Insects at Night
From the Bee City Committee
Support our insects at night
We tend to think about protecting our insects when and where we see them. This is perhaps why we may have a higher propensity to think about protecting pollinators we can see flying around than organisms that live in the darkness of the soil or hidden in the leaf litter. In this article, we would like to bring some attention to other groups of insects we may tend to forget about, but which we can also help protect: insects that are active in the night.
Don’t insects sleep at night?
Although many insects are generally less active at night due to the lower temperatures and their inability to move when the temperatures drop below a certain threshold, many insects are adapted to being active in the night. For example, if they are pollinators of nocturnal or dusk flowering plants such as several moth species are, they will be active when darkness falls. Other insects are active at night as predators, or at certain times of the season looking for mates and egg laying sites. For all these insects, the absence or reduced presence of light are important for allowing them to take on what they need to do to survive and/or reproduce. For this reason, the presence of artificial night lighting in our outdoor spaces, especially in the warmer periods of the season, can interfere with these insects, leading to potentially very negative effects.
How can outdoor night lighting affect nocturnal insects?
Insects can be perturbed in different ways through outdoor night lighting. One of them is its potential interference with their temporal rhythms. In fact, like most animals, insects use light-darkness and the presence of certain night sky cues (e.g., full moon) to regulate their developmental cycles and perceive the progression of the season. The presence of supplementary lights during the night hours can lead to altered developmental cycles, making them longer or mismatching those of other conspecifics. This can lead to the insects missing their optimal mating times, losing their ability to forage on specific plants, or to properly prepare for the arrival of colder nights as the season progresses.
The use of often non-essential lighting such as light strings and other nocturnal accent lights in our spaces can negatively affect the development, survival and reproduction of many nocturnal insects.
Photo: P. Danilyuk (CC).
Another issue that artificial nocturnal light can produce relates to the spatial disorientation of nocturnal insects. This can occur when insects are attracted to nocturnal sources of light instead of moving towards their optimal habitat. This can lead to increased predation in those areas (the insects become more exposed to being seen), as well as their spending valuable energy by spending time in an inhospitable region. Further, disorientation can happen in a more indirect way, by the light’s interference with the patterns present in the canopy. In fact, many insects have been shown to use the contrast pattern of the canopy and the sky to navigate and identify optimal habitat. The presence of nocturnal artificial lights can lead to the disappearance or a stark modification of that contrasting pattern, interfering in their ability to find their way in the ecosystem, and decreasing their ability to find proper habitat for their survival.
Some insects like fireflies use bioluminescence for inter-species recognition and mating. Photo: T. Ota
In some cases, the presence of nocturnal artificial light can lead to interference in mating and intraspecific recognition behaviors. Many groups of insects, such as fireflies and glow worms, use light cues to attract and recognize each other. In regions such as ours, where fireflies represent such an important part of our ecosystem, the use of outdoor nocturnal artificial lighting can interfere with the finding of mates and can potentially lead to much reduced abilities to reproduce and sustain populations.
What can we do to reduce this type of nocturnal pollution?
The obvious answer is that if we want to reduce this type of pollution, our best bet is to turn off non-essential outdoor night lights, in particular during times of the year when insects are active. Doing this may actually save us some money, but also will allow us to support a higher diversity in our area, all while potentially letting us appreciate even more the nocturnal activity that may be present in our region. For example, doing this may make it easier to support fireflies and participate in their conservation, but can also support the reproduction of plant species that depend on nocturnal pollinators.
If leaving lights on is unavoidable, one should consider the intensity that is being used. Can the light be dimmed to a lower intensity? Could it be filtered to display a color that is less disruptive to insects? The Xerces Society has put together a really neat guide on this, and we encourage you to consult it.