Key points
- Darkling beetles are one of the largest families of beetles.
- We've sequenced the DNA of darkling beetle specimens to reconstruct their evolutionary tree.
- Evolutionary changes in these beetles' body forms are associated with shifts in their environment.
Darkling beetles (Tenebrionidae) are a family of beetles. There are over 30,000 species worldwide.
Yun 'Living' Li, a postdoctoral researcher at our Australian National Insect Collection, studied them during his PhD.
To find out more about the characteristics of darkling beetles, we asked Living to put them through a decathlon. Here's how they measured up in the beetle Olympics.
(No beetles were harmed in this thought experiment.)
100 meters
Gold medal: Yellow Mealworm Beetle (Tenebrio molitor) is a speedy beetle
Mealworms, used as pet and human food, are the larval (childhood) stage of this species. The adults are black and active at night, like you might expect a 'darkling' to be. But darkling beetles have a huge variety of shapes and lifestyles.
"You can find darkling beetles in your backyard, wet rainforests, deserts, mountaintops, alpine heaths and more," Living said.
Long jump
Encouragement award: Egyptian Darkling Beetle (Blaps polychresta) looks like it might jump
The Egyptian Darkling Beetle from Africa can raise its hind legs into a sort of headstand that looks like it might be about to jump. In fact, it is threatening to spray a smelly liquid.
Recently, this species has become a notorious pest across semi-arid areas of Southern Australia. We have some specimens in our insect collection.
"We sequenced the DNA of over 300 darkling beetle specimens in our collection to reconstruct the evolutionary tree of darkling beetles. It led to some unexpected discoveries," Living said.
Shot put
Disqualified: Cylindrical Darkling Beetle (Corticeus unicolor) for not even trying
No creature can come close to a dung beetle’s ability to roll a shot (made of poo) a long way. But dung beetles are in a different beetle family: Scarabaeidae.
We disqualified the Cylindrical Darkling Beetle for not even giving shot put a go. This species lives in tunnels made by beetles called ambrosia beetles, which burrow into trees to farm fungi for their larvae.
"This species has a cylindrical shape but is very closely related to the species that won the discus event, which has a hemispherical shape," Living said.
"We found darkling beetles that are closely related can look very different.
"To find out why, we compared darkling beetle body shapes with their ecology. We found evolutionary changes in body forms were driven by shifts in the environments where darkling beetles live."
High jump
Bronze medal: Shiny Darkling Beetle (Amarygmus morio) ‘jumps’ a long way when startled
Darkling beetles lost this event to beetles in the family Mordellidae. The latter are also known as tumbling flower beetles and are excellent somersault jumpers.
Shiny Darkling Beetles shelter under bark or in woody fissures during the day. At night they feed on lichen and fungi on the surface of tree trunks. If you touch one of these beetles, it will drop off the tree onto the ground and play dead.
"Although no living species of darkling beetle can jump, rapid jumps (quantum evolution) explain how darkling beetles shape shift," Living said.
"Rapid jumps occurred frequently across the darkling beetle evolutionary tree, which allowed these beetles to shift their body forms to rapidly adapt to changing environments.
"This is the secret to their ecological success," Living said.
400 meters
Gold medal: Fog-basking Darkling Beetle (Onymacris unguicularis) speeds through inhospitable environments
This species has unique skills to cope with hot and dry environments of the Namib desert, a coastal desert in southern Africa.
When fog rolls over sand dunes in the early morning, they do 'headstands'. Microstructures on their body condense water from the fog and direct it into their mouth.
In the middle of the day, they race over the sand in search of food. Their very long legs enable them to hold their bodies clear of hot sand.
"Looking back in time, we found that darkling beetles evolved from a common ancestor that thrived in humid forests around 150 million years ago," Living said.
"Arid adaptations arose at least 17 times, allowing them to survive in some of the harshest environments on Earth."
110-meter hurdles
Gold medal: Giant Darkling Beetle (Cyhaleus imperialis) runs over complex terrain
This is a large species of darkling beetle, around five centimetres long. It lives in Australia's wet tropics.
They scurry along the ground among leaf litter and climb over dead logs, just like doing the hurdles. They have a powerful chemical defence system that they can spray from their bums.
"Darkling beetles have gained and lost traits like chemical defence systems many times throughout their evolution. This used to make it difficult to use their traits to tell which species were closely related," Living said.
"We solved this by uniting museum collections with DNA sequencing to construct their evolutionary tree."
Discus throw
Gold medal: Hemispherical Darkling Beetle (Derispia variabilis) is round, like a discus!
These beetles are unique, both in terms of their body shape and the environments they live in. They forage on rocks or wood for algae, lichen, and moss. They are round, like ladybirds (which are not darkling beetles), which protects their legs and antennae against predators.
"Interestingly we found that darkling beetles underwent a big bang of evolution near the end-Cretaceous mass extinction, the time when dinosaurs went extinct," Living said.
"This is a significant event in darkling beetle history. They colonised a vast range of terrestrial environments across the planet, eventually evolving into a spectacular array of body forms that we see today."
Pole vault
Gold medal: Green Comb-clawed Beetle (Lepturidea viridis) climbs 'poles'
It's not quite a pole vaulter, but this species has a slim body shape to climb plants and perch on leaves or flowers.
These beetles are pollinators and have the nickname 'darkling skywalkers'.
"Our research showed that darkling beetle species that specialise in 'foliage walking' have evolved slim 'skywalker' body forms many times in species that aren't closely related," Living said.
"This process is called convergent evolution."
Javelin throw
Silver medal: Beach Bum Beetle (Caediomorpha heteromera) is a sand swimmer
This event was won by Onychocerus albitarsis, a species from Peru that uses its long antennae to sting! It's in the Longhorn beetle family, Cerambycidae.
The silver medal went to the Beach Bum Beetle, which impressed us with its athletic agility. This beetle has a spherical body shape and shovel-like 'front arm' and swims through sand by the sea.
"Darkling beetles have evolved to colonise a diverse range of microhabitats. We found over 60 microhabitat shifts over the course of their evolution," Living said.
1500 metres
Gold medal: Pie-dish Beetle (Helea monilifera) is an endurance runner
This species lives in the arid deserts of Australia. They forage at night and can travel a long way in search of food. Their bodies are a strange shape, like a pie dish.
Living once watched one of these beetles using its unique shape to defend itself against ants. It tipped over, using its pie dish like a Roman shield.
"This species is part of a group that includes more than 500 species on the Australian continent. Species in this group evolved different body forms quickly at a time when Australia’s environment was shifting into a largely arid continent," Living said.
"Ecological adaptation has driven darkling beetle diversity."