SNPA Strapline

Seeing Stars

Trawsfynydd (© Keith O'Brien)

alt=Ty Cipar Llyn Conwy (© Keith O'Brien)


Most animals are sensitive to light, and light and darkness greatly influence their environment.

Since time immemorial, night and day have turned continuously on Earth as it orbits the sun. Consequently, most species have evolved to adapt to these conditions and can now be divided into those that are active during the day (the diurnal species) and those that are active at night (nocturnal species).

But, did you know that 60% of vertebrates and 30% of invertebrates are nocturnal species? At night they'll find food, mate, migrate and communicate. It is therefore important to ensure that their environment is suitable for them to live successfully by reducing light pollution.

How does light pollution impact on our natural world? Here are some examples:

  • Many of our birds use the sun, moon and stars to navigate from place to place. Consequently, migrating birds can get lost if they are attracted to areas that are lit.
  • Artificial lighting at night impacts on songbirds’ ability to sire, lay and sing at dawn.
  • Street light will affect the ability of the Atlantic salmon smolts to migrate.
  • Strong light during the night confuses some bat species that are sensitive to light. They think that night is day and to avoid being hunted, they don’t feed
  • Strong lights at night also confuses bats, particulalry when shone onto ecologically sensitive areas such as commuting corridors, roost entrances or feeding areas.
  • For some bats, the result of light pollution is that they have less time to forage, which in turn entails less food. They fly further for less food which ultimately effects their health and fitness.
  • Too much light can impair nature’s ability to recognise the duration of a day as the seasons change – it can interfere on tree budburst and leaf-fall, flowering in plants and breeding in birds.
  • Excessive light pollution can affect the reproductive process of aqua-insects such as stoneflies, caddisflies, and mayflies. These insects are critical to the freshwater ecosystem, and an important source of food for birds, fish and other animals.
  • Light reflecting brightly on a shiny surface attracts aqua-insects to lay eggs there rather than in the water.
  • There is evidence that the number of glow-worms are declining in Britain. One reason for this decline is that there is less opportunity for glow-worms to mate due to high levels of light pollution, as the males are attracted to artificial light rather than the female glow-worms.
  • Butterflies have larvae that feed at night, but in artificial light, they are more likely to be hunted, thus leading to population declines.
  • Many species of insects have evolved such that they use moonlight to see where they are i.e. moths. Therefore, artificial lighting (including light from the UV spectrum) can adversely impact on such species by disrupting their natural navigation systems.
  • It is believed that as many as one third of insects that are attracted to artificial lights are killed - by hitting against the hot lamps, by being confused, or tired.
  • Usually at night moths pollinate flowers and artificial light can confuse the colour of flowers.

Although insects, sometimes, can be a nuisance for us, they are extremely important for many food chains. One in three of every mouthful of food we eat depends on insect pollination.

Death's-head Hawkmoth

Death's-head Hawkmoth (Acherontia atropos) (© SNPA)


Damselfly (Ischnura_heterosticta)

Creatures that are attracted to artificial light: moths, beetles, lacewings, aphid, caddis flies, crane flies, midges, hoverflies, true flies, damselflies, ant-lions, great green bush cricket, and wasps.

Without insect pollination, 8 out of 10 wildflowers could disappear.

Together with the negative elements of climate change, land use changes and loss of habitats, light pollution has a detrimental effect on our ecosystems.

Therefore, please help us to conserve biodiversity in Snowdonia;
Think before switching on:
The right light, in the right place at the right time?