Fig. 1: (from left to right) Cordyline fruticosa (Goodluck Plant), Koompassia malaccensis (Kempas) and nymphs of Cantao ocellatus (Mallotus Shield Bug)

Last weekend (2 March), I took a short evening walk in the park next to my apartment. I spotted a flowering Cordyline fruticosa (Goodluck Plant), a fruiting Koompassia malaccensis (Kempas), and nymphs of Cantao ocellatus (Mallotus Shield Bug) on a fruiting Mallotus paniculatus (Turn-in-the-wind) (Fig. 1). The most interesting discovery was several small “beetles” on the back of a fern frond (Thelypteris subpubescens). As I did not have my camera, I returned the next day to capture their images.

Fig. 2: Adult and nymph of Monalocoris filicis (Bracken Bug)

Upon examining the enlarged images, it became apparent that the "beetles" were actually bugs. Based on their overall appearance, they appear to be members of the Miridae family, which includes plant bugs, leaf bugs, and grass bugs. The presence of nymphs on the fern alongside the adults (Fig. 2) suggests that this fern is their host plant. A key difference between bugs and beetles lies in their feeding behavior. While both may feed on plant leaves, bugs use their sharp and elongated mouthparts to pierce the leaf surface and extract plant sap. In contrast, beetles chew the leaves. This explains the lack of observable damage on the fern fronds. An online search led to a Taiwan website featuring images of a bug that feeds on ferns, known as Monalocoris filicis (Bracken Bug), which closely matches the observed specimens.

As of 9 March 2025, the iNaturalist website has recorded 197 observations of Monalocoris filicis worldwide. Most observations are from Europe, with fewer records from Japan, China, Taiwan, and Korea. In Southeast Asia, there is only a single observation from Indonesia, which appears to be of a dead specimen.

Fig. 3: Unknown beetle and the damaged frond of Pteris tripartita (Giant Brake)

The bug observed on the fern reminded me of a fern-feeding beetle sighted in July 2023 in another park. It was an unusual large beetle with an orange head and a dark body that initially resembled a wasp Fig. 3:. The host plant was a relatively large fern known as Pteris tripartita (Giant Brake), which is not commonly found in Singapore. Several beetles were feeding on the fronds of the fern. The number of beetles present and the extent of damage to the fronds suggest that this fern is likely a host plant for this species. Fern-feeding beetles are uncommon. The only other fern-feeding beetle I have encountered is a Halticorcus species that feeds on Nephrolepis biserrata (Giant Sword Fern), first observed about five years ago in July 2020.

Fig. 4: Unknow beetle and the damged leave of Dendrophthoe pentandra (Malayan Mistletoe)

Near the end of my photo-taking walk, I observed a few Planchonella obovata (Sea Gutta) with flower buds. This tree is widely planted in parks and along roadsides in Singapore. The few trees in the park are still relatively young and short. On one of the trees, there was a parasitic plant, Dendrophthoe pentandra (Malayan Mistletoe), attached to one of the branches. This species of parasitic plant is very common in my area. I even have one flowering specimen growing on my potted Syzygium polyanthum (Indonesian Bay Leaf) at this moment. While inspecting the Malayan Mistletoe on the Sea Gutta tree, I noticed that its leaves were all significantly damaged, showing signs of being eaten by beetles. Consequently, I began searching for the beetles among the leaves. Shortly thereafter, I located two of them on the surface of the leaves (Fig. 4). In a nearby Cratoxylum cochinchinense (Yellow Cow Wood) tree, I observed similar damage to the leaves of a Malayan Mistletoe high up in the tree.

Thus far, I have been unable to determine the identities of the two unknown beetles that feed on the mistletoe and fern, respectively.