Fig. 1: Potted plants at the balcony area within my home showered by the golden morning sun

There are 24 small pots of similar size arranged in a straight line along the balcony inside my home (Fig. 1). Each pot has a diameter of 26 centimetres at the top and a height of 20 centimetres. They are placed on a chest-level extended edge of the balcony, which is equipped with window grills to prevent them from falling off.

To maintain a natural ecosystem within the pots, I have allowed small organisms found in the soil to reproduce and move freely among the pots. All these organisms play a role in the decomposition process. Due to the limited food sources within the pots, I have placed unwanted fruit leftovers on the soil for their consumption. To aid in the decomposition process, I cut the fruit remains into smaller pieces. Among the fruit remains, papaya skin has proven to be the most effective, as it is typically fully consumed within a week. Conversely, banana skin tends to blacken and harden within a few days, rendering it unappealing to the decomposing organisms.

Fig. 2: Round-backed millipedes (family: Pseudospirobolellidae)

These creatures enter the pots possibly through the soil or plants that were introduced. There is a colony of small dark-orange ants, (Pheidole parva), that has been living in the pots for many years. Their population changes based on the availability of food sources. Another member of the community is the Miniature Awlsnail (Subulina octona), a small snail with a yellowish elongated tower-like shell. The third member is a long-flange millipede, Orthomorpha coarctata. These three are active at any time of the day. Another millipede, likely from the family Pseudospirobolellidae (Round-backed millipedes), is more elusive and only becomes active at night (Fig. 2). In Singapore, two species from this family have been reported [1]. Except for the ants, the other creatures prefer to remain at the soil level and do not climb onto the plants.

Fig. 4: Mushrooms (Coprinellus species) emerging from the rabbit dung

A few weeks ago, I began utilizing rabbit dung as fertilizer for my plants. This resource is readily available since a pet rabbit has recently become part of my household. Rabbit dung is characterized by its small cylindrical shape, relative firmness, and lack of odour. It serves as nourishment for the long-flange millipede and the Miniature Awlsnail, which have been observed feeding on these dung pellets. The primary consumers, however, are the earthworms. These particular earthworms are not the larger variants commonly found in gardens but rather a smaller species.

Fig. 3: Earthworm escaping to the surface when the soil is too wet

Earthworms are a relatively understudied group in Singapore, with the most recent research publication dating back to 2005 [2], recording 19 species of terrestrial earthworms. They exhibit a preference for moist soil conditions as opposed to excessively wet environments. Observations indicate that they migrate to the soil surface during heavy rainfall when the soil becomes saturated (Fig. 3). Consequently, careful moderation of watering practices is required to maintain their optimal living conditions.

While millipedes and snails operate predominantly on the soil surface, earthworms engage with the dung pellets from below. Collectively, these organisms exhibit high efficiency in decomposing the dung within an average of two to three days. Although numerous other microorganisms contribute to this ecosystem, many are too minute to be observed directly. Overall, the various species within this micro-ecosystem appear to coexist harmoniously.

Recent cooler temperatures have caused small mushrooms, likely Coprinellus species (Fig. 4), to sprout from the dung balls. These mushrooms appear in the late evening and disintegrate by morning when exposed to sunlight. The addition of rabbit dung and facilitated decomposition by active organisms in the pots have significantly improved plant health compared to earlier periods without this booster.

References:

[1] Decker P. Annotated checklist of the millipedes (Diplopoda) and centipedes (Chilopoda) of Singapore. Raffles Museum of Biodiversity Research 2013. | Read article |

[2] Shen HP, Yeo DCJ. Terrestrial earthworms (Oligochaeta) from Singapore. The Raffles Bulletin of Zoology 2005;53(1):13-33. | Read article |