Ground-dwelling beetles

66-0mya Cenozoic Era

Soil Survival Plants Grass-Herbivore symbiosis Soil animals Ground beetles

Scarab beetles

Dung Beetles

While their diversity of around 5,300 species is comparatively modest among beetles, their dung-processing activity makes them one of the most important groups of insects, both ecologically and economically" (Nichols et al 2008)

Triple co-evolution

“Dung beetles use the dung of herbivores, particularly large mammals, to provision their underground nests in which they construct brood balls where the egg is laid. These insects are usually linked to grass-dominated habitats inhabited by abundant and large mammals, which, feeding on grasses, produce large amounts of the insects' food: dung. Fossil brood balls of dung beetles, included in the ichnogenus Coprinisphaera, are typical trace fossils of Southern South American Cenozoic palaeosols ….in a sequence of the middle Eocene-lower Miocene" (Sanchez et al 2010)

This fits incredibly closely with the predicted origins of herbivorous mammals consuming grass at the same time in South America. So the great co-evolution is not just between the famous two herbivores and grass, but another group of organisms. This great triple co-evolution, the grass, the herbivore and the dung beetle, was distributed across the other continents, together.

When did dung beetles appear?

We saw that dung beetles probably originated eating dinosaur dung. There is also evidence of dung beetle fossils from around around 60 mya (Paleocene epoch). At that time, they were present in what is now Europe, North America, and Asia. It is believed that the spread of dung beetles was facilitated by the migration of large mammals, which provided a source of dung for the beetles to feed on.

Dung beetles on elephant dung

Guess what? There is a big debate over exactly when dung beetles evolved, whether dung beetles always have been in association with mammals, or whether dinosaurs were involved early in their history. It is called: Gondwana v ‘Out-of Africa’. The ‘Gondwana theory’ puts their origins in the around 100mya (Cretaceous period) - before Gondwana split up - which is where they are here on tis site. The ‘Out-of-Africa’ puts their origins later, after Gondwana split, in this Cenozoic era and in Africa (Sole & Scholtz 2010). From there they have distributed across the world.

Clear as..

To try to answer this burning question one study was made, who’s “results support the hypothesis of an old age for Scarabaeinae and Gondwanan origin but remain ambiguous about the exact relation of range on lineage diversification…would support the hypothesis that access to new areas was associated with a rise of diversification rates in dung beetles" (Schwery & O'Meara 2021). Hmm, clear as ..dung.

From dung to poo

Dung beetle larvae primarily eat dung, just like the adult beetles.. Once the eggs hatch, the larvae feed on the dung around them, which provides a rich source of nutrients, such as nitrogen, proteins, essential for their growth and development.

After dung beetles digest the dung, they absorb the nutrients and expel waste that is much lower in organic material and nutrients. Their poo is primarily composed of undigestible fibers, minerals, and other materials that they can't absorb, and it lacks the richer organic content of the original dung.

dung beetle larvae

The microbial community in dung beetle poo is different from the dung they eat, as many of the original microbes are either killed during digestion or are replaced by other bacteria that thrive in the beetle's gut environment.

Larval food

"Our results reveal a striking degree of flexibility in the dynamics and timing of larval development in Onthophagus taurus. They also suggest that premature exhaustion of a larva's food supply can serve as a cue for the initiation of metamorphosis. " (Schaffiei et al 2001)

Burying beetles

Fossil evidence of Silphidae suggests carrion beetles existed around 99mya, but no direct fossils of are known from that period. Based on molecular clock analyses, suggest that genus Nicrophorus (sexton beetles) likely diverged from other carrion beetles in this later period, round 66 - 23 mya (Paleogene).. This places the origin of sexton beetles shortly after the mass extinction event that wiped out the non-avian dinosaurs, a time when many new ecological niches became available. The evolution of mammals after this event likely provided more small vertebrate carcasses for these beetles to exploit, facilitating their diversification.

Nicrophorus
Sexton beetle

Cockchafers

Cockchafers are scarabs related with dung beetles and goliath beetles. The specific genus and species that we recognize as cockchafers today (genus Melolontha) likely evolved after the extinction of dinosaurs. Therefore, cockchafers and their close relatives within Scarabaeidae evolved after the period, when flowering plants (angiosperms) emerged but when they were expanding providing new ecological opportunities for herbivorous beetles like scarabs.

Chafer chants

They do not go quietly. We thought soil was silent. But someone has listened in to chafer grubs and learned to distinguish between the larvae of the two white grub species — the common cockchafer (Melolonthamelolontha) and the forest cockchafer (M. hippocastani). Apparently, they buzz in a way that’s similar to the aboveground singing, or stridulation, of cicadas and grasshoppers.

The larvae do this by rubbing their mandibles together. “One could say they grind their teeth to talk to each other underground,” Görres says. “The beauty about stridulations is that they seem to be species-specific, just like bird songs.” Once the larvae pupate, they switch to another noisemaking mechanism, rotating their abdomen within their shell and banging it against the shell wall. She calls it underground twitter. She noticed that a larva kept on its own rarely stridulated. But if more than one shared a container, they sang — a lot. A trio of cockchafer larvae stridulated a total of 682 times during their first two and one-half hours together (Gorres and Chesmore, 2019).

A scarab beetle that also causes crop damage is the larvae of cockchafers known as "white grubs" or "chafer grubs". They hatch after four to six weeks and feed on plant roots, for instance potato roots. The grubs develop in the earth for three to four years, in colder climates even five years, and grow continually to a size of about 4–5 cm, before they pupate in early autumn and develop into an adult cockchafer in six weeks.

Birds, particularly of the crow family (jays, magpies, rooks and crows), badgers and foxes tear up turf in order to access the grubs to feed on them. This shows again, that while we see these graubs as pests, they help build the nutrition bridge from deep soil to land surface

Ground beetles (Carabids)

I believe ground beetles are a good indicator of soil health, as I explained on BBC Gardeners World 2017. However, when I had trapped 4 or 5 in a glass jar overnight, several escaped the jar before the cameras could get there. Ground and diving beetles are common everywhere and are good indicators of healthy soil because they depend on earthworms, slugs, butterffly larvae, woodlice and springtails to feed on (Jelaska et al 2014).

“Ground beetles (Carabidae) are increasingly used as ecological indicators in studies regarding land use because they are ubiquitous, respond quickly to environmental change, have a well-understood taxonomy, and can be trapped with ease"

Walking jewels

Carabid ground beetles, sometimes called "walking jewels", are among the most thoroughly investigated insects in the world.

“Comprehensive analyses using mitochondrial DNA-based dating suggest that carabid diversification took place about 40 to 50 million years ago as an explosive radiation of the major genera, coinciding with the collision of the Indian subcontinent and Eurasian land mass. The analyses also lead to surprising conclusions suggesting discontinuous evolution and parallel morphological evolution". Explanation here..

Typically they lay eggs in the soil or in accumulations of organic matter. Their larvae which are elongate, relatively soft-bodied and have three pairs of legs near the head end typically run round on the surface under leaves. The head, thorax and usually some of the abdominal segments of larvae are often brown or black but the underside is creamy white. The larvae generally remain in the soil or leaf litter, where they feed on other invertebrates and their eggs. As adult beetles, they are much more active and may be seen running over the soil surface.

Sucking springtails

Ground beetles, now running round in the litter will eat ants and springtails by spitting at them, dissolving them, then sucking up their remains (Jaloszynski & Olszanowski 2015) However, collembolans are no easy prey. Surface dwelling springtails can use their tail-like appendages (furca) to fling themselves into the air. Perhaps they use it to escape predators, although I believe it's original function was to spring along water films. Several morphological specialisations for capturing collembolans have evolved in different arthropod groups.

Some like Notiophilus are very specialised collemboland feeders

“Collembola are an important potential food source for carnivorous arthropods living on the soil surface. Nevertheless, due to their effective evasive manoeuvres, Collembola are not an easy prey. Several carabid groups, however, have evolved morphological specialisations to overcome this otherwise effective defence strategy. The adaptive value of this specialisation is still unclear, since some generalist carabids also consume collembolans." (Baulechner et al 2021)

Rove Beetles

The rove beetle tribe Staphylinini comes from one stock producing a lineage of over 5500 relatively large and charismatic species. We saw their origins about 200 may, with diversification of Staphylinini after that showing up in a diverse assemblage of compression fossils in of Early Cretaceous deposits (145-100mya) (Brunke et al 2015). But after that they dispersed widely, and it seems due - not to the asteroid itself but the ensuing temperate changes.

Like the warm

It seems that they flourished in the warmer early Cenozoic but didn’t like the cold They were present in the - then Arctic region, which was tropical, That community is known widely as the ‘boreotropics’,and was a unique mixture of frost-intolerant groups such as palms. However as the planet cooled, this moved towards the Tropics to make it what we know today.

Thermophilic lineages.

"We integrated evidence from Eocene (56-33mya) fossils, distributional and climate data, paleoclimate, paleogeography, and phylogenetic divergence dating to show that intercontinental dispersal of Bolitogyrus ceased in the early Eocene, consistent with the termination of conditions required by thermophilic lineages. These results provide new insight into the poorly known and short-lived Arctic forest community of the Early Eocene and its surviving lineages". (Brunke et al 2017)

Staphylinids are particularlry good soil health indicators as their diversity may representative the whole biodiversity of a single ecosystem. These beetles occupy numerous niches related not only to the soil and the vegetation but also to the diversity of other arthropods and mammals.

Refugia

The Eocene-Oligocene Transition(EOT) 34mya changed the fauna of northern Europe dramatically and rapidly, and nearly half (45.5%) of all beetle genera described from Baltic amber (34-38mya) went extinct globally or they escaped to ‘refugia' (Brunke et al 2019) Could their 'refugio' have been grass?

Staphylinids occur in nearly all ecosystems of the world, from the Arctic to the tropics. Their morphology seems to be highly uniform with short elytra and long body. You’ll see them running fast when disturbed. Their body is flexible so they can inhabit an enormous variety of microhabitats. No other group of beetles has been so successful in living in such an enormous number of diverse habitats, although they do have affinity to certain microhabitats.

Most are found on the soil surface. Rove beetles are unusual beetles in that they live together with a large variety of mammals, birds, and social insects - particularly, ants, bees and termites. For some hosts, the rove beetle guests have beneficial effects, like feeding on their waste products, but for others, they are harmful, when feeding on their eggs, larvae, adults, or stored food (Irmler et al 2018)

Oribatid food

A staphylinid beetle called Scydmaenus feeds mostly on oribatid Scheloribatidae (60+ of prey) "Observations revealed that mechanisms for overcoming the prey’s defences depended on the body form of the mite. When attacking oribatids, with long and spiny legs, the beetles cut off one or two legs before killing the mite by inserting one mandible into its gnathosomal opening" ((Jaloszynski & Olszanowski 2015))

Scydmaenus demolishing an oribatid

various oribatids with beetle damage

The rove beetle Bolitogyrus Chevrolat is remarkable for its 78 living specvies which are microhabitat specialists of fungus-covered deadwood. This map shows their distribution and how they like warmer temperatures. (Brunke 2022)

Termite-chomping rove beetles emerged about 100 mya

Elaterids

These include 'click' beetles who have been around since 250-200 mya (Triassic) but now had a vast new environment. Their larvae are known as ''wireworms'. Grasslands provided an optimal environment because the soil is undisturbed for years and this preserves their natural habitat. They can do substantial damage. They also had a new prey - birds.

dead spots due to wireworm

Increasing beetle larvae were providing food sources for birds

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