The Giant Forest Ant, Jewel of Southeast Asia

The ENSING Blog features posts by our members about their research, observations and interests. This post was written by Mark Wong, who studies ants. Header image of a D. gigas alate courtesy of Eunice Soh. 

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Giant forest ants, Dinomyrmex gigas, are a familiar and unforgettable sight in Singapore’s nature reserves. These spectacularly robust ants can be found marching along and across forest trails, as if oblivious to our presence. Formerly Camponotus gigas, these ants were recently given a nice little genus of their own, Dinomyrmex. Belonging to the ant subfamily Formicinae, giant forest ants do not possess stings; for defense, they bite and use hairs on the ends of their abdomens to ‘paint’ formic acid onto their enemies. The impressive majors (i.e., the largest, big-headed workers) can deliver quite a painful bite – so it’s probably not a good idea to pick them up. That being said, these ants are generally shy and unaggressive, and as far as giant ants go, they are certainly the gentlest (see below).

In this post I’ve consolidated some basic information on the fascinating ecology and biology of giant forest ants – it’s for anyone who’s revelled at these magnificent creatures up close and would like to know more. Some of this information is also available on a detailed wikispaces entry which fellow ENSING ant researcher Gordon Yong previously made for his undergraduate work. Relevant scientific publications on giant forest ants are also listed at the end of this post.

I’ve always been pleased knowing that a small country like Singapore plays home to one of the biggest ants in the world. However, as there have only been a few proper studies on giant forest ants (and none in Singapore), there is still a lot that we don’t know about these rubies of our forests.

Just how giant?

Giant forest ants (D. gigas) can reach and exceed 3 centimetres, making them the largest ants in Asia, and certainly among the top contenders for the largest ants in the world. Here’s a summary that’s modified after Archibald et al. (2011), with images of the species further below. (Note that they aren’t ranked in any particular order)

1. Giant forest ant, Dinomyrmex gigas, from Southeast Asia. The queens average slightly over 31 mm in length, and major workers approximately 28 mm, but can reach 30 mm. These ants don’t sting, and are the gentlest of the lot.
2. Giant Amazon ants, Dinoponera spp., from tropical Brazil, Bolivia and Peru. Several species of this genus reach and may exceed 30 mm in length. They lack morphologically distinct worker and queen castes. These ants sting too.
3. Bull ant, Myrmecia brevinoda, from Eastern Australia. The major workers reach 36 mm and queens 31 mm in length. These ants have (really) painful stings.
4. Driver ant, Dorylus wilverthi, from equatorial Africa. The massive dichthadiiform queens of this army ant species reach a whopping 52 mm long! However, their workers, which sting and bite, are much smaller.

The world’s giantest giant ants. 1 – Dinomyrmex gigas, 2 – Dinoponera australis, 3 – Myrmecina brevinoda, 4 – Dorylus wilverthi. (Sources: 1 – Steve Shattuck, 2- Alex Wild, 3- Bill & Mark Bell, 4 – Will Ericson, AntWeb. All images public domain)

Where are they found?

Giant forest ants inhabit rainforests throughout Southeast Asia. They have been recorded in Thailand, Malaysia, Singapore, Sumatra and Borneo; their occurrence in the Philippines is uncertain. Interestingly, a subspecies with striking yellow legs, Dinomyrmex gigas boreensis, is found in southern Borneo.

Left: Global distribution of giant forest ants (Dinomyrmex gigas), from antmaps.org, an interactive platform providing distribution maps for thousands of the world’s ants. Right: The yellow-legged subspecies Dinomyrmex gigas boreensis at Kubah National Park, Sarawak (Source: Eunice Soh)

In Singapore, populations of giant forest ants appear to be restricted to primary and old secondary forests of the Central Catchment Nature Reserve and Bukit Timah Nature Reserve. In these areas, the gentle giants may often be seen foraging along trails, even occasionally straying to open patches of grass (see video below). However, as no studies have ever been conducted on the distribution and status of these ants in Singapore, it is unknown where their true ranges are, or whether there is even sufficient habitat to support local populations in the long term.

How do they live?

Big area, many nests. Colonies of giant forest ants can number 7000 individuals, and are polydomous – that is, they occupy several (probably 8 to 14) nests that are distributed throughout their habitat. This strategy, together with their large body size, enables them to cover vast foraging areas compared to other ants. A single colony in Sabah had a foraging range of 0.8 hectares – almost the size of a soccer field! The nests of these ants are usually constructed in soil between the buttress roots of emergent trees, and within the hollows of fallen or decaying trunks. One of these nests harbours the only egg-laying individual in the entire colony – the queen (giant forest ant colonies are monogynous, meaning they only have one queen; some other ant species have multiple queens in a colony, and are thus polygynous). Aside from the queen, the rest of the colony typically comprises workers – sterile female ants that do all the work. There are major workers (large, big-headed) which are mainly involved in defense, and minor workers (smaller, small-headed) which are involved in everything else – tasks such as foraging, maintaining nests, and tending to the queen and brood. (In the grassy video above, the first ant that appears is a major, followed by a minor. The video of the nest below also shows minors.) During the breeding season, the colony also produces alates  – winged reproductive males and females, which will eventually fly off to mate. After mating, female alates drop their wings and become queens of new colonies. (The header image of this blogpost shows a female alate. There are also nice images of the different castes at this blog post.)

The nightly sugar rush. Giant forest ants are predominantly nocturnal. At dusk, they can be seen congregating at the entrance of their nests, before suddenly leaving in large numbers within a short span of 50 minutes. This exodus of foragers then heads up into the canopy through a complex highway network running along branches, fallen trees, bamboo stands and hanging vines. The ants locate and scurry up their favourite trees in search of a particular group of insects. You see, like many other ants, giant forest ants obtain much of their carbohydrates in the form of ‘honeydew’ – a sugary cocktail excreted by sap-sucking insects. In Sabah, the ants were observed collecting honeydew from wax cicadas (Bythopsyrna circulata) – large insects with round wings and a white-black swirly pattern, sort of like a lollipop. The collection of honeydew from the cicadas is non-invasive, but a little tricky; the ants have to position themselves close to the cicadas, and capture honeydew droplets as they are continuously flicked out by the insects.

Giant forest ants collecting honeydew from wax cicadas. (Source: Martin Pfeiffer)

In addition to carbohydrate-rich honeydew, giant forest ants supplement their diets with nitrogen. They obtain this from capturing prey insects such as winged termites, and also feeding off bird droppings. In the video below you can see several of the ants with swollen gasters (abdomens) containing honeydew, as well as others carrying termites between their jaws. (The troublesome finger in the video was meant to provide a sense of scale).

Ritualistic showdowns. Interestingly, giant forest ants do not like other giant forest ants. Each colony is highly territorial, and will defend its nesting and foraging areas from other colonies of giant forest ants. As a consequence, the large home ranges of separate giant forest ant colonies do not overlap with one another – this suggests that their populations might be limited by access to nesting and foraging sites in smaller and fragmented forests, such as those in Singapore. Perhaps the most exciting aspect of their territoriality; majors of neighbouring colonies engage in ritualistic one-to-one tournaments. Two majors representing the two neighbouring colonies will meet at a fixed location, and do battle through a series of kung-fu-like actions: drumming the ground with their legs and gasters, exchanging boxes and leg-sweeps with their antennae and front legs, and occasionally escalating into an all-out mandible-grabbing tug-of-war. A single win however does not stop the confrontation, with the majors taking a break by retreating to their territories and grooming their antennae and legs; before returning to the tournament site to fight again. These intense battles can last for as long as 30 days(!), however they rarely result in the death of either gladiator. (Unfortunately I don’t have a video of this amazing behaviour, but if any of our readers do we’d be very happy to feature them).

Ritualistic fighting between majors of D. gigas. (Source: Martin Pfeiffer)

Why should we care?

The giant forest ant is an iconic and irreplaceable element of Southeast Asian biodiversity, and there are many reasons why we should take a timely interest in these animals. Here are just some off the top of my head:

Wider ecological communities are likely to depend on them. They have associations with canopy insects, and, being large-sized, abundant invertebrates, are perhaps also an important food source for a variety of mammals, birds, reptiles and amphibians.

Their large and abundant nests may contribute to significant amounts of soil aeration, nutrient-cycling and decomposition – crucial processes that maintain the overall health of forest ecosystems.

Their territoriality, large home ranges and apparent dependence on undisturbed, mature forests suggests that there might be few available habitats for this species as deforestation and forest fragmentation continues.

Finally, only through understanding and conservation will future generations have the same opportunities to marvel at these remarkable creatures. On this note, check out this wonderful essay about protecting biodiversity.

Here’s one last video of the jewels of Southeast Asia.

Further reading

1. Orr AG, Charles JK (1994). Foraging in the giant forest ant, Camponotus gigas (Smith)(Hymenoptera: Formicidae): evidence for temporal and spatial specialisation in foraging activity. Journal Natural History, 28:861-872
2. Orr AG, Charles JK, Yahya Hj HR, Sharebini Hj N (1996). Nesting and colony structure in the giant forest ant Camponotus gigas (Latreille) (Hymenoptera: Formicidae). The Raffles Bulletin of Zoology 44:247-251
3. Pfeiffer M, Linsenmair KE (1997). Reproductive synchronization in the tropics: the circa-semiannual rhythm in the nuptial flight of the giant ant Camponotus gigas Latreille (Hym./Form.). Ecotropica, 3:21-32
4. Pfeiffer M, Linsenmair KE (1998). Polydomy and the organization of foraging in a colony of the Malaysian giant ant Camponotus gigas (Hym./Form.). Oecologia, 117:579-590
5. Pfeiffer M, Linsenmair KE (2000). Contributions to the life history of the Malaysian giant ant Camponotus gigas (Hymenoptera / Formicidae). Insectes Sociaux, 47:123-132
6. Pfeiffer M, Linsenmair KE (2001). Territoriality in the Malaysian giant ant Camponotus gigas (Hymenoptera /Formicidae). Journal of Ethology, 19:75-85
7. Pfeiffer, M. A. R. T. I. N., & Linsenmair, K. E. (2007). Trophobiosis in a tropical rainforest on Borneo: Giant ants Camponotus gigas (Hymenoptera: Formicidae) herd wax cicadas Bythopsyrna circulata (Auchenorrhyncha: Flatidae). Asian Myrmecol, 1, 105-119.

 

Have you encountered giant forest ants? What did you observe?  Let us know in the comments section below!

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