Phototaxis:
noun BIOLOGY
- the bodily movement of a motile organism in response to light, either towards the source of light (positive phototaxis) or away from it (negative phototaxis).
(Definition from Oxford Languages)
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Phototactic responses are primarily found in organisms such as zooplankton, green algae, jellyfish and insects for purposes both evolutionary and arbitrary. For some organisms, the advantages of phototaxis includes having the ability to regulate light exposure, find food, facilitate larval dispersal or increase the likelihood of gamete fusion (Jékely, 2009). Recent research has shown that the phototactic capacity some non-visual organisms exhibit suggests that ‘non-visual systems may have preceded visual phototactic systems in evolution’ (Randel and Jékely, 2016). As a result, this understanding has the potential to dismantle visual systems hegemony in which light, a natural agent embedded deeply in biblical symbolism and synonymity with the Enlightenment, is no longer exclusive to phenomenological understandings of world(s).
Furthermore, Gorostiza et al, in their paper argue for phototaxis to be ‘an iconic example for innate preferences.’ Rather than what scientists have acknowledged primarily as an evolutionary adaptation, phototaxis in Drosophila, a small fruit fly, evidences a ‘value-driven process’ — in other words a behaviour response that can be perceived as a ‘preference,’ an act holding agency. The article observes:
In their struggle for survival, animals do not just need the capability to trigger behaviours at the appropriate time, but these behaviours need to be flexible in response to or anticipation of changes in environmental and internal conditions. (Gorostiza et al, 2016)
Perhaps then it is to be noted that one of the greatest changes to natural environments in urbanised, contemporary cities is light pollution.
Light pollution, defined as ‘the presence of anthropogenic and artificial light in the night environment,’ (Wikipedia) really only became evident to scientists, according to the National Geographic, when ‘The World Atlas of Night Sky Brightness, a computer-generated map based on thousands of satellite photos, was published in 2016'.
The map shows how different continents, cities, towns and streets are lit by artificial light at night. Europe, Asia and the United States are radiating light in excessive amounts. There are very rare places such as in Siberia where locations of complete darkness can be found, whereas Singapore, Qatar and Kuwait are completely illuminated. The National Geographic notes:
Artificial light can wreak havoc on natural body rhythms in both humans and animals. Nocturnal light interrupts sleep and confuses the circadian rhythm—the internal, twenty-four-hour clock that guides day and night activities and affects physiological processes in nearly all living organisms.
As studies have tended to focus on the impact of light pollution lowering the levels of melatonin, the gland responsible for regulating sleep by responding to darkness of light, in the human body, researcher F J Verheijen proposes the term ‘photopollution’ instead to convey ‘artificial light having adverse effects on wildlife.’
Boyes et al (2021), provide a statistical summary of the global condition:
It is estimated that 23% of the world’s area experiences light-polluted skies (Falchi et al., 2016), and the global area that is artifically lit grew by 2% per year between 2012 and 2016 (Kyba et al., 2017). Urban green space, domestic gardens, and road verges are expected to be among the most frequently illuminated habitats, though light pollution is also encroaching into less human-influenced areas, including biodiversity hotspots (Guetté et al., 2019; Koen et al., 2018), as well as freshwater and marine systems (Perkin et al., 2011; Davies et al., 2014). […] Nocturnal and crepuscular species are expected to be most vulnerable to artificial light. More than 60% of invertebrates are estimated to be nocturnal (Hölker et al., 2010), including 75-85% of Lepidoptera (Kawahara et al., 2018).
As the article notes, moths most famously and most visibly respond to light pollution.
The popular adage, ‘like moth to a flame’ takes the form of a tempest beneath the anthropogenic artificial lights illuminating our anthropocentric world. The direction of the moth’s flight is completely halted and then re-direct towards the exuberant light source.
Vladimir Nabokov’s extensive lure set up to catch his night moths then perhaps seem futile today. In the his Russian poem, ‘Nochnye Babochki’ (1922), he writes:
For you,
moths I prepare a lure:
anticipating since morning a successful hunt,
I mix flat beer half and half
with armed molasses, then add rum.
And I go out into the garden, to its mists and wonders,
and I smear the damp oak trunk
with sticky gold, and juice drips from the brush,
trickles down into the cracks, gleaming and heady...
The saffron globe of the moon sails out from behind the cloud,
and the oak, my accomplice, looms tall and ample.
It has soaked up many an earthly dream;
I wait in the lilac gloom, and it waits with me.
A simple glance at an LED lamp-post and it all seems to go to waste. We no longer have to wait for the full moon as there is much more powerful source attracting the moths flight today. But it is not the singular ‘moth to a flame’ nor even the two or three rare species Nabokov finds on his ambrosia covered tree, rather in unprecedented numbers, numerous, countless moths swarm, in a brutal frenzy towards an artificially created ‘light’ - an unnatural death - and not the flame. How do we then look at the lamp post covered in the carcasses of the moth species?
The cloud of moths encircling the artificial light reveal a harrowing image into extinction today.
~ Vedika Rampal
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Cited Texts:
Boyes, D.H., Evans, D.M., Fox, R., Parsons, M.S. and Pocock, M.J.O. “Is light pollution driving moth population declines? A review of causal mechanisms across the life cycle.” Insect Conserv Divers, 14, (2021): 167-187. https://doi.org/10.1111/icad.12447
Gorostiza, E. A., Colomb, J., & Brembs, B. “A decision underlies phototaxis in an insect.” Open Biology, 6,12, 2016. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5204122/
Jékely, Gáspár. “Evolution of phototaxis.” Philosophical transactions of the Royal Society of London. Series B, Biological sciences vol. 364,1531 (2009): 2795-808. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781859/
Nabokov, Vladimir. “Nochnye Babochki” translated by Dmitri Nabokov. In Nabokov’s Butterflies, edited by Brian Boyd and Robert Michael Pyle, Boston: Beacon Press, (2000): 105-107.
National Geographic Society, “Light Pollution.” National Geographic, (2019) https://www.nationalgeographic.org/article/light-pollution/
Randel, Nadine, and Gáspár Jékely. “Phototaxis and the origin of visual eyes.” Philosophical transactions of the Royal Society of London. Series B, Biological sciences vol. 371,1685 (2016): 20150042. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685581/
Verheijen, F J. “Photopollution: artificial light optic spatial control systems fail to cope with. Incidents, causation, remedies.” Experimental biology vol. 44,1 (1985): 1-18. https://pubmed.ncbi.nlm.nih.gov/3896840/
Wikipedia contributors, "Light pollution," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php title=Light_pollution&oldid=1014222641 (accessed April 10, 2021).
Wikipedia contributors, "Phototaxis," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Phototaxis&oldid=1006769049 (accessed April 10, 2021).
