Impact of agrochemicals on spider diversity in field margins

My diploma thesis is concerned with the impact of agrochemicals on spider diversity in field margins. In this context I observe the effects of separate treatments of a fertilizer, a herbicide and an insecticide and the combination of these three agrochemicals. In 2011, a field study was conducted on a meadow near Bad Bergzabern. The meadow was separated into 64 plots of 8 x 8 m and each treatment was replicated 8 times. The Sampling was performed at three different dates using a dip net. The most common spider family in my samples was crab spiders (Thomisidae). I could show declining density of juvenile crab spiders in different pesticide treatments. Insecticide exposure was the main reason for the decline in juvenile crab spider density. However, there is also a significant decline of juvenile crab spiders in plots, which were only treated with herbicide. The lowest density of juvenile crab spiders was recorded in plots treated with the combination of insecticide and herbicide.


Spiders are important and abundant predators with high diversity in different types of ecosystems. Spiders are distributed on the ground and in the vegetation and usually they wait for prey rather than hunt it actively. An example for highly specialized ambush predators are crab spiders (Thomisidae). They sit well camouflaged on leaves or blossoms and wait for their prey. After prey comes in range, it is caught with the anterior legs and paralyzed by injecting poison.


The potential of spiders as pest agents in agricultural ecosystems emerges more and more from different studies. However their value as biocontrol agents is often limited because spider densities are usually low in the agricultural landscape, due to the use of pesticides. Field margins can be an important refuge for spider populations, especially during winter while fields lie idle. They can also function as an origin for recolonisation of spider populations after pesticide application.


Due to pesticide drift and over-spraying, field margins are highly affected by agrochemicals. Therefore they may lose their function as habitat and refuge for spiders. Pesticides impact directly influence spider populations and communities in field margins and hence may affect species richness in agricultural landscapes. Therefore it is necessary to assess the impact of pesticide drift and over-spaying on spider communities and populations in field margins.


Marcus Metz

Dr. Carsten Brühl