Do insects live more during the day or at night? It is a question that has puzzled scientists for centuries. Australian researchers have now come up with the answer and call it a ‘groundbreaking’ study.
For the first time, insect activity worldwide has been mapped during the day and at night. “Our extensive research allowed us to finally provide the definitive answer to the age-old question of whether more insects are out and about at night or during the day,” says researcher Mark Wong of the University of Western Australia. And it turns out: insect activity increases by a third on average throughout the world at night. But the differences between insects are great. For example, it matters whether they live in water or on land, in the tropics or on the savannah.
Difficult field research
You would think that it has already been determined how active insects are or are not at night, but that is more difficult than expected, because commonly used methods for field research are not suitable. For example, with trawl nets you only catch inactive insects, while light traps do not work as well during the day as at night, which can result in a distorted image.
The researchers got around this problem by looking only at studies where samples were collected both during the day and at night with traps that specifically catch moving insects, such as pitfalls and drift nets in the water.
From the jungle to the rivers
They have worked through thousands of studies to ultimately arrive at 99 suitable studies, which were carried out between 1959 and 2022. In total, more than 3 million insects have been observed in various areas, from the tropical jungle to more northern forests and from arid grasslands to ecosystems in sea.
And this resulted in a number of interesting conclusions, which the researchers discussed Nature published. There are many groups of insects, such as mayflies, caddisflies, moths and earwigs, that are mainly active at night, while there is more activity during the day from bees, wasps, beetles and ants.
Nocturnal activity was also more common in rivers and streams. More than twice as many insects appeared to be active in the water at night. That was different on land. There was generally more activity there during the day. Especially in grasslands and savannahs, the number of insects flying or tripping during the day could be three times as many as at night.
Better not eaten
This difference between land and water insects probably has a common cause for any animal behavior: they want to avoid predators. “Fish hunt insects during the day, while nocturnal animals such as bats make life on land more dangerous at night,” said Wong.
But the temperature also plays a role. “We discovered that insect activity peaked at night in the warmer areas of the world, because the animals probably flee from the heat during the day,” thinks the scientist, who immediately warns about the dangers of global warming.
Less warm
“In the hottest areas of the world, such as the tropics, warming further reduces the activity of nocturnal insects, which already struggle with the heat. Moreover, artificial light is also harmful to nocturnal animals. It disrupts their natural behavior within the ecosystem they live in.”
We have to do something about that, because we really can’t live without insects. They are needed for plant pollination, nutrient cycling and pest control. They do many of these tasks at night, when they are more active.
Scientific adventure
It is therefore very important to continue doing field work and better understand what insect activity looks like, says Wong. “Such research can be exhausting, because you have to install and replace the traps in many different locations several times a day. But it is extremely valuable. Insects are among the most diverse and important organisms on our planet. Studying their complex rhythms is not only a scientific adventure, but also necessary to preserve biodiversity on a planet that is changing so quickly.”
