Wild Things | Science News

Wild Things

The weird and wonderful in the natural world

Sarah Zielinski

Wild Things


Wild Things

Fire ants build towers with three simple rules

fire ants forming a tower in the lab

Fire ants use a simple set of rules to form a tower, with no leader needed, a new study reveals.

Sponsor Message

View video

When faced with rushing floodwaters, fire ants are known to build two types of structures. A quickly formed raft lets the insects float to safety. And once they find a branch or tree to hold on to, the ants might form a tower up to 30 ants high, with eggs, brood and queen tucked safely inside. Neither structure requires a set of plans or a foreman ant leading the construction, though. Instead, both structures form by three simple rules:

  1. If you have an ant or ants on top of you, don’t move.
  2. If you’re standing on top of ants, keep moving a short distance in any direction.
  3. If you find a space next to ants that aren’t moving, occupy that space and link up.

“When in water, these rules dictate [fire ants] to build rafts, and the same rules dictate them to build towers when they are around a stem [or] branch,” notes Sulisay Phonekeo of the Georgia Institute of Technology in Atlanta. She led the new study, published July 12 in Royal Society Open Science.

To study the fire ants’ construction capabilities, Phonekeo and her Georgia Tech colleagues collected ants from roadsides near Atlanta. While covered in protective gear, the researchers dug up ant mounds and placed them in buckets lined with talc powder so the insects couldn’t climb out. Being quick was a necessity because “once you start digging, they’ll … go on attack mode,” Phonekeo says. The researchers then slowly flooded the bucket until the ants floated out of the dirt and formed a raft that could be easily scooped out.

In the lab, the researchers placed ants in a dish with a central support, then filmed the insects as they formed a tower. The support had to be covered with Teflon, which the ants could grab onto but not climb without help. Over about 25 minutes, the ants would form a tower stretching up to 30 mm high. (The ants themselves are only 2 to 6 mm long.)

Article continues below video

To make a tall tower or a floating raft, fire ants follow the same set of rules. Candler Hobbs and David Hu

The towers looked like the Eiffel Tower or the end of a trombone, with a wide base and narrow top. And the towers weren’t static, like rafts of ants are. Instead, videos of the ant towers showed that the towers were constantly sinking and being rebuilt.

Peering into the transparent Petri dish from below revealed that the ants build tunnels in the base of a tower, which they use to exit the base before climbing back up the outside.

“The ants clear a path through the ants underneath much like clearing soil,” Phonekeo says. Ants may be using the tunnels to remove debris from inside the towers. And the constant sinking and rebuilding may give the ants a chance to rest without the weight of any compatriots on their backs, she says.

To find out what was happening inside the tower, the researchers fed half their ants a liquid laced with radioactive iodide and then filmed the insects using a camera that captured X-rays. In the film, radioactive ants appeared as dark dots, and the researchers could see that some of those dots didn’t move, but others did.

The team then turned to the three rules that fire ants follow when building a raft and realized that they also applied to towers. But there was also a fourth rule: A tower’s stability depends on the ants that have attached themselves to the rod. The top row of ants on the rod aren’t stable unless they form a complete ring. So to get a taller tower, there needs to be a full ring of ants gripping to the rod and each other.

That such simple rules could form two completely different structures is inspiring to Phonekeo. “It makes me wonder about the possibilities of living structures that these ants can build if we can design the right environment for them.”

Animals,, Evolution,, Conservation

Kauai’s native forest birds are headed toward extinction

By Sarah Zielinski 3:00pm, September 13, 2016
Kauai’s honeycreepers are losing their last refuges from mosquito-borne diseases that are spreading due to climate change. Some could become extinct within a decade.
Animals,, Conservation

As IUCN votes on ivory trade, elephants’ future looks bleak

By Sarah Zielinski 9:34am, September 9, 2016
As the IUCN prepares to debate an end to the ivory trade, two new reports show just how poorly Africa’s elephant species are faring.
Animals,, Evolution

Tail vibrations may have preceded evolution of rattlesnake rattle

By Sarah Zielinski 7:00am, August 31, 2016
The rattle on a rattlesnake evolved just once. A new study contends it may have come out of a common behavior — tail vibration — that snakes use to deter predators.
Animals,, Evolution

The weird mating habits of daddy longlegs

By Sarah Zielinski 11:00am, August 22, 2016
Scientists studying the sex lives of daddy longlegs are finding there’s a lot of diversity among this group of arachnids.
Animals

Lizard mom’s microbiome may protect her eggs

By Sarah Zielinski 5:19pm, August 16, 2016
Striped plateau lizard moms don’t do any parenting beyond laying eggs. But they may convey protection from pathogens with help from their microbiome.
Animals,, Ecology

Capybaras may be poised to be Florida’s next invasive rodent

By Sarah Zielinski 11:30am, August 12, 2016
Some capybaras have escaped their owners in Florida. Others have been set loose. Now there are fears the giant rodents could become established in the state.
Animals

Bird-friendly yards have a major downside — for birds

By Sarah Zielinski 7:00am, August 3, 2016
Vegetation and feeders bring birds into our yards. But those lures also bring more birds to collide with the windows in our homes.
Animals,, Oceans

Pup kidnapping has a happy ending when a seal gets two moms

By Sarah Zielinski 12:48pm, July 29, 2016
A female fur seal kidnapped another seal’s pup. But this turned out to be a positive the young seal, scientists found.
Oceans,, Ecology

Sea ice algae drive the Arctic food web

By Sarah Zielinski 1:00pm, July 26, 2016
Even organisms that don’t depend on sea ice depend on sea ice algae, a new study finds. But Arctic sea ice is disappearing.
Animals

Tiny ants move a ton of soil

By Sarah Zielinski 9:00am, July 20, 2016
For the first time, scientists have quantified how much soil ants move underground.
Subscribe to RSS - Wild Things