How Do Insects' Day and Night Activity Patterns Differ from the Equator to High Latitudes?

As the most abundant and functionally diverse group of animals on Earth, insects form a fundamental part of ecosystem functioning, and the way they distribute their activity across the 24-hour cycle is central to that role. As early as the 19th century, naturalists had already noticed the differences between organisms active during the day and those active at night, and they also recognized the striking rise in biodiversity and vitality when moving from temperate regions toward the tropics. Only in more recent ecology, however, have diel activity patterns been treated as an important mechanism of ecological differentiation. By being active at different times of day, species can reduce competition, avoid predators, and make more efficient use of resources. In this sense, temporal partitioning, much like spatial niche partitioning, helps maintain the coexistence of multiple species.

One study compiled data from 60 insect communities distributed around the globe, spanning both tropical and temperate regions and including diverse groups such as beetles (Coleoptera), flies (Diptera), and wasps, bees, and ants (Hymenoptera). Species were classified into three categories according to their activity timing: diurnal, nocturnal, and cathemeral. This framework was used to compare how insect communities partition time across different parts of the world.

As latitude increases from the equator toward the poles, the proportion of nocturnal insects within communities gradually declines. Near the equator, nocturnal insects make up about 36% of species in a community, but by 60° north or south latitude, that proportion drops to around 8%. In contrast, the proportion of cathemeral species shows the opposite pattern, increasing from roughly 18% at the equator to about 68% at higher latitudes. Diurnal species, by comparison, do not show a significant change in proportion across latitude. This suggests that latitude does not affect all activity strategies equally, but instead imposes very different selective pressures on nocturnal and cathemeral lifestyles.

Proportions of diurnal, nocturnal, and cathemeral insects across gradients in mean annual temperature (a) and temperature seasonality (b)（圖片來源：Wong MKL. (2025)，採用 CC BY 4.0 授權）

These findings are also consistent with earlier studies on mammals and reptiles. This cross-taxonomic consistency suggests that the environmental gradient represented by latitude may shape temporal niches in broadly similar ways across very different evolutionary lineages.

When considering the mechanisms behind this latitudinal gradient, temperature is thought to be one of the main drivers. As ectothermic animals, insects rely heavily on environmental temperature to regulate their physiological activity. In tropical regions, daytime temperatures often approach or even exceed the upper thermal limits of many insect species. Under such conditions, shifting activity into the night becomes an effective and often necessary form of behavioural regulation.

However, this pattern reverses as one moves toward higher latitudes. In temperate and colder regions, nighttime temperatures are often too low for efficient activity, causing many species to shift toward diurnal or cathemeral schedules in order to exploit the warmer daytime hours. Cathemerality in particular provides a highly flexible temporal strategy, allowing species to forage and reproduce whenever temperatures are favourable.

In addition to mean temperature, high-latitude regions are characterized by strong seasonal variation, meaning that the amount of usable activity time can fluctuate greatly over the course of a year. In such environments, highly specialized diurnal or nocturnal strategies may be too rigid to cope with rapidly changing conditions. By contrast, cathemeral species, with their greater temporal flexibility, may be better suited to unstable climates. The study indeed found that communities experiencing greater temperature seasonality also tended to contain a higher proportion of cathemeral species.

Beyond physical environmental factors, biotic interactions may also contribute to these patterns. In tropical regions, species diversity is extremely high, and competition for resources is correspondingly intense. Strong competitive pressure may drive species to become more temporally specialized, resulting in a greater number of strictly diurnal and nocturnal species that minimize overlap with one another. In temperate regions, where diversity is generally lower and competition may be less intense, species may be more likely to adopt broader activity schedules, increasing the prevalence of cathemeral strategies.

Predation may also play a role. Tropical ecosystems tend to support a greater abundance and diversity of predators, particularly visually oriented predators active during the day. Under such conditions, shifting activity to the night may reduce the risk of being eaten. In fact, some studies have shown that insects experience significantly lower attack rates at night, making nocturnality an effective defensive strategy. This may help explain why tropical communities tend to contain a higher proportion of nocturnal insects.

The timing of insect activity across the day has direct consequences for key ecological processes such as pollination, herbivory, decomposition, and nutrient cycling. When human activities alter light conditions, temperature regimes, or chemical environments, these temporal patterns may also be disrupted, potentially triggering cascading effects throughout ecosystems. Understanding these basic patterns is therefore important not only for explaining how insect communities are structured, but also for predicting and mitigating the consequences of ongoing human-driven insect declines.

Author: Shui-Ye You

Reference:

Wong MKL. (2025). Latitude shapes diel patterns in insect biodiversity. Biol Lett.