Spiders are beneficial inhabitants of agricultural fields because of their important contributions to biological control of pest insects; consuming tons of small arthropods every year.
Spiders eat anything they can catch, even prey larger than themselves.
When abundant, spiders contribute to the control of many insect pests in Arizona crop fields including whiteflies, lygus, fleahoppers, and lepidopteran larvae.
Field studies in Arizona demonstrate that the crab spider, Misumenops celer (Family Thomisidae) and Dictyna spider, Dictyna reticulata (Family Dictynidae), are common in Arizona cotton fields and can be influential predators.
Unlike other spiders that spin webs to capture food, crab spiders rely on stealth and surprise. This spider actively searches plant surfaces, litter, and debris for prey. They hide in flowers or foliage and ambush the prey.
Their common name derives from the fact that they look like and walk like crabs. Dictyna are small, brownish, web-making spiders that trap whitefly adults and other insects in their webs. Examining their webs enables easy identification of the whitefly species in the field (sweetpotato or banded-winged).
Jumping spiders (Family Salticidae) are generally less abundant in cotton fields but, like crab spiders, ambush the prey. Jumping spiders have stout bodies and long front legs adapted for jumping, plus four pairs of eyes with one very large set in the middle of the face.
All species inhabiting cotton and other Arizona fields are part of a “food web.” This flexible and resilient web encompasses all predators and parasitoids that utilize other species and sometimes each other for food.
Arizona research suggests that crab and Dictyna spiders can be very important in the natural control of many insect pests in cotton and other field crops, especially in conjunction with selective insecticides.
Overall, spiders are important components of natural and agricultural ecosystems and are good indicators of ecosystem health and natural control dynamics.
For photos of these spiders, go online to: http://ag.arizona.edu/crops/cotton/files/SpidersWebsvFc.pdf.