INTRODUCTION / SUBFAMILY / GENUS

The ant subfamily Formicinae is a large and successful group, comprising about 3030 described species, distributed globally across a wide range of terrestrial environments

The new phylogeny of the Formicinae reveals six strongly supported, species-rich clades, and five other species-poor, long-branched lineages whose positions in the tree are less certain.

The five taxonomically isolated lineages correspond to the genera Gesomyrmex, Gigantiops, Myrmoteras, Oecophylla, and Santschiella.

In the last article we explored one of these isolated lineages, The Amber Javelin Ants - Gesomyrmex, which you can read about here.

But this time we will talk about Myrmoteras!

Species of the genus Myrmoteras are among the most bizarre ant forms and unique among Formicinae by having mandibles that form into a specialized trap-jaw mechanism that can open more than 280 degrees. – a character that, however, has convergently evolved in other subfamilies (Odontomachus and Anochetus in Ponerinae; Dacetini in Myrmicinae). The small Myrmoteras ants with cryptic living habits in leaf litter make them difficult to collect.

The genus Myrmoteras was established by Forel in 1893 from a series of workers taken in the Thaungyin Valley, Burmah. This ant, to which he gave the name binghami (genus genotype), was for a number of years the only known representative of the genus.

The genus Myrmoteras, which comprises circa 41 species, is endemic to the Asian tropics.

This ant genus shows one of the most peculiar morphologies among Asian tropical ants, however, biological information is very limited.

Moffett categorized several different species in two morphologically distinct subgenera:

1 - Myrmoteras Forel, 1893 and

2 - Myagroteras Moffett, 1985

The differences between them will be clarified later in the Morphology Chapter.

COMMON NAME

Myrmoteras is a combination of two Greek words - myrmex which means ant and teras, which means marvel, wonder or monster.

Among the Discord Asia channel community we enjoy the monster definition more.

As such, I think a good common name for this genus would be The Monstrous Ants, but please let me know if you have other suggestions based on the other meanings.

As a side note: I am also heavily interested in roaches nowadays and one interesting aspect of roach keeping is the apparent freedom of commonly naming species for the sake of the hobby. For example, roach genus would get a common name, and specific species inside those genus would get the same name plus another adjective or noun that best suits them specifically. So for example, in the case of Myrmoteras binghamii (the species I am currently keeping), since binghamii is referencing Charles Thomas Bingham who was an Irish military officer and entomologist, the common name for this species would be Bingham’s Monstrous Ant, cool wouldn’t you think?

DISTRIBUTION

The genus is strictly confined to the old world tropics.

China, India, Sri Lanka, Borneo, Indonesia, Malaysia, Myanmar, Thailand, Vietnam and the Philippines.

To date the recorded northern limit of the range of myrmoteras is just north of Latitude 14 degrees.

CASTES

This genus presents three castes:

1 - Queen caste

2 - Worker caste

3 - Male caste

Queen-worker dimorphism in body size is exceedingly small and the worker caste is considered monomorphic. Even for the first workers, which are not considered being nanitic (head width 1.16 mm), although slightly smaller than the workers in the largest field-collected colony (head width 1.19 + SD 0.03 mm) for some reasons we will see later.

DIVISION OF LABOR

The average colony size for the genus is considered very small, with less than 20 workers per colony. To present knowledge, the colony size of this genus is among the smallest so far known for ants.

Small colony size is a common phenomenon in Myrmoteras. In the subfamily Formicinae, colony size is generally large with more than 100 workers. Comparable species to Myrmoteras in terms of colony size are found in the subfamily Ponerinae which can also have small colonies with an average of 10 workers.

On such small colonies, it's normal to observe one mated queen alongside other virgin dealate queens and some workers.

The behavioral specialization of queens seems weak. Virgin dealate queens in Myrmoteras will forage in a similar way as workers as well as both alate and dealate virgin queens will exhibit brood care

A reduction in morphological specialization, especially of the thorax structure, may make such worker-like behavior possible for queens.

MORPHOLOGY

As said before there are two Myrmoteras subgenera recognized and there are a couple of morphology differences but we will just present one of them.

In the subgenus Myrmoteras a pair of long trigger hairs extends from the labrum; in the new subgenus Myagroteras the trigger hairs are absent.

Inverted colors and painted over the trigger hair for easier visualization

There is a correlation between the length of the trigger hairs and the length of the mandibles, this ensures that the external object which springs the trap will be within the grasp of the closing mandibles and should be impaled on the apical prongs.

Trap-jaw ants are characterized by high-speed mandibles used for prey capture and defense. Power-amplified mandibles have independently evolved at least four times among ants, with each lineage using different structures as a latch, spring and trigger, but Myagroteras do not possess the hair trigger mechanism.

Myrmoteras binghamii worker with extended mandibles

The behavior of Myagroteras species has not been studied. However, it seems reasonable to assume that the presence or absence of trigger hairs must bear directly on differences in foraging behavior between the two groups, and therefore probably is a reﬂection of significant ecological differences, and thus provide a reason for the big eyes in Myrmoteras, implying that they may use their eyes for detection, localization, and even for release of the strike.

Actually, Myrmoteras workers may also likely use visual cues to detect, localize and catch prey, but their visual abilities have not been studied in detail.

Besides belonging to the Trap Jaw Ants group, Myrmoteras also belong to the macrophthalmic group, or large-eyed, tropical ants, namely, ant genus like the Formicinae Gigantiops, Opisthopsis, Oecophylla, Gesomyrmex, Dimorphomyrmex, and Santschiella, the Myrmeciinae Myrmecia and Ponerinea Harpegnathos, and I may add also the whole subfamily Pseudomyrmecinae.

LIFE CYCLE

There are only a few references about their life cycle, which are observations from keeping Myrmoteras colonies under laboratory conditions, since I haven’t had enough time to witness their life cycle and brood development. Nevertheless, I will leave you the results of the laboratory observations for your reference.

All colonies were kept at 25°C and a 12 h:12 h light:dark cycle.

Colonies were kept in artificial nests measuring 9.5 x 6.2 x 2.8 cm which contained a small box (3.6 x 3.6 x 1.4 cm) as a nest chamber. The floor of both the chamber and foraging arena was made by plaster of Paris in order to keep the humidity sufficiently high.

My Myrmoteras binghamii colony during their re-housing

Springtails, small termite nymphs, small nymphs of the myrmecophilous cricket Myrmecophilus formosanus, and small nymphs of Gryllus bimaculatus were given as prey.

Ants were given water and sugar ad libitum and fed three times a week.

“The first worker emerged 11 months after we collected the founding queen. The queen frequently foraged, and hunted for prey before the emergence of workers. During this solitary period, she produced brood, although a few cocoons disappeared. We do not know whether the long duration for the production of the first worker is the normal condition or an artifact due to the laboratory condition. Three months after the emergence of the first worker, the colony grew up to 5 workers, at that stage also the first alate queen was produced.”

From my own experiences I can report the following:

I received a colony with 2 Queens and 20 workers on the 13th December 2021 without any brood.

One and half months later, they had already laid eggs, and those eggs hatched into small larvae.

Now precisely three months after receiving the colony, the larvae are growing very well, and probably ready to pupate, which would match the same development periods reported on the laboratory observations of 3 months for complete brood cycle. In my case, we would need to account for probably 2 weeks for egg laying period and lower developmental rate, as we just went through a short winter period, hence my colony haven;t fully developed pupae yet.

My Myrmoteras binghamii colony and their larvae and micro larvae

REPRODUCTIVE STRATEGY

Among the subfamily Formicinae, the majority of independent founding species show claustral colony foundation. Known exceptions so far are a few species of Polyrhachis, and Cataglyphis nigra.

Claustral colony foundation usually goes along with the production of nanitic workers, however, such small workers do not seem efficient for a predatory lifestyle on live arthropods. Actually, claustral colony foundation is rarely found in ponerine ants in which the majority of species are predators, whereas it is often found in formicoid ants where omnivorous ants are common.

The overall biological information provided clearly indicates that the genus Myrmoteras is one of the most peculiar ants among the subfamily Formicinae. Small colony size, predatory lifestyle, and less specialization of queens seem to be an ancestral condition.

Myrmoteras ants are predators on small arthropods, therefore non-claustral colony foundation may be mandatory for the production of functional workers that must be sufficiently large for predation.

Myrmoteras shows non-claustral colony foundation. The thorax structure of queens without reduction of the pronotum is in agreement with their non-claustral colony foundation, indicating worker-like neck muscles, hence queens are able to hunt during independent foundation (non-claustral ICF), as also referenced above from the laboratory observations.

NEST AND COLONY COMPOSITION

In the wild , Myrmoteras can be found among the leaf litter fauna in moist tropical forest, from lowland up to montane forests. Most Myrmoteras specimens have been collected from leaf litter samples from beneath rotting logs as well as under stones.

It turns out that this type of ants which are rarely found have a high correlation to both soil temperature and air temperature. This means that the higher the soil temperature and air temperature, the less probable it is to be able to find this ant genus, as they would occur on shaded forests.

Here are two descriptions of collections of a wild colonies of Myrmoteras:

1 - “The colony was collected at an elevation of about 900 meters in relatively open, secondary forest which extended in a narrow band between the cultivated valley and a wide expanse of primary forest farther in. I discovered the ants by recognizing one individual just as it disappeared beneath a dead leaf in the litter. Overturning the leaf I found a group of about twelve Myrmoteras workers with brood. Apparently the ants had been tightly clustered where two leaves lay in contact. The leaves were slightly moist and were loose within the litter. A cluster of six ants (including one dealate queen) was then located on the exposed surface of a leaf fragment which had most likely fallen to the side when I lifted the first leaf. The ants appeared undisturbed by the exposed situation, but, once disturbed directly with a forceps, the they proved excellent sprinters. During the next four hours the leaf litter was carefully searched out to about four meters in every direction. Four individuals were collected during the first half hour, all within a meter of the original colony location. One of these workers carried a microlarvae. Altogether 22 workers were collected, as well as 1 queen, 7 pupae, and a number of larvae and eggs. This was apparently the entire colony.”

Myrmoteras binghamii Worker and Queen side view

2 - “The colony was found at an elevation of about 100 meters in disturbed primary forest. A worker was located in leaf litter. She was capable of startling bursts of speed, rushing to the underside of a leaf every time I moved my hand to within 20 cm. After capturing a springtail, the ant walked 30 cm from her original location to the nest. The nest was in a narrow, centimeter-deep crevice in the soil beneath the litter with a wide (1.0 X 0.3 cm) entrance. It contained a dealate queen, two alate gynes, workers, and brood. Altogether eight workers were collected, including two foragers taken during an hour of observations of the nest entrance. The surrounding ground was searched thoroughly for additional ants, but none were found within a five meter radius of the nest. My assumption is that this was the complete colony.”

My Myrmoteras binghamii colony with egg clutch and micro larvae

The colony composition and behavioral characteristics of the trap-jaw ants Myrmoteras were also studied in laboratory conditions.

The following colony characteristics were observed:

1 - Colony size was remarkably small, less than 10 workers on average with one mated dealate queen.

2 - Alate sexuals were produced in colonies with less than 10 workers.

3 - Body size difference between queens and workers was not conspicuous: head width of queens was just 1.1 times bigger than that of workers.

4 - Worker body size in small colonies was not significantly different from that in large colonies.

5 - Virgin queens showed worker-like behavior.

6 - Finally, a solitary queen of Myrmoteras that was kept in the laboratory showed non-claustral colony foundation. After producing five workers, an alate queen emerged.

The brood tends to be scattered or laid side by side, except for small clumps of eggs and microlarvae.

NEST DEFENSE

Myrmoteras have two main defensive mechanisms. Their mandibles and, since they belong to the Formicinae, formic acid.

The defensive response of the workers is elicited by virtually any small invertebrate approaching the nest site (slow-moving isopods were usually ignored). Although many of the intruders, such as tiny beetles and cockroach nymphs, were most likely innocuous, others, such as ants of a variety of species, represented likely threats.

My Myrmoteras binghamii workers in defensive mandible position

Most often the intruder was hard-bodied, in which case the ant’s mandibles usually ricocheted off the cuticular surface. However, if the mandibles penetrated the integument, the intruder could be captured and eaten.

The Myrmoteras can swing its gaster under its body, for spraying its adversary with defensive secretions. Workers can also grip a leg of an adversary and spray them. This represents a typical formicine response to enemy attack.

FORAGING AND FEEDING

The workers are observed in primary and second growth tropical evergreen forest, and can normally be found foraging during daylight hours on the ground and over low herbaceous vegetation.

Myrmoteras are specialized predators on small arthropods like collembolans, but as detailed before they can also prey on other soft bodied invertebrates such as small termites and termite nymphs, small nymphs of crickets and even smaller isopods.

My Myrmoteras binghamii colony hunting springtails

While foraging, workers will keep their mandibles fully opened. Once they encountered prey animals, they slowly approached them. When they can be sufficiently close to have the prey within reach of the tips of the trigger hairs, they will strike their prey by very quickly snapping the elongate mandibles.

Closing the mandibles is normally powerful enough to kill the soft body arthropods they hunt for.

Other trap jaw and snap jaw ants employ spring-loaded ‘snapping jaws’ to amplify the force of their mandibles and allow them to numb their prey.

Myrmoteras on the other hand, impale the prey. Springtails have very fast escape responses, so it is likely that the trap-jaw mechanism in Myrmoteras evolved to facilitate the capture of these arthropods,

Prey are typically held far out in the mandibles, gripped in the most distal mandibular teeth, the same teeth that penetrated the prey during the strike.

Myrmoteras binghamii worker masticating a springtail

The feeding process begins with the mastication of the prey. She opens her mandibles until they disengage from the corpse, then closes them again, applying enough pressure for the most distal teeth to sink deep into the prey. This laborious ‘chewing ’ behavior is often repeated several times. Finally the ant moves forward until her mouthparts contact the fluids oozing from the new punctures. The worker drinks for several seconds to a minute, and then backs up and repeats the chewing process.

After the foragers had fed on the prey they retrieved, they passed the masticated prey on to the larvae, fellow workers or both virgin and reproductive queens. When prey size was large, a few ants cooperatively masticated it.

Inside the nest chamber, trophallaxis among female individuals was often observed. Mated queens frequently received trophallaxis from workers.

Myrmoteras binghamii worker grooming itself

During throphallaxis, a recently fed worker is frequently approached by another ant and is solicited for regurgitation. The positions adopted by the ants during trophallaxis varied greatly. Both ants could hold their mandibles in any position. However, most often the donor’s mandibles were closed, which forced the other individual to crouch down and twist its head and trunk to the side to reach up at the mouthparts of the donor. In other cases both workers leaned to the sides, with their heads tilted as much as 90° so that their mouthparts could make contact.

EXTRA BEHAVIORAL NOTES

“In both Acanthomyrmex notabilis and A. ferox, workers frequently held immatures passively in their mandibles for long periods, even during intervals of colony quiescence. Similar behavior has been observed for workers of the trap-jawed formicine ant Myrmoteras toro (Moffett, in press). The brood holding behavior in both cases seems to represent a means of ensuring that workers can rapidly disperse with brood whenever the colony is disturbed. This is a particularly useful strategy for ants nesting in exposed sites where disturbances are common. As in the A.ferox colony described here, the Myrmoteras colony, which consisted of 22 workers and one queen, had been nesting between leaves lying loose within leaf litter on the forest floor. Another common trait of Acanthomyrmex, Myrmoteras toro, and many other ants with small colonies (including colonies of many ants at an early stage of growth after the first brood has been raised by the queen,E.O. Wilson: pers. comm.)”

CONCLUSION

Hope you have enjoyed reading this article about the “The Monstrous Ants”

Myrmoteras, also known as The Monstrous Ants

Thank you for your time once again, maybe I should do a video about them as well. What do you think?

I am in absolute awe with this small species of ants. They are so fascinating and interesting. Such a multitude of behaviors and characteristics. It was absolutely wonderful to do this research and study more about them.

Cheers!

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