Reading Ed Yong’s book “An Immense World”: Wasps, Star Mole Rats, and Red Knots

I continue to read Ed Yong’s book “An Immense World”. There is the interesting story about the emerald jewel wasp (Ampulex compressa). This wasp, a beautiful creature an inch long with a metallic green body and orange thighs, is a parasite that raises its young on cockroaches. When the female Ampulex compressa finds a cockroach (twice her size), she stings it twice: first in the middle of the body to temporarily paralyze its legs, and a second time in the brain. The second sting targets two specific groups of neurons and delivers a venom that deprives the cockroach of the desire to move voluntarily, turning it into an obedient zombie. In this state, the wasp can lead the cockroach to its lair by the antennae, as a person leads a dog. There, she lays an egg on it, providing her future larva with a compliant source of fresh meat.

This act of mind control depends on the second “sting,” which the wasp must deliver precisely to the right place in the brain. There is almost no brain there :-) in the cockroaches, and what is there is hidden somewhere among the tangle of muscles and internal organs. How does she manage? Fortunately for the wasp, her stinger is not just a drill, venom injector, and egg-laying tube, but also a sensory organ. Its tip is covered with tiny bumps and indentations, sensitive to both smell and touch. With their help, she can detect the cockroach’s brain. When Gal and Libersat removed the brain of a cockroach before offering it to the wasp, she tried to find the organ, but in vain. If the brain was replaced with something of the same consistency, the wasp found the brain but then became confused. So, she distinguishes the brain from everything else with her nose.

Another interesting story is about shorebirds, the red knots. There are many such birds in the ocean, poking their beaks into the sand along the shore in search of buried treasures — worms, molluscs, and crustaceans. Under the microscope, the tips of their beaks are pitted like corncobs with all the grains eaten off. These pits are filled with mechanoreceptors, similar to those on our skin, especially on the palms and fingers, and allow the birds to detect buried prey by touch.

But how does a shorebird know where to insert its beak first? Underground prey is not visible from the surface, so one might assume that the birds just randomly dig and hope for the best. However, in 1995, Dutch scientist Theunis Piersma showed that the birds find molluscs eight times more often than one would expect if they were searching randomly. They must have some technique. To figure it out, Piersma trained birds to inspect buckets filled with sand for buried objects and indicate if they found something by approaching a specially equipped feeder. This simple experiment showed that the birds can detect molluscs buried even deeper than they can reach with their beaks. In the process, it turned out that they were able to feel stones, so they clearly did not rely on smells, sounds, tastes, vibrations, heat, or electric fields.

Piersma suggested that these birds use a special form of touch that works at a distance. When a red knot’s beak is immersed in wet sand, it “pushes” thin jets of water between the grains, creating a wave of pressure that spreads in different directions from that point. If any solid object (say, a mollusc or stone) is encountered along the way, the water has to flow around it, distorting the pressure pattern. The pits on the tip of the red knot’s beak are tuned to sense these distortions. Moreover, the bird “collects” data from its radar at different points, allowing it to make fewer attempts than if it were acting by a method of unscientific poking. This is a hypothesis, but it is supported by experiments that make it very likely. Because nothing else explains the observed behavior.

Ed also writes interestingly about star-nosed moles. This is a creature without eyes, with a large red star on its nose. This star-shaped growth is the most sensitive tactile system known to modern science. Biologists have counted more than 100,000 nerve fibers in it: five times more than in the human hand, which is also considered to have very high sensitivity. And these 100,000 are packed into an organ smaller than the tip of a finger. Sensory receptors known as “Eimer’s organs,” named after the scientist who first observed them, help the mole detect seismic vibrations from the environment.

Thanks to the huge number of sensory receptors, the star-nosed mole can find an object, determine whether it’s edible or not, and then eat it (if it’s an insect or worm) in less than 120–150 milliseconds. That’s the time it takes for us to blink. In that time, having touched, say, a worm, they understand that it’s edible and manage to “chew” it even before we finish blinking. As a result, the star-nosed mole can touch and check up to 13 different small objects per second. Data exchange happens fantastically fast: the brain makes a decision in 8 milliseconds, which is the theoretical speed limit of neurons.

Their sense of smell is also unusual. It’s generally believed that mammals cannot smell underwater. But this creature can. To do this, moles use a unique technology. Chasing prey in swampy areas, they blow bubbles into the water, then inhale them back through their nostrils. The direction of their movement correlates with the movement of the prey.