Insect biomass refers to the total weight of all insects in a specific area at a given time. This measurement provides a snapshot of the abundance of this diverse group of animals. Scientists study insect biomass to gauge the health of an ecosystem, as a stable insect population indicates a well-functioning environment, while changes can signal ecological disturbances. Understanding the collective mass of insects helps explain their combined impact on the environment.
The Roles of Insect Biomass in Ecosystems
The collective weight of insects in an ecosystem performs a variety of functions. Pollination is one of the most well-known services; bees, butterflies, moths, and some flies and beetles are responsible for fertilizing many of the world’s flowering plants, including human food crops. Without this activity, many plant species would be unable to reproduce, leading to consequences for entire plant communities and the animals that depend on them.
Insects are also nature’s primary decomposers, breaking down dead organic material such as fallen leaves, wood, and animal carcasses. This process of decomposition, carried out by termites, ants, beetles, and fly larvae, is for nutrient cycling. They unlock nutrients like nitrogen and phosphorus from dead matter, returning them to the soil where they can be used by plants and maintaining soil fertility.
The volume of insects makes them a foundational food source for a large number of other animals. Birds, bats, amphibians, reptiles, and various mammals rely on insects as a protein-rich part of their diet. A decline in insect biomass leads to food shortages that ripple up the food web, affecting predator survival. Even other invertebrates, such as spiders and predatory insects, depend on this abundant food supply.
Many insect species live in or move through the soil, and their activities contribute to its health. Burrowing insects, such as certain beetles and ants, create channels that aerate the soil and improve water infiltration. This enhances root growth for plants and reduces water runoff and soil erosion. Their tunneling mixes organic matter into the soil, further enriching it and supporting a healthy underground ecosystem.
How Insect Biomass Is Measured
Scientists employ several methods to estimate the total mass of insects in an area. After collection, samples are taken to a lab, sorted, dried to remove moisture, and weighed to determine the dry biomass. Common collection techniques include:
- Malaise traps, which are tent-like structures that passively intercept flying insects like flies and wasps over long periods.
- Pitfall traps, which are containers buried in the ground to catch ground-dwelling insects like beetles, spiders, and ants.
- Sweep netting, where a sturdy net is swept through vegetation to catch insects residing on plants, such as grasshoppers and caterpillars.
- Light traps, which use a specific wavelength of light to attract and capture nocturnal insects.
Observed Changes in Insect Biomass
Numerous scientific studies have documented significant declines in insect biomass. For example, a well-known study from protected nature areas in Germany revealed a major reduction in the biomass of flying insects over a 27-year period. These declines are not limited to one type of insect but have been observed across various groups, including moths, butterflies, bees, and beetles.
Patterns of change vary by region and insect group. While some areas show steep declines, others report more stable populations or even increases in certain species, such as aquatic insects in rivers with improved water quality. This suggests local environmental conditions play a large role in the fate of insect communities.
Changes also fluctuate yearly based on weather. For instance, biomass may increase during years with higher temperatures or specific rainfall patterns, demonstrating sensitivity to short-term environmental shifts. This variability underscores the complexity of tracking long-term trends and separating natural population cycles from human-driven changes.
Primary Drivers of Insect Biomass Fluctuation
A primary driver of change in insect biomass is habitat loss and fragmentation. As agriculture, urbanization, and infrastructure expand, natural landscapes are destroyed or broken into smaller, isolated patches. This process eliminates plants and resources insects need, reducing their populations and making it harder for them to move and interbreed.
The widespread use of pesticides in agriculture is another driver. Non-selective insecticides eliminate not only pests but also beneficial insects like pollinators. Herbicides destroy plants that many insects rely on for food and shelter. Even when not immediately lethal, these chemicals can impair insect reproduction, navigation, and immune responses.
Climate change pressures insect populations worldwide. Rising global temperatures can alter insect life cycles, causing them to emerge out of sync with their food plants or predators. Changes in precipitation, like more frequent droughts or floods, can destroy habitats and directly kill insects.
Pollution from various sources also affects insect biomass. Artificial light at night disrupts the behavior of nocturnal insects like moths. Chemical pollutants from industrial and agricultural runoff can contaminate water sources, harming aquatic insects. The introduction of invasive species can also disrupt ecosystems by outcompeting native insects for resources or preying on them.