The special function of many species in the stability of the ecosystem is not well known, nor is it known how many insect species are endangered by man's impact on the natural environment. Estimates of the number of species of insects vary from 700,000 to 2 million. They represent about 80% of known animal life and are very widespread and adaptable. In the temperate zone for example, an average acre of soil may have over 4 million insects. Only a few thousand species are such as to affect man's activities in a manner which requires some form of control measures.
A well-documented German study, released in the journal PLOS One in 2017, revealed that in the last 27 years, the flying insect biomass measured in protected German nature reserves declined an average of 76%, with an 82% drop during the midsummer season, when insect populations should be thriving. Another study found that Germany experienced a 15% drop in its bird population over the last decade. Clearly, an insect collapse also affects the birds who feed on them.