Why did such an ordinary little sand pit cause him to fall and die?

Perhaps you often see these small pits in the sand on the roadside. They are shaped like funnels, and even if a flexible ant accidentally falls into them, it is difficult to climb out. What secrets are hidden in these small pits? Why do seemingly ordinary small sand pits become hell for ants?

Funnel-shaped pits in the sand, a mysterious ant hell. Image source: phoenixpestcontroltn.com

At the bottom of the small pits in the sand dunes hides a magical insect called an antlion, which is the larva of the antfly. Antlions are good at digging traps in the sand and mainly feed on ants. When hunting, they are as steady, accurate and ruthless as lions, hence the name antlion.

A magical hunter that only eats and does not excrete

When it comes to ant lions, many people may feel unfamiliar with them, but mentioning their aliases, such as sand monkeys, sand bulls, and ground bulls, will bring back many people's childhood memories. When I was a child in the countryside, there were not many toys, so the children would catch insects everywhere to play with, such as cicadas, longhorn beetles, and scarabs, which are all accompanied by children's beautiful childhood memories.

In addition to the insects mentioned above, antlions are also a favorite of children. As long as you find a "small funnel" in the sand, find a piece of thin grass, and stir it back and forth in the funnel a few times, the antlion will clamp the grass. At this time, just lift it gently and they will reveal their "true face".

A hairy antlion. Image source: rhinorest.com

Antlions are about the size of soybeans, covered with hair, with a big belly and a pair of ferocious-looking sickle-shaped jaws. To be honest, antlions don't look very good, but compared to antlions in their larval stage, their adult ant-flies are much more elegant, with two pairs of transparent membranous wings on their slender bodies. People who are not familiar with them may mistake them for relatives of damselflies or dragonflies.

Ant fly. Image source: mdc.mo.gov

It is common for insects to have large differences in morphology between larvae and adults, a form of development called metamorphosis. Ant flies undergo complete metamorphosis, going through four stages in their life: egg , larva , pupa , and adult .

In nature, it takes at least one year for ants to complete a generation. Generally, the eggs hatch into larvae in the summer, and they guard their traps to hunt, accumulate nutrients, and then emerge as adults in the next summer. However, some species take longer to complete a generation, perhaps two to three years.

The life cycle of an ant lion. Image source: Wikipedia

You may not realize that during the one to three year larval stage, the antfly larvae, also known as antlions, only eat and do not excrete. Because antlions do not have an anus, food residues accumulate at the end of the intestine and are excreted in the form of meconium when they emerge as adults.

No one can stand not excreting for such a long time. In order to make themselves feel better, ant lions have their own unique way to reduce food residues, which is to only suck the juice of the prey instead of gnawing on the prey's body. Specifically, when hunting, ant lions will pierce the prey's body with their mandibles and inject digestive enzymes to digest it into delicious juice, which is then sucked.

Not only that, the ant lion's hunting method of "waiting for food" also makes it less likely to "overeat". They often eat one meal and then another, so they don't eat much, so the accumulated waste is naturally less. In addition, the ant lion has evolved a strong ability to endure hunger. Experimental results show that the ant lion can endure 100 days without food, which is really amazing.

However, compared to the fact that antlions only eat and do not excrete, people may be more curious about how antlions dig traps for hunting?

Ant hell in the dunes

After birth, the ant lion will dig a funnel-shaped trap in the sand and hide at the bottom of the trap, quietly waiting for the prey to fall into the trap. Then, it will use its large jaws to throw sand at lightning speed, knocking the small insects to the bottom of the trap, thus completing a hunt.

An antlion hiding at the bottom of a trap. Image credit: rhinorest.com

Having said so much, let’s first watch a video of an antlion hunting ants to see how the ants fall into the antlion’s trap and are eventually clamped by the antlion’s huge jaws.

Ants fall into an antlion's trap. Video source: References

In the video, an ant accidentally fell into a small funnel-shaped sand pit. At this time, it did not realize what was going to happen next and was still thinking about climbing out of the sand pit. Suddenly, a ball of sand was thrown from the bottom of the sand pit, and the ant was knocked to the bottom of the sand pit. It tried hard to get out of the sand pit, but vaguely there was a big mouth biting the ant...

Are you curious about why ants, which can normally navigate through all kinds of complex terrains with ease, slip in this funnel-shaped trap and keep falling to the bottom of the trap?

The answer actually lies in the antlion's "sand throwing" skill . Scientists have discovered that in the long process of evolution, antlions have evolved a complex trap digging strategy. According to relevant research, when building traps, antlions will classify sand by particle size by throwing sand. This active classification behavior makes the slope surface of the antlion trap covered with finer sand particles. The fine sand is relatively more fluid, which makes the slope of the trap unstable, so that the prey "makes a mistake and regrets it forever."

The distribution of large particles (red) and small particles (blue) in ant lion traps. Image source: References

This unstable structure increases the success rate of hunting, but it is also easily deformed by the struggle of the prey, so the ant lion will regularly maintain the trap by throwing sand. On the one hand, it can prevent the angle of the trap slope from becoming gentle, making it easy for the prey to escape, and on the other hand, it can prevent itself from being buried by the sand sliding down the slope.

It has to be said that the antlion is truly a "master of mechanics" who is proficient in physics, but ants are not completely powerless when facing the antlion.

Ants that escape death by jumping with their jaws

Although the ant lion's trap hunting success rate is very high, it is not always successful. When a type of ant called the trap-jaw ant accidentally falls into a trap, one of their skills can greatly increase the probability of escaping from the "lion's mouth".

Yes, trap-jaw ants rely on their giant jaws.

Over the past 100 years, people have been curious about the amazing jaws of trap-jaw ants, which can close extremely quickly, at a speed of up to 60 meters per second. Unlike the traps dug by ant lions, the huge jaws of trap-jaw ants are natural traps. When their jaws are open, they are like a mousetrap. As long as the prey passes by their mouths, the trap-jaw ants will suddenly close their jaws and bite the prey.

Trap-jaw ants open their jaws and wait for prey to come. Image source: tapatalk.com

When the identity changes from hunter to prey, the trap-jaw ant's large jaws can also help it escape, allowing it to leap out of a dangerous situation by bouncing.

In 2015, a paper published in the journal Public Library of Science studied the success rate of trap-jaw ants jumping to escape by closing their jaws. Scientists glued the mouths of ants with glue, and then let them explore ant lion traps, and compared them with trap-jaw ants whose mouths were not glued, in order to understand the role of jaw jumping.

The mouth of a trap-jaw ant is covered with glue. Image source: References

The experimental results show that trap-jaw ants can indeed help them eject from the sand pit and get rid of the ant lion's entanglement by closing their jaws, but this does not always happen. In 15% of the experiments, the ants escaped by jumping with their jaws. Because not all the time, the jaw closure will successfully allow the ants to jump, the success rate is less than 30%.

For example, in the video below, although the ant finally jumped out of the trap by closing its jaws, there were one or two failures before that successful jump, either it did not jump up or it did not jump high enough.

The ant escapes from the ant lion's trap by closing its jaws. Video source: References

It has to be said that escaping with the mouth is also a technical job. It is worth mentioning that when the lower jaw is glued, the ant's escape probability is almost reduced by half. It seems that it is better to have a big mouth.

In fact, in the fight between ants and antlions, the antlions are not always the winners. In rare cases, antlions can be bitten to death by ants or their mandibles can be bitten off by ants. After all, in the fight for survival, there is often no absolute winner.

References:

[1] Franks, NR, Worley, A., Falkenberg, M., Sendova-Franks, AB, & Christensen, K. (2019). Digging the optimum pit: antlions, spirals and spontaneous stratification. Proceedings of the Royal Society B, 286(1899), 20190365.

[2] Büsse, S., Büscher, TH, Heepe, L., Gorb, SN, & Stutz, HH (2021). Sand-throwing behavior in pit-building antlion larvae: insights from finite-element modeling. Journal of the Royal Society Interface, 18(182), 20210539.

[3] Larabee, FJ, & Suarez, AV (2015). Mandible-powered escape jumps in trap-jaw ants increase survival rates during predator-prey encounters. PLoS One, 10(5), e0124871.

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