Biology of the Dung Beetle
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Like their name implies, Dung Beetles like dung – they are Coprophagous(dung eating) insects.
The term Dung Beetle actually encompasses many different of species of beetle
that use dung(roughly 8000).(1) As a group Dung Beetles are found on all
continents except Antarctica and occur in a variety of environments.(1)(2) It
is thought that Dung Beetles are relatively new species, at most about 40
million years old.(2) As a fun fact: In south America there have been Fossilized
dung balls the size of tennis balls found that date to roughly 30 million years
ago – these Beetles fed on the poop of Mega Fauna(huge mammals) that lived
there.(3)
Today Dung Beetles formally fall within the class Insecta, Order Coleoptera(Beetles), family Scarabaeidae.(4) Dung Beetle species can vary greatly in size(.5 inches to 2.5 inches long) and lifespan(1 month to 3 years or more).(1) Like all Insecta their bodies are divided into 3 parts, head, thorax and abdomen, have three pairs of legs and an exoskeleton surrounds their exterior. Their bodies vary from oval to elongated and they are often brown or black(for example the Scarabaeus sacer) but some species are brightly colored(example the Rainbow Scarab or Phanaeus vindex is a bright green and yellow), they may or may not have horns.(7)(9)
While the specific life cycle and preferred poop of Dung Beetles vary depending upon the species, all reproduce through sexual reproduction where a male and female mate during which the male passes sperm to the female and sometime later the female lays eggs in dung.(1)(5) After the eggs hatch, a larva emerges which feeds on the poop which surrounds it.(8) Eventually the larva enters the pupa stage which is when it undergoes complete metamorphosis and emerges as an adult dung beetle we know and love.(8) It then heads out in search of dung(most Dung beetles are able to fly and use smell to locate dung) to eat and mate.(10)
Today Dung Beetles formally fall within the class Insecta, Order Coleoptera(Beetles), family Scarabaeidae.(4) Dung Beetle species can vary greatly in size(.5 inches to 2.5 inches long) and lifespan(1 month to 3 years or more).(1) Like all Insecta their bodies are divided into 3 parts, head, thorax and abdomen, have three pairs of legs and an exoskeleton surrounds their exterior. Their bodies vary from oval to elongated and they are often brown or black(for example the Scarabaeus sacer) but some species are brightly colored(example the Rainbow Scarab or Phanaeus vindex is a bright green and yellow), they may or may not have horns.(7)(9)
While the specific life cycle and preferred poop of Dung Beetles vary depending upon the species, all reproduce through sexual reproduction where a male and female mate during which the male passes sperm to the female and sometime later the female lays eggs in dung.(1)(5) After the eggs hatch, a larva emerges which feeds on the poop which surrounds it.(8) Eventually the larva enters the pupa stage which is when it undergoes complete metamorphosis and emerges as an adult dung beetle we know and love.(8) It then heads out in search of dung(most Dung beetles are able to fly and use smell to locate dung) to eat and mate.(10)
Dung Beetles can be divided into four groups based upon what
they do with Dung. These group are Rollers (endocoprids), Tunnelers
(paracoprids), Dwellers (telocoprids) and Parasitic (kleptoparasites). Each
group is particularly well suited to the way it interacts with dung.(2)(3) It
is thought these groups evolutionary differences are a result of the need to
protect their resources(or in the case of the kleptoparasitic beetles – steal
resources) from other beetles.(10)
Dwellers
Dwellers or telocoprids don’t roll their dung into balls to
eat later or bury them bellow the dung pat. They just dive right into a fresh
dropping and eat. They also use the dung pat as a nesting site and lay their
eggs directly in the pat itself. Dwellers are typically smaller than the other
two groups. They are also the group that is under the most competition for
resources as they cannot horde their prize like the Tunnelers or Rollers. The
group that constitutes most of the dwellers is the genus Aphodius(which has
over 1,650 species within it!) contained
within the family Scarabaeidae. Most species in the Aphodius genus live in
temperate climates and their preferred food is Bovine(cow) dung. Most species
have one generation per year but the females have relatively high fecundity(the
ability to produce offspring in large numbers), the females laying 100 eggs or
more(which are usually spread out among different dung pats) though their
lifespan(which is usually short, for example the adult lifespan of the Aphodius elegans is 1 month).(10)
Tunnelers
Tunnelers or paracoprids, dig into a dung pat and create a nest bellow the pat itself. Tunnelers use these nests for both food storage/eating and for breeding purposes. The two groups that make up most of the Tunneler populations are the families Geotrypinae and Coprinae within the family Scarabaeidae.
Unlike Rollers who can immediately start construction of their dung ball, when a Tunneler reaches a dung pat it must excavate a burrow before gathering dung. During mating in most species of Tunnelers the male takes the secondary role and the female is the one who does most of the work in excavating the burrow and stocking it with dung. The burrows of these Tunnelers vary from simple to complex where each brood ball(a ball of dung the female lays an egg in) may get its own room. It’s not uncommon for Tunneler females to stay in their burrow and care for their brood balls until their young hatch.(10) One example of a Tunneler is the Phanaeus vindex .(10)
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Photo of Phanaeus vindex, photo credit to: http://unlcms.unl.edu/entomology/bugbuddies/phanaeus-vindex-male
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Rollers
Rollers or Endocoprids are the group of dung beetles that
have mastered the greatest trait, the ability to create Dung Balls which they
roll(using their back legs) away from the dung pat and bury. These balls are
used for both food and breeding. During the process of rolling the beetle will
periodically climb atop the dung ball and spin around, reorienting itself. It
is thought the trait of ball rolling evolved from the dung beetles desire to
reduce its competition for food. The
further away the roller is from the dung pat, the less likely other beetles
will attempt to eat his or her dung!(Also it resolves an issue of over-crowding
in the area below the dung-pat which can only contain a finite number of tunnelers).
The subfamily Scarabaeinae of Scarabaeidae makes up the rollers and within it
the Scarabaeus sacer is considered
the type-species of the Dung Beetle.(10)(11)
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Two Scarabaeus sacer pushing a dung ball. Source: http://upload.wikimedia.org/
wikipedia/commons/thumb/4/4b/Scarabaeidae_-_Scarabaeus_sacer.JPG/250px- Scarabaeidae_-_Scarabaeus_sacer.JPG |
Dung Beetle Roller forming ball, all credit goes to: Joan Young
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Out of the known species, the mating sequence of Rollers involves the active partner making a brood ball as a sexual display, which the passive partner that the active partner wants to mate with will either accept or decline. The sex of the active partner varies depending on the species. In the tribes Scarabeini and Canthonini it is the male who initiates construction of the ball but in the tribes Gymnopleurinal and Sisyphini it is the female who takes the active role. The construction time of the brood ball varies depending on species but the typical figure of many species is 15-30 minutes, in the case of Scarabaeus sacer it is 32 minutes.(10)
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Once the brood ball is made and a mate is found, the task of rolling the ball to a suitable location begins. Often the brood ball is rolled together by the two partners but in some species the female climbs ontop the ball and makes the male do all the work! During the rolling process other beetles often attempt to steal the ball(most often but not always males of the same species) and so fighting occurs. Once the rolling pair is happy with the location they rolled their ball to, they bury it and create a burrow. In this burrow the male and female copulate and the male leaves. The female stays behind and shapes the ball into a suitable pear shape which she lays an egg in(sometimes two – depending on the species)(10).
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A male attempting to steal another males ball and the female riding on it, all credit goes to: Justin Waldman
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In the case of the Scarabaeus sacer, the female is the one who constructs the brood ball and both male and female push it into position. After the ball has been buried and the female is done sculpting it into a pear shape she leaves a single large egg in it. The fecundity of the Scarabaeus sacer is quite low, a female only producing about half a dozen young in her life.(11)
TED talk called Dance of the dung beetle by Marcus Byrne
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Different species of rollers have shown other remarkable
abilities, for example the African species Scarabaeus
lamarcki uses its dung ball to regulate its body temperature(via its feet)
in the hot sand. It does this through adjusting the frequency and duration of
time it spends ontop of its cool dungball. (12) Another species Scarabaeus nigroaeneus uses the sun and
the stars for navigation during dung rolling.(13) For more information on the
amazing navigation of rollers watch the video Dance of the Dung Beetles to the left.
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Parasitic
The last group of Dung beetles, the Parasitic or
Kleptoparasites don’t do any work themselves. Instead they profit off the work
of other beetles by stealing their dung. The smaller species of dung thieves
target the rollers, one example is the Cleptocaccobius,
it follows the dung being rolled in a zigzag pattern. When it reaches the dung
ball it immediately plunges into it, burrowing inside.(10)
Sources:
(1) http://animals.sandiegozoo.org/animals/dung-beetle
(2) http://www.earthlife.net/insects/dung.html
(3) http://insects.about.com/od/beetles/a/10-Fascinating-Facts-About-Dung-Beetles.htm
(4) http://bugguide.net/node/view/2950
(5) http://www.livescience.com/48944-animal-sex-dung-beetles.html
(6) http://graduatereviews.files.wordpress.com/2013/04/blevins.pdf
(7) http://www.fcps.edu/islandcreekes/ecology/dung_beetle.htm
(8) http://insects.about.com/od/beetles/p/scarab-beetles.htm
(9) http://i.imgur.com/rBbZWTR.jpg
(10) Dung Beetle Ecology, by Ikka Hanski and Yves Cambefort, Princton University Press, Princeton, New Jersey.
(11) http://en.wikipedia.org/wiki/Scarabaeus_sacer
(12) http://news.discovery.com/animals/zoo-animals/dung-beetle-why-poop-cool-feet-protect-121023.htm
(13) http://www.livescience.com/18000-dung-beetles-dance-navigation.html
(1) http://animals.sandiegozoo.org/animals/dung-beetle
(2) http://www.earthlife.net/insects/dung.html
(3) http://insects.about.com/od/beetles/a/10-Fascinating-Facts-About-Dung-Beetles.htm
(4) http://bugguide.net/node/view/2950
(5) http://www.livescience.com/48944-animal-sex-dung-beetles.html
(6) http://graduatereviews.files.wordpress.com/2013/04/blevins.pdf
(7) http://www.fcps.edu/islandcreekes/ecology/dung_beetle.htm
(8) http://insects.about.com/od/beetles/p/scarab-beetles.htm
(9) http://i.imgur.com/rBbZWTR.jpg
(10) Dung Beetle Ecology, by Ikka Hanski and Yves Cambefort, Princton University Press, Princeton, New Jersey.
(11) http://en.wikipedia.org/wiki/Scarabaeus_sacer
(12) http://news.discovery.com/animals/zoo-animals/dung-beetle-why-poop-cool-feet-protect-121023.htm
(13) http://www.livescience.com/18000-dung-beetles-dance-navigation.html