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A Monarch-Like Wonder from Mountains Down Under


There’s a little gray moth in Australia that does something extraordinary. Like the Monarch butterfly of North America, it migrates over long distances. Unlike the Monarch, it flies at night. And it doesn’t even need to.

Current Biology describes this dull-colored little wonder, called the Bogong moth, as the “nocturnal counterpart of the migratory Monarch butterfly.” Its summer home is as amazing as the mountain forests of Mexico where the Monarchs were discovered.

If you ever have the chance of hiking the Australian Alps in summer, you will find an ancient and beautiful mountain range. The grassy, treeless peaks, polished aeons ago by glaciers, are littered with countless granite boulders of all shapes and sizes. If you are not claustrophobic and dare to climb into one of the crevices formed by these rocky ensembles, your breath will be taken away, first by the dense clouds of ultra-fine, silvery dust drawn to your face by swift air currents channelled through the rock chimneys, and then by the sight of the source of the dust: hundreds of thousands of Bogong moths, neatly tiling the cave walls. In fact, there are about 17,000 of them per square meter, but you will only find them by chance if you are very lucky. This is because we only know of a handful of such caves, and the moths are present there only for four months during the height of the Australian summer. [Emphasis added.]

These moths were a source of food for aboriginal people, who found them in the mountain plains each summer. It took scientists more recent study to discover the rest of their “remarkable and interesting” tale: that they migrate a thousand kilometers from southern Queensland to these mountain caves each year. Here’s how they outperform the Monarchs as navigators:

All this makes the Bogong moth, in many respects, similar to the iconic North American Monarch butterfly Danaus plexippus, except that it is a night-active species and therefore cannot use the sun for orientation. And unlike the Monarch butterfly, where the full forward and reverse migrations are performed by several generations, individual Bogong moths perform both migrations. If you think of the Monarch butterfly as the King of insect migration, the Bogong moth is certainly insect migration’s Dark Lord.

Scientists don’t know how they find their way without sunlight. Monarchs are known to use the polarization of light as it changes throughout the day; in fact, our neighbors at the University of Washington believe they have figured out the secret of the Monarchs’ internal compass at long last. But Bogongs only have the moon, the stars and the earth’s magnetic field to provide visual cues. While these might guide them in the basic direction, what leads them specifically to the caves?

The Bogong moth’s journey can thus be divided into a long-distance part and a final travel segment that lets them locate their specific target site. As the two parts operate on very different spatial scales, the mechanisms employed, and the information used, are likely not identical. To find their caves, Bogong moths might, for example, use their sense of smell and be attracted to the carcasses of those family members that were not fit enough for last year’s return trip.

Let’s see if authors Stanley Heinze and Eric Warrant can provide a Darwinian explanation. “Given the lengthy, difficult, and often lethal journey, there must be substantial selection pressure driving these animals along their migratory cycle,” evolutionary theory would expect. “Nevertheless, and again similar to the Monarch butterfly, not all populations of Bogong moths are migratory.” In fact, they say, there are non-migrating populations of Bogongs at both ends of the route and in other places. This defies evolutionary expectations so clearly, the authors never return to the question of what selection pressures might possibly create this remarkable behavior. They only mention additional examples of insects with mixed populations of migrants and non-migrants, confessing that “the migratory movements of these species are either erratic or poorly understood.”

The performance of the little night-flying Bogong moth is enough, by contrast, to generate rhapsodic praise:

Bogong moths pinpoint a tiny mountain cave from over a thousand kilometres away, crossing terrain they have never crossed previously, and locating a place they have never been to before. Moreover, they do all this at night, fuelled by a few drops of nectar and using a brain the size of a grain of rice. Don’t even ask an engineer if they could build a robot equivalent! To achieve this remarkable behaviour, the moth brain has to integrate sensory information from multiple sources and compute its current heading relative to an internal compass. It then has to compare that heading to its desired migratory direction and translate any mismatch into compensatory steering commands, while maintaining stable flight in very dim light while buffeted by cold turbulent winds.

On top of all that, the moth has to switch all its computations to the opposite direction come autumn, and reverse all its learned behaviors. “Its simple nervous system and its fixed, reproducible behaviour stand in stark contrast to the complexity of the problem that the Bogong moth must solve.”

Here’s where intelligent design can make a contribution. Because science can employ “electrophysiology, neuroanatomy, and behavioural analysis” to study this stable population, we can bestow upon these insects a better reputation than accidental products of bind selection pressures. We can, instead, reverse engineer the software that takes neural circuits that underlie “nocturnal vision, sensory integration, motor control, action selection and state-dependent changes of behaviour.” As a result of design thinking, we might even be able to apply the knowledge gained to our own designed systems.

Seeing in the Dark

A related paper in Current Biology examines the question of how moths see to fly at night. Here’s the upshot:

A new study shows that moth vision trades speed and resolution for contrast sensitivity at night. These remarkable neural adaptations take place in the higher-order neurons of the hawkmoth motion vision pathway and allow the insects to see during night flights.

Author Petri Ala-Laurila waxes eloquent about the difficulty of operating in the dark.

Seeing under very dim light poses a formidable challenge for the visual system. In these conditions, visual signals originating in a small number of photoreceptor cells have to be detected against neural noise originating in a much larger number of such cells, as well as in the neural circuitry processing these sparse signals. The randomness of rare photon arrivals makes it even harder to form reliable visual percepts in dim light. Yet many species show remarkable visual capabilities at extremely low light levels.

We are on that list; “dark-adapted humans can detect just a few light quanta absorbed on a small region of the peripheral retina.” Nevertheless, hawkmoths are experts at deriving the most from the least, along with cockroaches, dung beetles, toads and Central American sweat bees. “In all of these cases, the striking behavioral performance of animals in dim light exceeds that of individual receptor cells at their visual inputs by orders of magnitude.

The secret, the author explains, is in the processing. Take what you have, pool it, and boost it. Summing the inputs adds clarity over time. “In our own retina, rod photoreceptors used mainly at low light levels have a longer integration time than cone photoreceptors that we use in daytime,” Ala-Laurila says. “This is one example of receptor-level temporal summation.”

There are tradeoffs, however; “Unfortunately, there is no free lunch — especially not in biology.” Pooling and boosting adds noise, lowers resolution, and takes longer to compute. Imagine a moth flying in the dark, darting rapidly to avoid predators. You would think it needs a high-speed visual computer to do what it does. “Balancing sensitivity against acuity and speed is a trade-off problem where the optimal solution depends on light level and motion velocity.” Remember back when we talked about optimization as an example of intelligent design science in action?

Ala-Laurila points to a study that quantified the amount of summation going on in the hawkmoth’s brain and eyes. How the scientists did that is quite a trick, but they found out that the summation circuitry gives the moth a hundredfold boost in sensitivity, using nonlinear processing. A dim image, therefore, becomes quite bright as the scientists show in a comparison between original and processed images.

Another study we discussed last year showed that the moth’s behavior is perfectly tuned to the motions of the flowers they seek at night for nectar. “These two studies together suggest that the neural mechanisms of the moth visual system have been matched perfectly to the requirements of its environment.” What luck for Darwinian selection to get mutations in both systems to match up perfectly! Evolution is beautiful.

Similarly, it will be intriguing to understand the mechanisms that control the optimal tuning of spatial and temporal properties across multiple light levels in the moth. Recent studies have unraveled neural circuit mechanisms underlying luminance-dependent changes in the spatial summation of the vertebrate retina. Further mechanistic understanding of evolution as an innovator at visual threshold might even help us to build more sensitive and efficient night vision devices in the future. Aside from these potential future innovations, this study reveals above all some of the key neural secrets underlying the night flight of a moth in the wilderness. This understanding as such is simply beautiful.

Evolutionists at the University of Basel are even claiming that Darwinian evolution is helping moths adapt to city life by making them avoid bright lights. One can always invent a story about how blind processes achieve perfection, but returning to reality, we know design when we see it. Whether the Monarchs shown in Illustra Media’s documentary Metamorphosis: The Beauty and Design of Butterflies or the night navigators described here (Bogong moth and hawkmoth), we just need to recognize what it points to.

There is “no free lunch — especially not in biology.” Aimless natural processes are woefully inadequate to deliver precision guided systems. Intelligence, by contrast, provides a feast for understanding.

Image: Bogong moth, by CSIRO [CC BY 3.0], via Wikimedia Commons.

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