9 April 2017 | Cocoa Black Ant | Dolichoderus thoracicus |
This ant (Dolichoderus thoracicus) had been a special guest, though uninvited at my potted area since June 2015. Its common name Cocoa Black Ant probably came from its affiliation to the Cocoa Tree (Theobroma cacao). Indeed, studies had showed that it might reduce damages to cocoa fruits by driving away the Cocoa Mirid Bug (Helopeltis theivora) [1-2]. The ant typically operates in large population. It was the dominant ant in a nearby park until around March 2016, in which it disappeared without a trace from the park. It does bite but it is less fearsome than two other more ferocious ants, Weaver Ant (Oecophylla smaragdina) and Asian Army Ant (Pheidologeton diversus), which are also common dwellers in parks or wild places. Cocoa Black Ant preferred to stay above the ground except during migration. They are dairy farmers where their herds included scale insects, aphids, mealy bugs and nymphs of treehoppers and instead of milk, they are after the sugary secretion from these bugs.
At my balcony area, this ant roams freely among the potted plants and rarely venture out of its territory. Most of the time, they were glued to the abundant scale insects that lined the stem of the Cow Pea or Phasey Bean (Macroptilium lathyroides). Occasionally, they moved across to different pots but always to look after the scale insects or any sugary liquid secreting bugs on those plants. After observing them for more than a year now, I had not seen a single nest. They just stayed with their bug friends day and night. Sometimes, a group of them would gather closely under the leaves.
The Cow Pea in my pots had a longer history. I had already shared a few posts on it (as listed below). Once upon a time, the pea plants were infested with white mealy bugs which eventually killed most of the plants. After the ants (Nylanderia species) that linked to this mealy bugs were chased out by the Cocoa Black Ant, the mealy bugs disappeared and replacing them were the scale insects. The Cow Pea appeared to tolerate the scale insects relatively well, at least for now.
Last Monday, I read a news article in TODAY regarding ant-keeping hobby in Singapore. The article mentioned a Facebook group (Ants Community Singapore) that shared this interest locally. I eagerly visited the Facebook page of this public group and did find some good and interesting information on the ants available here.
 Khoo KC, Ho CT. The influence of Dolichoderus thoracicus (Hymenoptera: Formicidae) on losses due to Helopeltis theivora (Heteroptera: Miridae), black pod disease, and mammalian pests in cocoa in Malaysia. Bulletin of Entomological Research 1992;82(4):485-491. | Abstract |
 Ho CT, Khoo KC. Partners in biological control of cocoa pests: Mutualism between Dolichoderus thoracicus (Hymenoptera: Formicidae) and Cataenococcus hispidus (Hemiptera: Pseudococcidae). Bull Entomol Res 1997;87:461-470. | Read article |