Ineffective crypsis in a crab spider: a prey community perspective

Area of Science:

• Ecology
• Behavioral Ecology
• Evolutionary Biology

Background:

• Cryptic coloration is theorized to benefit predators by increasing encounters with prey.
• Field studies investigating this hypothesis, particularly concerning ambush predators and their prey encounter rates, are scarce.
• The crab spider Misumena vatia offers a unique model, possessing the ability to alter its body color to match its floral hunting background.

Purpose of the Study:

• To empirically test the long-held assumption that cryptic coloration enhances predator success in a natural setting.
• To quantify the relationship between a crab spider's color-matching ability and its prey encounter and capture rates.
• To investigate the influence of spider crypsis on flower visitor behavior, testing hypotheses of crypsis, predator avoidance, and prey attraction.

Main Methods:

• A manipulative field experiment was conducted using the crab spider Misumena vatia and various flower backgrounds.
• A complete factorial design created six distinct color combinations of spiders and flowers, varying the degree of color-matching.
• Continuous video recording captured spider foraging activity and interactions with flower visitors, including insects like bees and flies.

Main Results:

• Flower visitors exhibited differential responses: some, like solitary bees, avoided spiders irrespective of camouflage, while others, like bumblebees, showed indifference.
• Contrary to the crypsis hypothesis, color-matched spiders did not achieve higher encounter or capture rates compared to visually conspicuous spiders.
• The study rejected the crypsis and flower visitor attraction hypotheses, providing strong support for the spider avoidance hypothesis and revealing prey indifference.

Conclusions:

• Background color-matching does not enhance ambush predator success (Misumena vatia) in terms of prey encounter or capture rates.
• Prey behavior, specifically avoidance or indifference, significantly influences the effectiveness of predator crypsis, challenging traditional assumptions.
• Understanding the ecological role of predator background matching requires a community-level approach, considering prey size, sociality, and predator-prey interactions.