, row of basal denticles arranged on ventral edge of man­dibular shaft, distant from mandibular teeth (Fig. C).

11. Mandible twisted inward so that apical tooth is located ventrally (Fig. D).

12. No basal large projection present on basal portion of mandibular inner margin.

13. Ridge present on apical portion of mandible, which is originally dividing ventral and inner surfaces of mandible, inserting dorsally to the apical tooth (Fig. A vs. B: Fulakora mystriops Brown, 1960, see comments).

14. Constriction between petiole and abdominal segment III present.

15. Cinctus 3, constriction between pre- and post-sclerites on abdominal segment IV, distinctly present.

16. One or two stout spines present on posterior portion of abdominal sternum VII (Fig. C).

17. Body surface with spatulate to squamose setae in some workers of all species.

Diagnosis of male The diagnostic characters uniquely observed in Mystrium within the subfamily Amblyoponinae are given in italics.

1. Frontal carinae present.

2. Anterior margin (=free margin) of clypeus with specialized conical setae.

3. Antenna consisting of 13 segments.

4. Mandible with single, blunt apical tooth.

5. Palpal formula 4,3.

6. Notaulus distinct or absent.

7. Mesepimeron often lacking distinct posterodorsal lobe (epimeral lobe).

8. Mesotibia with one or two spurs in most cases, rarely indistinct.

9. Metatibia with two spurs.

10. Distinct constriction present between petiole and abdominal segment III in dorsal view.

11. Abdominal segment IV with tergosternal fusion.

12. Pretergite of abdominal segment IV distinctly differentiated from posttergite, with the cinctus between them.

13. Pygostyles absent.

14. Distal margin of abdominal sternum IX convex.

15. Separation between basimere and telomere distinct.

16. Basal projection on cuspis well developed.

17. ''Basoventral portion of the aedeagus in lateral view extended basally, distal margin of extension rounded'' (Fig. D).

18. Serrate denticles present on basal portion of ventral margin of aedeagus in lateral view.

19. Pterostigma well developed on forewing.

20. Radial sector on forewing fully present.

21. Radial sector on forewing reaches costal margin.

22. 2r-rs on forewing connected with radial sector posterior to pterostigma.

23. 2rs-m present on forewing.

24. Position of cu-a on forewing variable, close to or far from junction between media and cubitus.

25. Radius present on hindwing.

26. 1rs-m present on hindwing.

27. Media on hindwing present apical to 1rs-m.