Catharsius molossus (Linnaeus, 1758)
Molossus Dung Beetle
Figure 1: Four adult male Catharsius molossus specimens beside a Singaporean 5 cent coin.
Source: Tiffany Lum (permission obtained)
Overview
Ever seen a shiny black thing rolling a ball of soil on the ground? Behold, the janitors of the forest.
Dung beetles get their name from their diet and use of dung as nesting material. This very act makes them important nutrient recyclers in the ecosystem. Small and unassuming little helpers, they deserve a little more recognition for what they do!
Studies have suggested that there are negative impacts of urbanisation on dung beetle abundance
Interestingly, some nocturnal species of dung beetles that belong to the same family as Catharsius molossus (Scarabaeidae) use the polarized light of the moon to orientate themselves, helping them to move in a straight line.
While studies have only been on the genus Scarabeus, there is no evidence that other nocturnal beetles do not rely on moonlight for navigation too. In light of such news, it is worth considering what effects rapid urbanisation and light pollution can have on the dung beetles. There should also be more research done on dung beetles in Singapore, especially the nocturnal ones like the Molossus Dung Beetle.
Nocturnal
Nocturnal animals are active at night and inactive during the day. The opposite of nocturnal is diurnal.
Figure 2: Adult male Catharsius molossus. Source: Tiffany Lum (permission obtained)
Functional Groups
As you can probably guess, dung beetles get their name from their reliance on animal excrement for food and nesting material. However, different dung beetles ahve different methods of dealing with dung. As such, dung beetles are usually classified into 3 functional or behavioural groups, depending on how they manipulate dung.
1. Rollers (telocoprids). They construct balls from dung, then roll them away, to prepare and bury them for nesting.Namely:
2. Tunnellers (paracoprids). They create almost vertical tunnels by burrowing down directly under the dung. After which they pack a portion of dung to be used for the formation of a brood ball, in which they lay their eggs.
3. Dwellers (endocorprids) live inside or just slightly below the dung source to feed and breed. Dwellers also tend to be smaller than the other 2 functional groups of beetles.
Figure 3: Visual representation of where the different functional groups tend to be in under a dung source.
Source: Goh Yuen Je Charlotte (permission obtained)
The Molossus Dung Beetle (Catharsisus molossus) is a tunneller. Watch this Molossus Dung Beetle tunnel!
This video was filmed in Khao Yai, Phetchaburi, Thailand.
Common Name
Catharsius molossus is commonly known as the Molossus beetle. In Chinese, it is known as 神農蜣螂 (shén nǒng qiāng lǎng).
Distribution
The Molossus Dung Beetle is found across Southeast Asia in India, southern China, Thailand, Vietnam, Indonesia and most recently, again in Singapore.
In Singapore, it was previously thought to be locally extinct after a census done in 2009 at the Bukit Timah Nature Reserve had no specimens.
The study had found 48 Catharsius molossus specimens in CCNR and 1 in BTNR. Out of those found in CCNR, 20 were found in primary forest sites and 28 in secondary forest site (Figure 3). The sole specimen from BTNR was found in a secondary forest site. This suggests that the Molossus dung beetle is able to persist in both secondary and primary forest sites
Figure 4: Location, type of bait and number of Catharsius molossus specimens caught are shown in this diagram.
We see a strong preference for cattle dung. Source: Ong Xin Rui (permission pending). Modified by Goh Yuen Je Charlotte.
The study also revealed that the Molossus Dung Beetle has a strong preference for using herbivore dung. In Singapore, the most likely source of herbivore dung comes from the Sambar deers and Eurasian wild boars as they are the largest mammals with establish populations in our forests. Hence, the rediscovery and local distribution of the Molossus Dung Beetle could be tied to the distribution and proliferation of the these large herbivores!
Singapore's forest can be differentiated into primary and secondary forests: Primary forests are forested areas that have never been disturbed by human activity like logging and agriculture. On the other hand, secondary forests are forested areas that have been previously cut and regrown. However, some secondary forest sites in Singapore may be less disturbed by humans as compared to primary forest sites that are frequently visited by humans.
Significance
Ecological Role
Dung beetles provide important ecosystem services for maintaing the health of forest ecosystems. Dung beetles play an especially important role in soil aeration, soil fertilisation, enhancing plant growth and secondary seed dispersal. This is attributed to their removal, procession and burial of dung.
Nutrient Cycling
The dung of larger vertebrate animals contain a significant amount of nutrients like nitrogen, which is also often the limiting factor for plant growth and productivity
Thus, by removing, processing and burying the dung of these animals, dung beetles not only help turnover and aerate the soil but also help fertilise the soil. Tunneller dung beetles, like C. molossus also help fertilise the soil by packing nurtient-rich dung into the deeper soil layers. They are especially important for soil aeration and maintaing water porosity as they bring deeper layers of soil up to the surface during their nesting behavior
Secondary seed dispersal
Seeds are often found undigested in the faeces of primary seed dispersers like the Sambar deer (Rusa unicolor) and the Eurasian wild boar (Sus scrofa). Both of which have established known populations in Singapore's Central Catchment Nature Reserve (CCNR) and Bukit Timah Nature Reserve (BTNR).
Figure 5 : Adult and juvenile Eurasian wild boars (Sus scrofa). Source: WildSingapore (permission obtained)
As the competition for dung can get intense for some of these beetles in the wild, stealing of dung balls and brood balls are a common occurance. It's a tough life for these dung beetles!
As the largest known tunneller dung beetle, Catharsisus molossus plays an important role as secondary seed disperser.
predation and germination. Journal of Tropical Ecology. 14, 199–215]]>
an their implications for natural and managed systems. Annual Review of Ecology and Systematics.
25,263–292.]]>
Pest Control
Interestingly, dung beetles can also help with parasite control through their adult and larval feeding and nesting activity. Dung beetles are able to control the abundance of flies, nematodes and microorganisms that feed on decaying organic materials and blood. Certain studies have show that it could be related to the grinding action of dung beetles during feeding. However, the specific mechanism and reason behind dung beetle's ability for parasite suppression is still poorly understood. This could perhaps be due to the sheer amount of unknowns regarding dung beetle behaviour.
While there have been concerns regarding dung beetles as carriers of certain parasites and pathogens, there has not been concrete evidence proving otherwise. Thankfully, Molossus Dung Beetles are proven to not be carriers of E. coli, a bacteria found in animal and human excrement that can cause several diseases like pneumonia and diarrhea.
Medicinal Use
The Molossus Dung Beetle is widely used in Traditional Chinese Medicine (TCM). An extract of C. molossus is often used in the submerged fermentation of a medicinal fungus called "Ling Zhi" (Ganoderma lucidum) also commonly used in TCM to treat various human diseases like gastritis, hepatitis, chronic bronchitis and immunological disorders.
Figure 6: Ling zhi fungus (Ganoderma lucidum). Source: Wikimedia (Creative Commons attribution liscense)
Diagnostics & Morphology
Diagnostic characters: Black, broadly oval, very convex and opaque. They have broad heads and clypeus with ocular lobes densely and coarsely granular with a small smooth shining area adjoining inner margin of each eye (See Figure 10 and 11). Pronotum densely granulate with a sharp declivity in front and upper surface of which forms a sharp ridge feebly convex in middle and curved with its extremities. Males having a conical median horn with broad and flattened base and short pointed tip, while female bears a short pointed process.
Confusion:
There is a chance that the Molossus Dung Beetle may be mistaken for a Coconut rhinoceros beetle (Orcytes rhinoceros), a large stag beetle found in Singapore. The Molossus Dung Beetle can be distinguished by it more oval-shaped body as compared to the Coconut rhinoceros beetle which has a longer body.
Figure 7 : Lateral view of a male Coconut rhinoceros beetle (Orcytes rhinoceros). Source: Tiffany Lum (permission obtained)
Figure 8: Lateral view of a major male Catharsisus molossus. Source: Tiffany Lum (permission obtained)
Larval and Egg
The larval form and eggs of the Molossus Dung Beetle have not yet been documented. This is likely due to the difficulty of rearing them in laboratories. In the wild it could also be difficult to find them as Molossus Dung Beetles are tunnellers, hence the brood balls are usually buried deep in the ground and are tough to sieve out. However, there is a description for Scarabaeinae sub-family larvae
Figure 9: Larva of Onthophagus babirussa in dung. Source: Tiffany Lum (permission obtained)
Adult
Adult dung beetles have modified mouth parts which are adapted to feeding on dung. The clypeus is expanded and covers the mouth parts. The elytra, which cover the wings, expose the pygidium. They also have a space between their middle legs to allow for manipulation of the dung.
Adult Molossus Dung Beetles are usually 25.0 – 45.0 mm in length, with elongate-oval and black bodies. The clypeus (part of head anterior to the frons) is broadly rounded. The pronotum is densely granulate with a sharp declivity in front and upper surface of which forms a sharp ridge feebly convex in middle and curved with its extremities. In both males and females, the frons (part of the head in between the eyes) do not have horns or tubercles, and the pronotum has well-developed tumosity (bump-like) and distinct horizontal ridge. They have a hardened and chitinous wing-cover called the elytra. On the elytra there are indistinct longitudinal lines called striae (iNaturalist, n.d). Only males have horns on their clypeus.
Figure 10: Dorsal view of a male Catharsius molossus. Source: Tiffany Lum (permission obtained). Annotated by Goh Yuen Je Charlotte.
Figure 11: Lateral view of a major male Catharsisus molossus. Source: Tiffany Lum (permission obtained). Annotated by Goh Yuen Je Charlotte.
Figure 12: Four specimens of Catharsius spp. besides a Singaporean 5 cent coin (16.75mm)
Sexual Dimorphism
Catharsisus molossus exhibits sexual dimorphism where the male and female adult beetles have distinctly different physical traits. Males often have a conical median horn with broad and flattened base and short pointed tip on the clypeal, while females bear short point tips or not at all. The horns on males are important in their mating and courtship behaviour. Interestingly, there are two distinct morphological male types with different horn size. Major males have distinct horns on the clypeal but in minor males, these are reduced or lacking.
Below we see the comparison of the female (Figure 13) and male Molossus Dung Beetle (Figure 14).
Figure 13: Lateral view of female Catharsisus molossus. Scale bar reads 5mm. Source: E.L Engasser (permission pending)
Figure 14: Lateral view of Major male Catharsisus molossus. Scale bar reads 5mm. Source: E.L Engasser (permission pending)
Next, we have the side-by-side comparision of the Minor male with smaller and less pronouced horns (Figure 15) and Major male with the larger and more pronouced horns (Figure 14) below. Look at the clear difference in the size and prescence of horns!
Figure 15: Lateral view of Minor male Catharsisus molossus. Scale bar reads 5mm. Source: E.L Engasser (permission pending)
Figure 14: Lateral view of Major male Catharsisus molossus. Scale bar reads 5mm.Source: E.L Engasser (permission pending)
Biology
Life History & General behaviour
The Molossus Dung Beetle has a four-stage life cycle, comprising of egg, larva, pupa and adult stages. Like other beetle in the tribe Corprini, the Molossus Dung Beetle is nocturnal. This means that it is most active nesting, feeding and mating and engaging in other activities at night.
Nesting Behaviour
Adult dung beetles usually dung into balls called brood balls, into which females lay their eggs. For Catharsius spp., both females and males contribute to the work for the creation of nesting material and digging to establish the nesting site.
In Catharsius spp. the brood balls are divided into several brood ovoids, each with one egg each. Parents also do not tend to broods while they develop.
Feeding behaviour:
The Molossus Dung Beetle, like other dung beetles are coprophagous. This means they feed on the fecal matter of other large mammals and for C. molossus, both adults and larvae feed on dung. Interestingly, recent discovery has shown that the Molossus Dung Beetle appears to be a specialist of herbivores’ dung.
Taxonomy and Systematics
Classification
Kingdom: | Animalia |
Phylum: | Arthropoda |
| Class: | Insecta |
Order: | Coleoptera |
Family: | Scarabaeidae |
Subfamily: | Scarabaeinae (Latreille, 1802) |
Tribe: | Coprini |
Genus: | Catharsius |
| Species: | Catharsius molossus (Linnaeus, 1758) |
Etymology
Linneus first described it as Scarabaeus molossus in 1758. The genus epithet, Scarabaeus, comes from New Latin, meaning “sacred scarab beetle”
The species epithet molossus comes from New Latin, which was the name of an ancient breed of Mastiff dog: the Molossian hound or the molossus
Original species description
C. molossus was first described by Linneaeus in 1758 under Scarabaeus molossus.
Figure 16 : Original species description of Catharsius molossus by Linneaus from Systema Naturae
Type
There were no holotypes designated when Linnaeus first described the species in 1758 as there were no type specimens. Later on, two neotypes used to describe C. molossus by Biswas & Chatterjee in Zoological Survey of India, Calcutta in 1986. The neotypes were obtained from Kerala, Silent Valley in 1980. There is no information on where and if these neotypes were preserved.
In Singapore, the reference specimens can be found in the Zoological Reference Collection of the Raffles Museum of Biodiversity Research, National University of Singapore.
Synonomy
| Synonyms | Author, Year |
|---|---|
Catharsius borneensis | Paulian, 1936 |
| Catharsius dubius | Paulian, 1936 |
| Catharsius kangeanus | Paulian, 1936 |
| Catharsius timorensis | Lansberge, 1879 |
| Copris urus | Fabricius, 1801 |
| Scarabaeus abbreviatus | Herbst, 1789 |
| Scarabaeus berbiceus | Herbst, 1789 |
| Scarabaeus janus | Olivier, 1789 |
| Scarabaeus molossus | Linnaeus, 1758 |
Phylogeny
Early classifications of tribes under Scarabaeinae were based on the assumption that the evolution of dung beetles involved solely on rolling or tunnelling behavior and associated morphological modifications. This suggests that the definition of species could be based on ecological and biological species concept. Such categorisation of dung beetles may have little phylogenetic validity as there were evidence polyphyly and of tunneller groups nested within the rollers.
Figure 17: Bayesian 7-partition analysis was done and the posterior probability values are below branches leading to the node. Posterior probability is a conditional probability that is assigned after the relevant background is taken into account.
Figure 18 : Magnified version on the tree in figure 17 . The tunneller and roller groups are indicated on the tree. The position of Catharsius molossus is also shown in a red box with posterior probabilty of 1.0. Annotated by Goh Yuen Je Charlotte in red.
Figure 19 : Zoomed in version of the tree in figure 17. The tribe Coprini is clearly polyphylectic.
Annotated by Goh Yuen Je Charlotte in red.
In 2007, Monaghan et al.
the Scarabaeinae (dung beetles). Molecular Phylogenetics and Evolution, 45(2), 674-692.
doi:10.1016/j.ympev.2007.06.009
After considering the other methods, Bayesian 7-partition analysis was done. The posterior probability value for Catharsius molassusis displayed is 1.0, indicating that it is a well-supported node. The posterior probability value for Catharsius/Metacartharsius is also 1.0, suggesting good support for monophyly. The analysis by Monaghan et al.
the Scarabaeinae (dung beetles). Molecular Phylogenetics and Evolution, 45(2), 674-692.
doi:10.1016/j.ympev.2007.06.009
Additionally, in Figure 18 we see that clade G actually has both rollers (Gymnopleurini) and tunnellers (Coprini), showing evidence of nesting. The Coprini tribe to which C. molossus belongs to was found to be polyphylectic as evident in Figure 19. Other tribes like Oniticellini seem to be poorly supported here as well as seen in Figure 19.
Thus, there is need for more studies to be done, perhaps using different genes and including different methods of analysis like maximum parsimony. Until there is consensus, cladograms cannot be used for classification or to tell evolutionary history.
Conservation Message
Insects are often the most unassuming of animals. However, if you stop and take a closer look, you’d often be surprised at what the insect world has to show!
While we may rejoice over the rediscovery of the Molossus dung beetle in our Nature reserves. There is still much more left to be done to ensure that a viable population remains. Considering their ecological significance, there should be more attention given to studying the life histories and ecologies of dung beetles like the Molossus Dungg Beetle.Besides more in-depth studies, we should also keep in mind the effects of human development and urbanisation on these insects. Dung beetles, especially nocturnal ones like the Molossus dung beetle can be negatively affected by the resultant light pollution from increasing urbanisation. Most recently, in light of the Mandai Development project that fringes the CCNR, more attention should be should be directed on assessing the impacts on nocturnal fauna communities.
Figure 20: Female C. molossus looking like it's waving good bye! Source: Tiffany Lum (permission obtained)
References
This page was authored by Goh Yuen Je Charlotte
Last curated on 10/12/2018
