Urban Moths Develop Smaller Wings in Response to Light Pollution; Interrupted Flight Speed Makes Them Vulnerable to Predators

Artificial lights at night disrupt the lives of many insect species. They are either diverted from their habitats and mates or exposed to predators. Ecological changes brought by light pollution are also assumed to cause evolutionary changes in some insects.

(Photo: Wikimedia Commons/ Mathias Krumbholz)

Threats from Light Pollution

Urbanization is one of humans' ever-increasing impacts on the environment. According to the United Nations' 2018 Revision of World Urbanization Prospects, about 68% of the global population will live in urban areas by 2050.

This trend is expected to drive strong expansion of the urban land area, which can go hand in hand with the deterioration of environmental quality. Diverse processes, such as light pollution, can cause this.

Artificial light at night (ALAN) has been shown to affect nocturnal insects in two ways. First, it alters their day-night cycles, which could disrupt life cycle regulation and plant-pollinator interactions. Second, many insects suffer from the negative consequences of their phototaxis, causing them to be repelled or attracted by ALAN.

As a result, the insects are driven away from their favorable habitats, resulting in higher predation risk. In addition, nocturnal insects are distracted or restrained from important behaviors such as reproduction and foraging. Such changes lead to ecological alteration and can also serve as agents in driving rapid evolution.

Evolutionary Implications of ALAN

Experts from various institutions in Belgium and Switzerland investigated the body and wing sizes of hundreds of moths captured in a prior scientific study. Their findings are discussed in the paper "Evolutionary change in flight-to-light response in urban moths comes with changes in wing morphology."

In the earlier experiment, scientists gathered 680 larvae of live ermine moths (Yponomeuta cagnagella) in brightly lit cities and dark rural settings. Both groups were raised in the same test area. After growing to adulthood, each group was tested in terms of their response to a light source at night. It was found that 30% fewer urban moths were captured in a light trap.

For the new study, the research team led by Evert Van de Schoot measured the wing and body size of all the moths tested in the prior experiment. It was found that the city moths had slightly smaller wings than those captured from the rural areas. It was noted that the smaller wing size is related to weaker response to the light test.

According to the researchers, the smaller wings of moths could affect their flight speed and distance. Both of these could have an impact on the way the moths obtain their food. They also noted that a trade-off to smaller wings in urban settings could enable moths to survive if it meant lesser attraction to artificial light sources, which seem to prevent the insects from feeding and make them more vulnerable to predators.

De Schoot and his team acknowledged that they could not find any direct connection between light pollution and smaller wings. They also considered other urban factors that could have played a role, like the various types of food sources or the more fragmented environment found in urban areas. Furthermore, they theorized that the city moths could be experiencing changes to their vision or how their brains process the environment because they thrive in constantly lit areas.