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A Flea Circus of Small Animal Acrobats

Photo: Common darter, by Loz (L. B. Tettenborn), CC BY-SA 3.0 , via Wikimedia Commons.

A “flea circus” is mostly known today as a metaphor for some minor novelty, but there actually used to be flea circuses. These sideshows, the BBC says, were popular between the 1830s and 1960s. Flea circus ringmasters took advantage of the tiny insects’ powerful legs to get them to pull chariots, fire cannons, or turn carousels in miniature arenas, to the amusement of bystanders. The article shows fleas magnified and some historic shots of flea circus acts.

Today’s flea circus will feature a cast of additional small actors that can amuse and inspire, especially when consideration is given to the engineering design that makes their performances so extraordinary.

Snappy-Fast Crustacean

There’s a beach dweller with a claw almost as big as its body. Males of a species of amphipod, a type of crustacean, can snap the claw faster than almost any other beast can move any body part. And they can do it repeatedly without breakage! One super-performer found in coastal waters off North Carolina was featured in Current Biology:

Males use their enlarged major claw, which can exceed 30% of body mass, to snap a 1 mm-long dactyl with a diameter equivalent to a human hair (184 μm). The claw snaps closed extremely rapidly, averaging 93 μs, 17 m s-1, and 2.4 x 105 m s-2. These snaps are among the smallest and fastest of any documented repeatable movement, and are sufficiently fast to operate in the inertial hydrodynamic regime (Reynolds number (Re) >10,000). They generate audible pops and rapid water jets, which occasionally yield cavitation, and may be used for defense. These amphipod snaps push the boundaries of acceleration and size for repeatable movements, particularly in water, and exemplify how new biomechanical insights can arise from unassuming animals. [Emphasis added.]

You can watch the action in a video in the open-access paper. S. Patek of Duke University narrates, showing the critter in detail. She tells how the team captured slow-motion video of the ultrafast snaps at 300,000 frames per second. The movements are “spectacular,” she says: “tiny and fast” — so fast, in fact, that they sit at the boundary of what is physically possible. The authors apparently had no need of Darwinian theory to explain what they found.

Dragonfly Gymnast

Athletic humans can do backflips; dragonflies do them, too. You can watch them both do backflips in a video from Imperial College London, where researchers used high-speed cameras to watch how dragonflies right themselves when thrown off balance. Unlike cats and hoverflies, which do a twisting/rolling motion to turn upright when falling, dragonflies somersault backwards to regain their orientation. The backflip maneuver must be built into the insect’s wing design, because even unconscious dragonflies were seen to do it. That gives the researchers ideas that mimicking the dragonfly trick could help engineers design drones able to automatically right themselves. Pause briefly for the Darwin commercial:

“Passive stability lowers the effort requirements of flight, and this trait likely influenced how dragonfly shapes evolved. Dragonflies that use passive stability in flight are likely to have an advantage, as they use less energy and are better able to recover from inconvenient events.”

Spider Weightlifter

Spiders can hoist prey that are much heavier than they are. How do they do it? Researchers in Italy at the University of Trento, according to, found that the spiders use pre-tensioned silk. The scientists let spiders build their webs in boxes, then watched what they would do when fed with South American cockroaches that were much larger than they are.

The researchers found that the spiders would repeatedly spin a length of silk, stretch it slightly, then affix one end of it to the body of the cockroach and the other to an upper part of the web. The spider used its own body weight to stretch the silk like a rubber band. As the spider attached more strands to the cockroach, it was eventually lifted entirely off of the floor, making it impossible to escape.

The stretching action had to have “just the right tension — too much, and they would lose their elasticity, too little would mean wasted effort.”

Incidentally, Fritz Vollrath and colleagues at the University of Oxford have determined that web spinners are able to “outsource” some of the work from the brain to the legs. The legs can work semi-autonomously on many of the repetitive tasks of web building. This is a natural application of decentralized intelligence, he says at The Conversation

Our study has shown that spider legs have “minds of their own”, constructing webs without the oversight of the spider’s brain. This has important implications for the field of robotics, which may take inspiration from this example of decentralised intelligence to build similarly autonomous robot limbs.

Tardigrade Sunscreen

Water bears (tardigrades) are already well-known champions in the survival class. A researcher from the Indian Institute of Science in Bangalore, inspired by a Cosmos episode on tardigrades, decided to investigate them further. The Scientist tells how Sandeep Eswarappa and his colleague Harikumar Suwa wanted to learn about the tardigrades’ amazing resistance to damage from UV light. When their subjects came out of a UV bath that would have killed most microorganisms, the team first noticed that the coating, whatever it was, fluoresced under UV light. They ground it up into a paste and put it on roundworms. The roundworms gained UV resistance as if they had been given a sunscreen.

Independent research, the pair found, showed that the coating was due to a protein named Dsup (damage suppressor). This protein also confers resistance to X-ray damage. Additional research showed that Dsup creates a protective cloud around chromatin, protecting it from mutations. Ideas that could help us humans came from this work:

Studies such as Kadonaga’s and Eswarappa’s could have practical applications, the researchers say. Dsup or other related proteins, for example, could be used to extend the life of cell lines created to manufacture proteins, or of T cells engineered to combat cancer. “You might be able to make cells that are tougher, more robust, that might last longer,” Kadonaga says. Tardigrades’ newly discovered fluorescent molecules, meanwhile, could be used in sunscreen or UV-repellant glasses, Eswarappa says.

More Will Come

This flea circus is never over. New acts are added all the time as researchers look closer at “unassuming animals” that remind us, “never assume.”