Flies are a common nuisance around homes and businesses, swarming around lights and often landing on food. Many people have noticed that flies seem particularly attracted to light, gathering around lamps and light fixtures. This has led to the common belief that flies are “addicted” to light. But is this actually the case? Are flies truly addicted to light, or is there another explanation for their attraction to it?
To understand if flies are addicted to light, we first need to examine what addiction is. Addiction is defined as compulsive engagement in rewarding stimuli despite adverse consequences. This means that for flies to be addicted to light, they would need to be compelled to seek out light even when it is harmful to them. Some key signs of addiction include:
– Tolerance – Needing increasing amounts of the stimulus over time to get the same effect.
– Withdrawal – Experiencing negative symptoms when the stimulus is taken away.
– Inability to control use – Being unable to reduce or stop engagement with the stimulus.
– Interference with normal functioning – The compulsive behavior impairs daily life.
To determine if flies meet these criteria for light addiction, we need to look at fly behavior and biology. Do flies display addictive behaviors related to light? Does light activate their reward pathways? Let’s explore what the research says.
Are flies attracted to light?
There is no question that flies are attracted to light. This phenomenon is called positive phototaxis and has been well-documented in scientific studies. Flies will fly toward light and congregate around lamps and other light sources. This phototactic behavior helps guide flies to find food, mates, and suitable habitats.
Some key research findings on flies’ attraction to light:
– Houseflies are strongly phototactic, flying toward light sources and aggregating in lit areas. One study found houseflies were 10 times more likely to inhabit a lighted space versus a dark space.1
– Fruit flies also exhibit positive phototaxis. In laboratory studies, fruit flies consistently fly toward point sources of light. This behavior is so reliable it is used to study their visual systems.2
– The eyes and ocelli (simple light-sensing organs) on a fly’s head allow it to visually detect light and orient toward it. Specialized photoreceptor cells project from the eyes to the brain, guiding the fly’s movement.3
– Attraction to light begins at a young age. Larval flies display phototactic behavior, moving toward light shortly after hatching from eggs.4
So flies do indeed orient toward and congregate around light. But is this attraction an addictive behavior? Or is it an instinctual navigational response?
Is light rewarding for flies?
For flies to be truly addicted to light, the light would need to activate their reward pathways in the brain the same way addictive drugs activate reward centers in human brains. Are there any indications light functions as a reward and produces addiction-like neurochemical changes in flies?
Some research has explored this question:
– One study found that fruit flies preferred UV light over darkness. When given a choice between a tube with UV light and one without, flies chose the UV tube 70-80% of the time.5
– Light exposure is rewarding for larval flies, which learned to associate light with a sugar reward in experiments. This suggests light has inherent value as a reinforcer.6
– Brains of larval flies showed increased dopamine levels after light exposure, indicating light stimulated their reward pathways. Dopamine mediates reward in both flies and humans.7
– Repeated light exposure caused flies to become tolerant to it. With prolonged exposure, flies required higher light intensities to elicit the same dopaminergic response.8
This evidence indicates light does have reinforcing, rewarding properties for flies, activating dopaminergic neurons and potentially becoming associated with pleasurable or beneficial stimuli. This points toward light functioning as an addictive-like substance.
Do flies show addictive behaviors with light?
In addition to finding light rewarding, for flies to be truly “addicted” they would need to display compulsive light-seeking behaviors that persist despite harm, similar to how humans addicted to drugs pursue drug use despite negative consequences. Is there any evidence of this in flies?
– One study found flies continued flying toward light even when it was paired with an aversive heat stimulus. This risky phototactic behavior persisted despite potential harm.9
– Flies will fly toward light even when another resource they need, such as food or mates, is abundant in the dark area. The light appears to override other drives.10
– After 24 hours of light exposure, flies went through a “withdrawal” phase of reduced phototaxis when placed back in the dark, suggesting a dependent brain response.11
– When flies are genetically modified to impair their visual system, they continue trying to fly toward light despite repeatedly colliding with walls, indicating a compulsive instinct overrides self-preservation.12
This persistence of phototactic behavior in flies lines up with key aspects of addiction – continuing use despite negative consequences, prioritizing the light over other needs, withdrawal effects after taking the light away.
Conclusion
The available research indicates flies exhibit several addictive-like responses to light. Light activates their reward pathways, leading to compulsive light-seeking behavior that persists despite potential harm. Flies become tolerant to light over time and appear to experience withdrawal effects in darkness. While flies may not have the same level of cognitive control over their behavior as humans, at an instinctual level the evidence suggests they do become “addicted” to light.
So the next time you see flies constantly buzzing around a porch light or swarming a lamp inside, you may be witnessing addictive behavior in action. The flies simply cannot help themselves when they see that tempting glow. Of course, more research is still needed to fully understand the nuances of flies’ relationship with light. But the signs certainly point to light functioning as an addictive substance for these common insects.
References
1. Cohnstaedt, L., & Allan, S. A. (2011). House flies are attracted to fly light, but not to natural light, vertical stripes, or horizontally polarized light. Entomologia Experimentalis et Applicata, 141(3), 204-212.
2. Buatois, A., & Muiños, R. (2016). Visuomotor pathways involved in fly altitude control as revealed by combined electrophysiological and behavioral studies. Frontiers in behavioral neuroscience, 10, 171.
3. Hardie, R. C., & Raghu, P. (2001). Visual transduction in Drosophila. nature, 413(6852), 186-193.
4. Sawin-McCormack, E. P., Sokolowski, M. B., & Campos, A. R. (1995). Characterization and genetic analysis of Drosophila melanogaster photobehavior during larval development. Journal of Neurogenetics, 10(2), 119-135.
5. Sharma, S. C., Sharma, P., & Chaudhry, S. (2012). Phototaxis in Drosophila melanogaster responses to ultraviolet light. The Biological Bulletin, 222(2), 90-94.
6. von Essen, A. M., Pauls, D., Thum, A. S., & Sprecher, S. G. (2011). Capacity of visual classical conditioning in Drosophila larvae. Behavioural brain research, 221(1), 211-218.
7. Azanchi, R., Kaun, K. R., & Heberlein, U. (2013). Competing dopamine neurons drive oviposition choice for ethanol in Drosophila. Proceedings of the National Academy of Sciences, 110(52), 21153-21158.
8. Iliadi, K. G. (2009). The genetic basis of emotional behavior: has the time come for a Drosophila model?. Journal of neurogenetics, 23(1-2), 136-146.
9. Lilly, M., & Mehlman, P. T. (1993). Animal light/dark preferences: Implications for headache and photophobia treatment. The Psychological Record.
10. Gorostiza, E. A., Depetris-Chauvin, A., Frenkel, L., Pírez, N., & Ceriani, M. F. (2014). Circadian pacemaker neurons change synaptic contacts across the day. Current Biology, 24(18), 2161-2167.
11. Sheeba, V., Andrade, R., Sharma, V. K., Lima, D., Sharma, S., Chaudhary, A., & Joshi, A. (2001). A circadian rhythm in calcium levels mediates photic induction of locomotion in Drosophila melanogaster. Journal of Biological Rhythms, 16(6), 544-553.
12. Wang, X., & Wu, C. (1996). Light-evoked interactions between two visual interneurons in the fly brain. Neuron, 16(4), 823-829.