Moths: Lost In The City's Light Pollution

Light pollution is a growing problem that has been documented to disrupt the behaviour of many animals, including nocturnal insects like moths. Moths are attracted to artificial light sources, which can lead to increased mortality through predation or exhaustion. Moths might expend a lot of energy trying to reach an artificial light source, potentially taking them away from food sources or refuge. Once they reach the light, they may become confused and circle it, leaving them vulnerable, exhausted, or trapped. Light pollution can also impact moth caterpillars, disrupting their development and life cycle. The effects of light pollution on moths can have consequences for the wider ecosystem, as moths play an important role in pollination.

Light pollution disrupts moth behaviour

Artificial lights can also impact the behaviour of moth caterpillars. Diapause induction is a process that moth caterpillars use to pause their development to wait for better conditions, such as waiting out the cold winter months. Excess light at night interferes with the visual cues that caterpillars use to tell the time of year, confusing this process and leading them to develop in conditions that are less than ideal.

Even dim artificial light in the form of skyglow can disrupt moth behaviour. Adult moths may not carry out their usual pollinating activities when drawn to artificial light, which could impact the plants their caterpillars rely on for food. Some studies also suggest that artificial light can affect the quality of the plants that caterpillars use for feeding and shelter. Changes in light conditions may alter the nutritional value of the plants, which may affect how well the caterpillars develop.

Artificial light affects moth reproduction

Artificial light at night can have a significant impact on moth reproduction, affecting both adult moths and their caterpillars.

Impact on adult moths

Moths are attracted to artificial light sources, which can disrupt their natural behaviour. Moths may spend a lot of energy reaching these light sources, taking them away from essential activities such as feeding, breeding, and laying eggs. This can leave them exhausted and less able to carry out their usual behaviours, impacting their ability to survive and reproduce.

Research has shown that artificial light can reduce feeding frequency in moths, with shorter wavelength radiation light (green light) having the most significant effect. This reduced feeding frequency can lead to shorter longevity and a reduced effective reproduction period in moths. It can also result in reduced fertility, as starved females of some moth species laid fewer eggs than well-fed females. Additionally, reduced feeding can decrease sex pheromone production and duration of pheromone excretion in female moths, reducing the attraction of males for mating.

Impact on moth caterpillars

Artificial light can also affect the life history and seasonal timing of moth caterpillars. For example, male caterpillars exposed to white light reached a lower maximum mass than those under red light or in darkness. They also pupated earlier and obtained a lower pupal mass, which can have negative consequences for their longevity, flight ability, and sperm competition. Since female body mass is strongly correlated with egg production, these effects on male caterpillars can have more severe fitness consequences for females.

Artificial light can also interfere with the initiation of pupal diapause in moth caterpillars. Diapause is a process where caterpillars pause their development to wait for better conditions, such as waiting out the cold winter months. Artificial light can disrupt the natural light-dark cycles that caterpillars use as cues for seasonal timing, leading to de-synchronisation of imago emergence and potentially high mortality during unfavourable seasons.

Overall, artificial light can have significant direct and indirect effects on moth reproduction, further contributing to the decline of moth populations.

Light pollution impacts moth predators

Light pollution has a significant impact on moth predators. Moths are naturally attracted to light sources, and artificial lights can confuse and disorient them. This makes them easy prey for nocturnal predators such as bats. The bright lights also attract a large number of moths, providing predators with a concentrated group of exhausted and vulnerable moths to feed on.

Moths' natural behaviour is disrupted by artificial lights, and they may spend a lot of energy trying to reach the light source. This leaves them tired and confused, circling the light, and unable to escape if a predator appears. The impact of light pollution on moths is a conservation issue, and it is important to raise awareness about its effects on these insects.

Research has shown that moth caterpillar numbers are significantly lower in areas illuminated by streetlights. A study in southern England found that streetlights reduced caterpillar numbers in grass verges by one-third and by almost half in hedgerows compared to unlit areas. Another study in Germany examined the physical traits of moths over 137 years and found that there was a trend towards smaller-eyed females in areas with medium to high light pollution.

Light pollution also affects the plants that moths rely on. Adult moths may neglect their pollinating duties when drawn to artificial light, impacting the plants that caterpillar moths feed on. Some studies suggest that artificial light can reduce the nutritional value of these plants, further endangering the moth population.

The effects of light pollution on moths and their predators are complex and multifaceted, and more research is needed to fully understand the impact of artificial light on these nocturnal insects.

Light pollution affects moth plants

Light pollution not only affects moths but also the plants that depend on them for pollination. Moths are one of the most important nocturnal pollinators, but artificial light at night disrupts their pollinating activities.

Moths are attracted to artificial light sources, which can be disorienting for them. Moths may expend a lot of energy trying to reach the light source, taking them away from their usual activities such as feeding, breeding, or laying eggs. This can impact their ability to survive and thrive. Once moths reach the light source, they may become confused and circle it, leading to exhaustion or entrapment. Exhausted or disoriented moths are less able to carry out their normal behaviours, further impacting their survival.

The decline in moth populations due to light pollution can have a ripple effect on the plants they pollinate. Adult moths may neglect their pollinating duties when drawn to artificial light, which could reduce the reproductive success of the plants their caterpillars rely on for food. Studies suggest that artificial light can also affect the quality and nutritional value of these plants, potentially impacting the development of caterpillars that feed on them.

The impact of light pollution on moth plants is a growing concern, as moth populations have already been declining in recent decades due to habitat loss and climate change. Reducing light pollution is crucial for the survival of moth populations and the ecosystems that depend on them, including various plant species.

Overall, light pollution has indirect but significant effects on moth plants by disrupting the natural behaviour and activities of moths, which are essential for the health and reproduction of certain plant species.

Light pollution affects moth morphology

A 137-year study in Germany examined the body length, eye size, and forewing length of the moth Agrotis exclamationis, a common species in the Berlin-Brandenburg region, which offers a range of light pollution levels. The study predicted decreasing forewing length, body size, and eye size in response to increasing light pollution. While no trait differences were observed along the spatial gradient, there were trait and sex-dependent changes along the temporal gradient.

Light pollution can also impact the development and life cycle of moths. Many insects, including moths, use day length to synchronize their life cycle with the changing of seasons. Shortening late summer days trigger the transition to the overwintering state for pupae. However, light pollution can disrupt this process, leading caterpillars to interpret the days incorrectly and causing them to immediately develop into adult moths. These moths, misled by artificial light, may not be able to successfully reproduce or survive the winter.

Additionally, light pollution can reduce moth populations by impacting their feeding, breeding, and egg-laying behaviours. It can also make moths more vulnerable to nocturnal predators, further contributing to their decline. Overall, light pollution has multifaceted effects on moth morphology and behaviour, and it is important to address this issue to protect moth populations and the ecosystems they support.

Frequently asked questions