Small Wonders: Design in Tiny Creatures
Miniature designs often require more foresight and delicate engineering than large designs. For example, think of how difficult it would be to design a nano air vehicle (NAV) that could flip over and land feet up on a glass ceiling. Yet we hardly notice when a fly does that. Scientists who look more closely at these things often stand in awe of what animals do. Here are some small wonders that deserve our admiration and respect.
Scientists from the U.S. and India slowed down and magnified how flies could land on a ceiling. In their paper “Flies land upside down on a ceiling using rapid visually mediated rotational maneuvers,” published in the AAAS open-access journal Science Advances, they share what they learned.
Flies and other insects routinely land upside down on a ceiling. These inverted landing maneuvers are among the most remarkable aerobatic feats, yet the full range of these behaviors and their underlying sensorimotor processes remain largely unknown. Here, we report that successful inverted landing in flies involves a serial sequence of well-coordinated behavioral modules, consisting of an initial upward acceleration followed by rapid body rotation and leg extension, before terminating with a leg-assisted body swing pivoted around legs firmly attached to the ceiling. Statistical analyses suggest that rotational maneuvers are triggered when flies’ relative retinal expansion velocity reaches a threshold. Also, flies exhibit highly variable pitch and roll rates, which are strongly correlated to and likely mediated by multiple sensory cues. When flying with higher forward or lower upward velocities, flies decrease the pitch rate but increase the degree of leg-assisted swing, thereby leveraging the transfer of body linear momentum. [Emphasis added.]
Penn State researchers, who participated in the study, call this “arguably the most difficult and least-understood aerobatic maneuver conducted by flying insects.” Lead author Bo Cheng said, “Ultimately, we want to replicate that in engineering, but we have to understand it first.” The team was astonished to see how the fly could achieve four “perfectly timed maneuvers” to land upside down in the blink of an eye: acceleration, cartwheel, leg extension, and whole-body swing assisted by the legs.
The fly’s maneuvers “exhibited remarkably high angular velocity,” the scientists found, as they watched how the small insect “cartwheels” around its forelegs. Its body comes well equipped to handle the strain. “This process relies heavily on the adhesion from cushion-like pads on their feet (called pulvilli), which ensures a firm grip, and the viscoelasticity of the compliant leg joints, which damps out impact upon contact.” The research team was apparently too fascinated with the aerodynamics to speculate about evolution.
A fly is also well-equipped for stable flying. Michael Dickinson has been studying insect flight for years in his specialized lab at Caltech. His team published another “remarkable” paper in Current Biology, reporting that “Flies Regulate Wing Motion via Active Control of a Dual-Function Gyroscope.” Fruit flies are members of Diptera (two-wing), because their shriveled-up hind wings, called halteres, have been considered vestigial flight wings. Some have thought they function as gyroscopes. Dickinson decided to test that idea:
Flies execute their remarkable aerial maneuvers using a set of wing steering muscles, which are activated at specific phases of the stroke cycle. The activation phase of these muscles — which determines their biomechanical output — arises via feedback from mechanoreceptors at the base of the wings and structures unique to flies called halteres. Evolved from the hindwings, the tiny halteres oscillate at the same frequency as the wings, although they serve no aerodynamic function and are thought to act as gyroscopes. Like the wings, halteres possess minute control muscles whose activity is modified by descending visual input, raising the possibility that flies control wing motion by adjusting the motor output of their halteres, although this hypothesis has never been directly tested.
Evolutionists who have treated halteres as useless vestigial organs are now going to have to explain even more function than previously thought.
Our results suggest that rather than acting solely as a gyroscope to detect body rotation, halteres also function as an adjustable clock to set the spike timing of wing motor neurons, a specialized capability that evolved from the generic flight circuitry of their four-winged ancestors. In addition to demonstrating how the efferent control loop of a sensory structure regulates wing motion, our results provide insight into the selective scenario that gave rise to the evolution of halteres.
But if the halteres serve useful timing and control functions now, who is to say they were not original equipment? After all, dipterans in general are among the most versatile flyers in the insect world. If something works, as Paul Nelson has pointed out, it’s not happening by accident. “Although the haltere is commonly described as a gyroscope,” Dickinson’s team says, “the structure is better interpreted as a multifunctional sensory organ.” Compared with other insects with four wings, flies have this advantage: “the wing mechanoreceptors can never provide as clean a clock signal as the mechanoreceptors on a haltere.” At best, the benefit can be seen as subfunctionalization of working hindwings. That would represent an example of devolution, not evolution of new functional traits. Like a driver low on gas, he eliminated the trunk to get better gas mileage.
A new land speed record has been discovered in ants. New Scientist writes, “Desert ant runs so fast it covers 100 times its body length per second.” Reporter Michael Marshall doesn’t say if the ant cries “Ouch!” at every footstep on the hot Sahara sand, but this ant looks like a blur as it runs, imitating the Road Runner of cartoon fame. The ant’s trick is to synchronize all six legs and take up to 47 steps per second. Hunting for heat-exhausted insects in the daytime, the Saharan silver ant has another adaptation: its body is coated with silvery hairs that beat the heat.
Nature’s coverage includes a video showing the ant’s running technique slowed down by a factor of 44 — and that is still almost too quick to concentrate on. Galloping at 85 centimeters per second, the ant practically flies with all its feet off the ground at some points in its gait. Touching down with three feet on the ground at a time also gives it stability, like a tripod, that helps keep the ant from sinking into the sand.
NASA’s engineers are trying to solve a problem with their newest lander on Mars, named Insight. Its “mole,” an instrument designed to burrow 16 feet into the Martian soil to measure Marsquakes, is stuck at 14 inches. It was equipped with an inertial hammer for digging, but the soil is proving harder than expected, JPL says. Perhaps they should have mimicked earthworms instead. How do soft, squishy animals manage to loosen the soil so effectively?
Helen Briggs of BBC News reports that “The first global atlas of earthworms has been compiled, based on surveys at 7,000 sites in 56 countries.” The atlas of global earthworm diversity, published by the AAAS in Science, begins by explaining why this is important. “Earthworms are key components of soil ecological communities, performing vital functions in decomposition and nutrient cycling through ecosystems.”
Separately, Liu et al. in Current Biology investigated how “Earthworms Coordinate Soil Biota to Improve Multiple Ecosystem Functions.” Their key concept was “multifunctionality” of soils, which refers to “aggregated measures of the ability of ecosystems to simultaneously provide multiple ecosystem functions.” Their experiments and observations showed that worms offer their vital contribution primarily by “shifting the functional composition toward a soil community favoring the bacterial energy channel and strengthening the biotic associations of soil microbial and microfaunal communities.” Less important were their effects on soil structure and pH. In other words, earthworms cooperate with the soil biota to promote the most possible ecosystem functions.
One cubic meter of soil can contain 150 individual earthworms, the BBC says. How do soft, flexible earthworms squeeze through hard soils, then accomplish so much multifunctional good with small brains and no eyes? These papers don’t get into that, but suffice it to say, without them, Earth soil would likely be as inhospitable as that on Mars.
A Dynamic Planet
At many levels, our privileged planet was designed with the foresight to promote habitability. Environments on a dynamic planet are likely to change. When the habitat changes, organisms must be flexible enough to adapt. Intelligent design theory can support diversification, the “lawn” of life branching at the tips, instead of Darwin’s tree with a single root. The silver Sahara ant, for instance, could have diversified from other ants once the Sahara dried up from its former riparian habitat (as evidenced by river channels detectable under the sand). It would only require modifications or exaggerations of existing traits: body hairs, legs, and behaviors.
There are some 6,000 species of earthworms, including species just a few centimeters in length to giants as long as 3 meters; these also could have diversified based on their local environments. A fly’s hind wings could shrink and degrade if the wings subfunctionalized, moving from multiple purposes to focus on the most important for its needs. This is not too different from blind cave fish that, having lost eyes, compensate with exaggerated senses of touch and smell.
None of these considerations affect the argument from design. Wings, legs, and the ability to burrow do not happen by accident. We can marvel at the foresight built into these creatures that become champions at particular traits in their respective family contests.
Image credit: Penn State (cropped).