The mantis shrimp is a tiny, clown-colored juggernaut of underwater physics. Some species have modified claws that serve as clubs for punching their prey, and the mantis shrimp swings that club fast – its acceleration is comparable to a bullet’s! Moving that quickly in water causes a drastic drop in local pressure, low enough to form a cavitation bubble. Such low-pressure bubbles themselves are not particularly dangerous, but their collapse is incredibly violent, especially near a solid surface, like the shell of the shrimp’s prey. Collapsing cavitation bubbles can send out shock waves, shatter glass, and even generate light. In the case of the mantis shrimp, it’s more than enough to stun, if not outright kill, its prey. (Video credit: Physics Girl)
Tag: biology
Leaping Droplets
Many fungi use coalescing water droplets to launch and spread their spores. The process is recreated in the laboratory in the animation above. Initially, there is a small spherical drop and a second, flattened drop stuck to the backside of the spore. In the animation, the large object on the right is actually both spore and droplet. The spore is spherical on one side and flattened on the other and starts out tipped up on its edge. When the spherical drop gets large enough to reach the flattened drop, they merge. This reduces the total surface area of the drop and thus releases some surface energy. It’s that surface energy that drives the spore’s jump. Even launching just a centimeter away from the host fungus is enough for a breeze to carry the spore further, allowing the fungus to reproduce. (Image and research credit: F. Liu et al., source; submitted by Kam-Yung Soh)
The Hydraulics Behind a Tuna’s Turns
Tuna are remarkably agile for their size. Many species reach lengths exceeding the height of a human adult, yet they can still make tight turns, especially when hunting. A recent study described one mechanism that aids the fish – a built-in hydraulic system for raising its second dorsal and anal fins. The tuna use fluid from their lymphatic system – which produces and transports white blood cells in both humans and tuna – to pressurize chambers at the base of some fins, causing the fin to rise. The extra support puts the fin in a hydrodynamically advantageous position and helps stabilize the fish when turning quickly, allowing them to change direction without slowing. (Video credit: Science; research credit: V. Pavlov et al.)
Hagfish Crash
Last week a flatbed truck in Oregon overturned and released 3400 kilograms of live hagfish on the highway and nearby cars. Hagfish are eel-like fish known for their impressive slime production. When threatened, the hagfish produce mucins that, when combined with water, form an extremely viscoelastic mucus. As it’s stretched, the mucus thickens and becomes more viscous. Normally, hagfish use this property to clog the gills of fish trying to eat them. The slime is weak, however, to shearing; hagfish actually tie themselves in knots to slide the slime off when there’s too much of it. The Oregon Department of Transportation managed to clear the road of mucus (and hagfish) using bulldozers and fire hoses, but it did take them several hours. For more photos and videos from the incident, check out Gizmodo and the Oregon State Police Twitter feed. (Image credit: Oregon State Police; via Gizmodo)
How Hummingbirds Drink
Hummingbirds are incredible acrobatic fliers, capable of hovering for more than 30 seconds at a time, even in windy conditions. Their feeding habits are equally impressive. Many species of hummingbirds have a forked tongue, each half of which curls over like a partial straw. As the bird extends its tongue, its beak compresses the space inside the tongue’s curls. Once in the nectar, both halves of the tongue re-expand, pulling liquid in along the full length of the tongue. For the birds, this is a much faster technique than simply sucking the nectar up like a straw. Hummingbirds can lick nectar more than ten times a second this way. For more gorgeous imagery of hummingbirds, be sure to check out National Geographic’s full feature. (Image credit: A. Varma, source; via Aarthi S.)
The Japanese Pufferfish
[original media no longer available]
If you’ve ever dived or snorkeled over a sandy lake or ocean bottom, you’ve probably seen some neat patterns there. But it’s hard to compete with the Japanese pufferfish for pure artistry. This small fish creates enormous and elaborate designs in the sand in order to attract a mate. The male fish moves the sand into place by flapping his fins very close to the surface. Above a critical flapping velocity, his fins generate vortices capable of picking up sand, as seen below. With repeated passes, the fish is able to excavate the trough that is key to his creation. It’s a constant fight against the current, though.
Puffers aren’t the only ones who flap their fins to move the sands. Rays and flounders use this technique to bury themselves and hide (Video credit: BBC Earth; image credit: A. Sauret, source; research credit: A. Sauret et al.)
Sniffing Underwater
You’d be forgiven for thinking that the star-nosed mole looks funny. Its distinctive star-shaped nose is a highly-sensitive organ, but the mole doesn’t just use it for finding its way through the underground tunnels it lives in. These moles can actually sniff underwater. By exhaling a bubble and then re-inspiring it, the moles collect scent particles that they can use to locate food. In experiments, both star-nosed moles and water shrews could use this technique to successfully follow a scent trail, demonstrating exploring and pausing behaviors similar to terrestrial sniffing as they did. To learn more about this impressive mammal, listen to the latest episode of Science Friday, where research Ken Catania describes his work with them. (Image credits: K. Catania; via Science Friday)
How the Jellyfish Stings
Many jellyfish are capable of venomously stinging both their prey and their predators. The stings originate from specialized cells in their tentacles called nematocysts (middle image) that, when activated, rapidly extend a thin tubule that acts like a hypodermic needle to deliver venom into the jellyfish’s victim (bottom image). The tubules can elongate in about 50 ms – about one-sixth of the time needed to blink your eye. This rapid extension is driven by osmotic pressure – pressure generated when water flows across a semi-permeable membrane in response to chemical changes.
Researchers originally thought all of the osmotic pressure resided in the nematocyst’s capsule end from which the tubule expands, but new work indicates that the tubule is instead pulled along by high osmotic pressure along its moving front. That means that disrupting osmosis at the front – by say, wearing a material with no osmotic potential – can slow down the tubule expansion and stop the jellyfish’s sting. (Image credits: jellyfish – A. Kongprepan; nematocyst – D. Brand; tubule expansion – S. Park et al.; research credit: S. Park et al.; submitted by L. Buss)
The Flying Draco
Nature includes many animals that are so-called fliers: flying squirrels, flying snakes, and draco lizards, to name a few. These animals aren’t true fliers like birds, bats, or insects, though. Instead, they are expert gliders, able to produce enough lift to control their descent and land safely at a distance far greater than a normal leap could carry them. Like the flying squirrel, the draco lizard extends a thin membrane that acts as its wings. The additional area provides enough lift that the lizards can glide as far as 60 m (200 ft) while only losing 10 m (33 ft) in altitude. That’s an impressive glide ratio – about 3 times better than the Northern flying squirrel and twice as good as a wingsuit. (Video credit: BBC/Planet Earth II)
How We Sweat
Sweat plays a critical role in controlling body temperature for humans. Most of the sweat glands on our bodies are eccrine sweat glands, which pump out a mixture of water and electrolytes in response to temperature changes or emotional stimuli. Beneath the surface, these glands consist of three major areas, the tightly bunched secretory coil, where the cells that produce sweat are located; a long dermal duct that transports sweat to the skin surface; and the upper coiled duct just below the pore where sweat exits. Eccrine glands can produce an impressive amount of pressure – about 70 kN/m^2, equivalent to 70% of sea-level atmospheric pressure – to help drive sweat up and out onto the skin. Flow from pores is not steady; like many other biological processes, sweat flow is pulsatile. (Image credit: Timelapse Vision Inc., source; Z. Sonner et al.; submitted by Marc A.)
