The Hercules Beetle

Pol Turon Contreras 

Imagine an animal, biggest of its kind, with large horns almost as long as his body that can lift up 10 times its own body weight, with colour changing abilities and its young can bite straight through wood, well that's the amazing species we’ll be talking about today, the hercules beetle.

The hercules beetle, (Dynastes hercules), is a species of rhinoceros beetles native to central and south america, mostly in montane or tropical rainforests. The hercules beetle is the longest insect still alive today, with the males of this species reaching up to 173mm in length and weighing 140g, although the females only get up to 85mm long. They are capable of flying but due to their large size they’re not very efficient so they rarely do it. These beetles are surprisingly strong with some studies saying they can lift up to 100 times their body weight, although they could only sustain a steady speed while holding 30 times their weight. This impressive strength is why they are named after the Greek mythological figure Hercules, a demigod known for his strength.

Image credit: Greg Carter

Hercules beetles are sexually dimorphic, meaning that there are very noticeable differences between the two sexes of the species. Male hercules beetles have two large horns on their heads, one on top of the other with the lower one being slightly shorter, while females don’t although they have a larger body than the males. This big difference between the two sexes is due to the males having to fight other males to get the right to mate with the females. This usually occurs when heavy rainfall comes, around the months between July and December.

This all starts with the female hercules beetles releasing pheromones that attract males in the area. When multiple males arrive they start competing for a chance to mate by trying to grab the other males with their massive horns and then throw them back down or even flip them to disorient their opponent or knock them over branches. This continues until all males but one give up and retreat and the remaining male gets to mate with the female. After mating the female will look for a piece of rotting wood and lay around 100 eggs there.

When the eggs emerge they are worm like larvae that look very different compared to the adults. These larvae are very important to the forest ecosystems they live in because they are saproxylic, meaning they eat dead wood.

This is important because wood, while incredibly rich in nutrients, is incredibly hard to break down due to the high amounts of lignin it has. While most plants mostly have molecules like cellulose and hemicellulose to make up their structures, wood has another molecule called lignin, which makes a protective layer around the cellulose and hemicellulose that makes them very hard to digest. Since it's so hard to digest, there aren’t many species that can consume the wood and break free all the nutrients it has. This makes the larvae of hercules beetles essential for the ecosystem since they can break down the rotting wood and return nutrients back into the soil making it more fertile.

The larvae do this by having many different types of bacteria inside their digestive track that can break down the lignin and cellulose inside the wood.

Larvae spend all their time eating wood to grow as big as they can, they molt three times throughout their larval stage and then after 19 to 21 months the larvae turns into a pupa and after 20 days it emerges as an adult hercules beetle, which usually live for about three to six months more. 

While the male hercules beetles have very big horns paired with substantial strength, they’re actually not that good at hunting due to a lack of speed and the horns being quite dull, so these insects are gentle giants that in their adult stage only eat rotting fruit such as bananas or mangoes, or they carve small holes on trees and use a narrow opening to suck in the sap. The horns are also not very effective at defending themselves against predators so adults usually stay in the undergrowth of the forests and hide during the day only coming out during the cover of the night to feed. When disturbed they can release a foul smelling odor to deter predators and look unappetising and make a hissing sound by rubbing their abdomens and elytra together to warn predators.

Adult hermes beetles have an interesting adaptation in their elytra that makes them able to change colour from yellow to black depending on the humidity of their environment. They can do this because their elytra is made up of three parts, a waxy and transparent top layer, a porous yellow or olive green middle layer and a black, thick and leathery bottom layer. When the humidity is below 80%, the porous middle is filled with air so light can reflect from that layer and it appears yellow or olive green. When the humidity is above 80% the pores in the middle layer fill with water, and when light changes its medium from air to water it causes it to bend and get absorbed by the black layer at the bottom.