Pleistocene Dung Beetles

An odd thought occurred to me the other day involving Hindu reincarnation myths and dung beetles.  I happened to jog past a female rainbow scarab beetle (Phanaeus vintex), rolling a dog turd on the asphalt-topped road.  (Female scarab beetles lack the male’s horn, making the sexes easy to distinguish.)  Scarab beetles bury feces and lay their eggs in it.  Both the adults and larva eat shit.  Apparently, this particular scarab beetle was looking for soft earth where it could bury its offspring’s food supply, but it couldn’t find the end of the hard road–it kept rolling the turd in circles.  I felt sorry for the creature because it would roll the turd within inches of the side of the road, almost to the dirt, then it would turn around and roll it toward the other side.  A car ran over the turd, busting it into 3 pieces.  Undeterred, the dung beetle picked the largest piece left and began rolling it in circles again, never quite reaching the dirt for as long as I observed it.  I’m not familiar with the Hindu religion, but I think they believe human spirits can be reincarnated as animals.  Suppose the Hindu Gods punished a human, whose sin during life was laziness, by reincarnating his soul as a dung beetle stuck rolling a heavy turd on a hard surface where it could never find a soft place to rest.  The soul could spend an eternity of hard labor to make up for his earthly slothfulness.  In reality a dung beetle never gets discouraged because insects are automatons with no emotions.  Before man built hard roads the only environment where dung beetles could become indefinitely trapped rolling turds were large granite outcroppings.  Dung beetles are yet another organism suffering a high death toll because of man’s extensive road network.

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I saw this female rainbow scarab beetle rolling a dog turd on the street in front of my house.  It was aimlessly rolling it around in circles.  It just missed getting run over by cars.  Click to enlarge.

There are 3 types of dung utilization behaviors among the many species of dung beetles.  Some take a piece of shit and roll it some distance away from the manure pile before digging a hole and depositing an egg in it.  These dung beetles are known as “rollers” and include members of the Phanaeus genus.  The “tunnelers,” including members of the Onthophagus genus, dig holes adjacent and under the dung pile where they deposit their eggs.  The “dwellers” live and lay their eggs inside the dung pile.  These include members of the Aphodius genus, and they release chemicals that keep the dung patty moist.

It is likely the widespread extinction of megafauna at the end of the Pleistocene caused a drastic reduction in the abundance and diversity of dung beetles.  One study found that the diversity and size of dung beetle species in Africa was higher in regions with abundant populations of megafauna.  Researchers counted 50 species of dung beetles in savannahs where elephants still occurred, 41 species where just cattle ranged, and 30 species in regions with no large mammals.  Dung beetles that switched to donkey shit in regions where elephants became extirpated were reduced in size.

Most species of extinct Pleistocene dung beetles will likely remain unknown to science because the odds of preservation for insects are even lower than those for large vertebrates.  However, 3 extinct species have been recovered from the La Brea Tar Pits in California–Onthophagus everestae, Copris pristinus, and an unnamed species in the Phanaeus genus.  (It’s possible some of these may be extant but undiscovered, but so far no entomologist has found a living specimen.)  The only species of dung beetle found in a preserved mammoth turd is the still extant Aphodius fossor, a large insect found in cow and horse pastures of Eurasia and North America.  Aphodius fossor probably followed herds of megafauna across the Bering land bridge almost 2 million years ago.  The specimen of mammoth dung containing the sub-fossil dung beetle was recovered from Bechan Cave, Utah.  An excavation at Snowmass, Colorado has yielded the remains of 9 species of dung beetles associated with the bones of megafauna dating to 120,000 years BP-77,000 years BP.  Scientists have identified 3 of the species, and they still occur in the region.  The remains of the other 6 species are too fragmentary to positively identify to the species level, but they may or may not represent extinct beetles.  Dung beetles have yet to be discovered from giant ground sloth dung, but fly larva from the Diptera genus, and a fly pupa from the Scairidae family have been found in sloth shit occasionally preserved in caves.  Flies compete with dung beetles.  Some species of dung beetles have evolved to prey on fly larva they capture inside feces.

Aphodius fossor - David Gould - The Spearwort Fields - 06 July 2014

Aphodius fossor, the only species of dung beetle ever found inside mammoth feces, though without a doubt many species were attracted to piles of megafauna shit during the Pleistocene.  The rarity of manure preservation in the fossil record explains the absence of evidence for other species.

Dung Beetle Life Cycle

Life cycle of a dung beetle roller.  Some other species tunnel into dung and lay their eggs inside the patty.

Dung beetles are beneficial organisms that expedite the recycling of nutrients.  The adults and larva also serve as food for birds and mammalian insectivores.  Birds, moles, shrews, skunks, possums, and armadillos apparently don’t mind the taste of the manure-flavored beetle grubs.

References:

Hanski, Ilkka; and Yues Cambefust

Dung Beetle Ecology

Princeton University Press 2014

Krell, Frank-Thorsten

“Pleistocene Dung Beetles from MIS 5 at Ziegler Reservoir, Snowmass Village, Colorado (Coleoptera: Scarabaedae: Aphodine)”

Denver Museum of Nature and Science Annals 2014

Pierce, W. D.

“Fossil Arthropods of California: Descriptions of Dung Beetles (Scarabidae of the Tar Pits”

Bulletin of Southern California Academy of Science 1946

 

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