Insect Orders (1): Beetles (Coleoptera)
Above: Stenotarsus pardalis, a fine looking fungus beetle that looks like a ladybird (Batesian mimicry at work).
Introduction
Beetles, the most speciose order of animals there is, are known scientifically as Coleoptera, which translates to sheathed wings. This owes to the fact that beetles have hardened fore wings, which are known as elytra (singular: elytron). Indeed, the animals in this diverse group can be found in a wide range of habitats, with a wide array of feeding habits. They come in different shape and sizes, but are all more or less equally fascinating to observe.
Above: Thranius bimaculatus, the baby-faced long-horned beetle, quite common in the secondary forests of Singapore.
Life cycle
Beetles are holometabolous (Endopterygota), meaning that they undergo complete metamorphosis. They share this trait with other insects such as the Lepidopterans (butterflies and moths), Dipterans (flies) and Hymenopterans (ants, sawflies, wasps and bees). Holometabolous insects have juveniles that look nothing like their adult forms. Beetle larvae are commonly known as grubs, and their general appearance includes having no prolegs (unlike caterpillars) and six visible walking legs (unlike many maggots). Many also have relatively large mandibles which they use to chew their food.
Like all Endopterygota, beetle larvae will pupate before transforming into the familiar adults we love (or fear).
Above: A beetle grub found in compost. Seems icky to most humans, but I find it cool!
Below: A ladybird pupa (Illeis koebelei).
Diet
The majority of beetle species derive their food from plants. Many eat leaves, flowers and wood of plants. However, there are many carnivorous ones too that feed on other insects and arthropods. There are even some beetles that feed on decaying matter like dead animals and dung. Their diet varies even among the same family.
Above: A well-fed larva of the leaf beetle Lema pectoralis on its host flower, the bamboo orchid, Arundina graminifolia.
Relationship with humans
Many beetles are considered pests, because of their gregarious herbivorous or saprophagous feeding habits. These beetles damage crops, ornamental plants and furniture. For example, the Mexican bean beetle (Epilachna varivestis) and the Colorado Potato Beetle (Leptinotarsa decemlineata) are pests of crops such as beans and potatoes, respectively. Certain weevils (Sitophilus spp.) feed on stored grains and the larvae of many beetles in the family Anobiidae (the wood-borers) are known to break down wooden furniture.
Conversely, there are a good number of beneficial beetles. Many ladybirds (Coccinellidae) are effective biological control animals that feed on crop pests such as aphids, scale insects and thrips. Ground beetles (Carabidae) and rove beetles (Staphylinidae) are also mainly carnivorous insects that help control certain types of pests. Dung beetles (Scarabaeidae) are very essential in nutrient cycling, and also reduce the numbers of pest flies by robbing them of dung to lay their eggs in.
Beetles are also food for many animals, including humans. For example, the mealworm (Tenebrio molitor), a type of darkling beetle larva, is commonly raised to feed humans, fish and the like. This creature is also known to be able to digest plastics, and as a result has sparked much interest in the scientific community.
Notable beetle families
1) Cerambycidae (Longhorn beetles)
Most are xylophagous, meaning they feed on wood. Many have distinctive long antennae, thus giving them their common names. Notable species found in Singapore include Thranius bimaculatus, Coptops leucostictica, and Cylindrepomus laetus.
2) Scarabaeidae (Scarab beetles)
This huge family consists of many of the more well-known beetles, like the rhinoceros beetle and the dung beetle. The longest beetle in the world, Dynastes hercules, as well as the heaviest insect, Goliathus goliatus, is found in this family. In Singapore, scarab beetles such as the flower chafer, Anomala variegata, are often found flying into homes to seek refuge from wet weather. Other notable species in Singapore include Oryctes rhinoceros (Rhinoceros beetle), Taeniodera monacha and Aprosterma pallide, another common visitor in urban homes.
Above: An unknown scarab beetle chilling on my hand. Based on experience, this species is known to emit a musky odour if disturbed too much.
3) Coccinellidae (Ladybirds)
Perhaps the most liked beetles among typical humans, most ladybirds are ferocious predators of other insects, although herbivorous and fungivorous ones do exist. Many ladybirds have varying patterns on their elytra even among the same species, making it a little difficult to positively identify them in the field. Looking at their pronotum or genitals often provide greater accuracy in their identification. In Singapore, Cheilomenes sexmaculata, Heteroneda reticulata (Netty ladybird), Epilachna indica (a herbivorous ladybird) and Illeis koebelei (a fungus feeder) are some of the more notable ladybirds.
Above: A herbivorous ladybird, Epilachna indica.
4) Curculionidae (True weevils)
All weevils are herbivorous, and many are considered pests. They have a trademark 'snout' which makes them pretty distinguishable from other beetles. Singaporean species include Apoderus notatus (Leaf rolling weevils) and Geotragus inflatus.
5) Chrysomelidae (Leaf beetles)
As their name suggests, all Chrysomlidae are herbivorous and most feed mainly on leaves, although flowers may also be eaten. Lema pectoralis, Aspidomorpha miliaris (Tortoise beetle), Altica cyanea (Flea beetle), and Argopus brevis are just some of the leaf beetles found in Singapore.
Above: A leaf beetle, Lema pectoralis.
6) Staphylinidae (Rove beetles)
This family contains the most described species of any beetle. Most are carnivorous, although herbivorous and detritivorous ones do exist. The southeast asian Paedarus rove beetles are known to cause Paederus Dermatitis, from the secretions of the beetles when they are accidentally crushed or disturbed. Sepedophilus bisignatus is a peculiar looking rove beetle found in Singapore.
7) Carabidae (Ground beetles)
Most are carnivorous. They are extremely fast on their feet, with the tiger beetles being known as possibly the fastest animals on the planet with respect to their body size. In Singapore, Catascopus dalbertisi and Cicindela aurulenta (Spotted tiger beetle) are notable.
8) Tenebrionidae (Darkling beetles)
The most well-known species are probably Zophobas morio (Superworm) and Tenebrio molitor (Mealworm) because the larvae of these two species are commonly sold in aquariums as fish feed. Darkling beetles are mainly nocturnal, and are mostly scavengers, feeding on dead animal or plant matter. Locally, Amarygmus sp. and Derispia sp. can be found.
9) Lampyridae (Fireflies)
Unlike what their common name suggests, fireflies are not flies at all, but beetles instead. Most are carnivorous and the larvae of some species are known as glow worms as they emit light to attract potential prey. Adult fireflies also emit light to attract mates, and the females of some species (like the North American Photuris versicolor) are known to mimic the visual displays of other species in order to kill hapless males of the other species for food. Not all Lampyridae emit light however. In Singapore, the locally endangered Pteroptyx valida (though common in Malaysia and Indonesia) and Lychnuris fumigata can still be found in less disturbed areas.
10) Lycidae (Net-winged beetles)
Famous in Singapore for the neotenous females of certain species, known as the trilobite beetles, Lycidae beetles are predaceous in their larva form, while the adults are known to feed on nectar or do not feed at all. Duliticola hoiseni (Trilobite beetle) and Dictyoptera aurora are two magnificent species found in Singapore.
11) Lucanidae (Stag beetles)
Very rarely seen in Singapore, they feed mostly on decaying wood. Aegus dilatatus is a local species.
12) Erotylidae (Pleasing fungus beetles)
The majority feed on fungus and plant matter, but most have no direct impact on humans. Some beautiful species in Singapore are Episcapha quadrimacula and Micrencaustes lunulata.
13) Endomychidae (Handsome fungus beetles)
Most feed on fungi. The ladybird mimicking beauty in the main picture, Stenotarsus pardalis, along with other notably interesting beetles like Eumorphus spp. and Spathomeles sp. are found in Singapore.
14) Cleridae (Checkered beetles)
Mostly predaceous, some are scavengers or feed on pollen instead. A Singaporean species is Omadius sp.
15) Buprestidae (Jewel beetles)
Most are brightly coloured, and feed on wood. Found in Singapore are Endelus cupido and Chrysobothris discedens.
16) Passalidae (Bess beetles)
Xylophagous, with striated elytra. Leptaulax sp. and Aceraius moeschleri are native species.
17) Dytiscidae (Diving beetles)
Predatory beetles capable of inflicting a painful bite, these aquatic beetles are able to trap air bubbles under their elytra to allow them to survive extended periods of time underwater, where they hunt smaller aquatic organisms like tadpoles and fish. In Singapore, some Dytiscidae include Copelatus andamanicus and Hydrovatus sinister.
Some beetles on Instagram