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Megasoma actaeon
Range:  widespread in South America
Size:  50 - 120 mm

Of all the rhinoceros beetles of the South American tropics, Megasoma actaeon is surely the one of the largest and most magnificent in appearance.  At 120 mm, it is not quite so long as Dynastes hercules, but its body is broader, often measuring 70 mm across.  There are a number of species of Megasoma, and members of this genus are often referred to as the "elephant beetles" (not to be confused with the large "elephant dung beetles" of the genus Heliocopris which are found in Africa and Asia).  Apart from implying huge size, this name may have also been given due to the form of the beetle's horns.  The robust thoracic horns point forward, looking rather like the tusks of an elephant, and the long cephalic horn is reminiscent of an elephant's trunk.  The armor of the adult male beetle is very smooth to the touch, and it is quite thick and solid.  Some other species of Megasoma are not so smooth in texture, however.  M. elephas of southern Mexico and Central America, for example, has a body that is entirely covered in a fine coat of microscopic yellow-brown hairs.  There are several other Megasoma species which possess this same characteristic.

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As can be seen in this photograph, Megasoma actaeon has a very wide leg span with powerful legs that have large tarsal claws adapted for gripping trees.  M. actaeon is perhaps the most common and widespread of all the South American species of Megasoma.  In the rain forest they are sometimes kept as pets by native children.  Beetles of this size probably have few predators, and are successful simply because they are large.  Some of the animals which are known to prey upon rhinoceros beetles include monkeys and large predatory birds such as owls.  There are also a number of parasitic insects, notably flies, which prey upon the larvae of rhinoceros beetles.

Photo courtesy of Milan Polaczyk.

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Megasoma actaeon (male) - Image  Milan Polaczyk

 
Megasoma actaeon (male) - Image  Milan Polaczyk
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Megasoma actaeon (male) - Image  Milan Polaczyk
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Some side views of an M. actaeon.  Note the small, blunt process which projects from the cephalic horn's base end.  Fighting between male Megasomas was once recorded by American zoologist William Beebe:

"The opponents meet head on and either wait warily for the other to attack or one may rush headlong and begin the encounter.  Usually both wait and spar at a distance.  The object first noticeable is an attempt to use the tarsi of one or both forelegs to trip and unbalance the opponent...  There are quick forward lunges and reachings out with the forelegs...  This may or may not succeed but one will eventually force the fighting and there is straight pushing and butting for a considerable period, exactly like two antlered deer.  Now and then, and effort will be noticed to lower the head and get the cephalic horn beneath the other insect...  Periods of rest or waiting may intersperse the encounter and twice I have seen one beetle to turn and rush after the female.  In both cases the other was after him at full speed and the battle began again..."

Photo courtesy of Milan Polaczyk.

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