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Just as humans exhibit right- or left-handedness, moths also have a preferred side on which they place their proboscis when inspecting a flower for nectar. This observation was made by Konstanz-based biologists in their latest study. The researchers see this as an example of nature efficiently coping with the limited computational capacity of the insect brain.
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Most people have a preferred hand for tasks such as writing or grabbing a cup of coffee. The same applies to the feet—for example, when playing soccer. Similar preferences are also found across many other animals: Birds, octopuses and insects, among others, often favor either their left or right leg, arm or antenna when performing specific actions.
This so-called lateralization is widespread throughout the animal kingdom and occurs in organisms with a wide variety of nervous systems.
But what about appendages that an animal has only one of—such as our tongue or an elephant's trunk? Even in these cases, lateralization can occur.
In their latest study published in PNAS, research by Lochlan Walsh and Anna Stöckl from the University of Konstanz demonstrated one such example. Their findings reveal that hummingbird hawkmoths—a day-active moth species that, like their namesakes, sip nectar from flowers—have a preferred side to which they extend their tongue-like proboscis while inspecting flowers for nectar.
This may be a solution that nature has developed to enable precise control of actions even in organisms with comparatively simple nervous systems.
A moth's version of handedness
To determine the side to which hummingbird hawkmoths extend their long proboscis, the researchers presented the insects with artificial flower surfaces that the animals approached and inspected.
Using high-speed cameras and computer vision tools, they were then able to reconstruct the proboscis movements in detail and track them relative to the rest of the body.
The researchers found that some individuals tended to place the tip of their proboscis predominantly to the left of their body's midline while inspecting a flower, whereas others showed a preference for the right side. The strength of this side preference varied between individuals, much as the strength of handedness does in humans. Moreover, the individual side preference was already evident from the beginning of the experiment rather than emerging with increasing experience.
"This suggests that proboscis lateralization is an innate trait and that it plays an important role in guiding the moths' flower-inspection behavior," says Stöckl.
Touch where you look
In a further step, the researchers simulated the animals' visual field during flower exploration. They found that hummingbird hawkmoths not only had a preferred side for placing their proboscis, but also a dominant eye for viewing the part of the flower they were touching. The side of this dominant eye consistently matched the side on which the proboscis was preferentially positioned.
"Insects have quite small brains. Aligning the proboscis with the visual field of the dominant eye can save valuable processing capacity when controlling behavior. Rather than constantly recalculating a movement from every possible angle, the animal can rely on a familiar side of its body to guide its actions," Walsh explains.
What came as a surprise was that the alignment of the proboscis with the visual field of the dominant eye was maintained even when part of that eye was experimentally occluded.
"Humans or birds would adapt in such a situation by moving their limb into the visual field of the unobstructed eye. Hummingbird hawkmoths, by contrast, adjust their body position on the flower so that they can view it with the uncovered portion of the dominant eye and preserve their original eye-proboscis strategy," Walsh says.
As a result of the limited computational capacity of their brains, the moths seem to depend on this efficient coordination of the dominant eye and the proboscis.
Taken together, the findings show that precise, flexible behavior does not require a large brain. "Instead, animals can rely on efficient shortcuts built into the relationship between the body, the senses and movement," Stöckl explains. In hummingbird hawkmoths, one such shortcut is the eye and proboscis working as a coordinated unit.
"Each moth solves the challenge of flower inspection through the side preferences of its own body. Our study therefore suggests that lateralization may be one of nature's ways of simplifying difficult tasks—whether that task is reaching for a coffee cup or using the proboscis to search for nectar while hovering in front of a flower."
More information: Lochlan Walsh et al, Conservation of a lateralized visuomotor axis in hawkmoth proboscis probing, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2609365123
Provided by University of Konstanz
This story was originally published on Phys.org.
