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Abstract

The current global decline of insects will have profound cascading effects as insects serve numerous roles in ecosystems. Effective but simple methods are needed to describe spatial and temporal distribution of flying insects in detail. This applies especially to important but short-lived phenomena such as insect swarms. We developed, tested and implemented a non-invasive unbiased method with camera transects to measure spatio-temporal fluctuations in the abundance of nocturnal flying insects in different habitats. To test the sensitivity of the method, we then tested for the influence of environmental factors on this abundance. Our results show that the method is useful for the temporal and spatial comparison of insect abundances. Astonishingly, over 90% of the 63,180 photos lacked insects. We found profound differences in insect abundance and dynamic changes between the studied habitats. Photos with a large number of insects were rare, but occurred predominantly during the warmest period (June/July) and shortly after sunset. Our findings emphasize the importance of quantifying the dynamics of flying insects at a high spatio-temporal resolution. This method can be expanded to monitor long- and short-term changes in nocturnal insect abundance even at continental scales. With proper development, the camera transects we describe could be used for insect monitoring similar to the way camera traps are used to monitor terrestrial vertebrate populations, and could become an important tool for addressing the current mass disappearances of insects.