7.1 Prey deception in australian crab spiders  (Page 5/7)

In a study performed by Astrid Heiling et. al in 2005, yellow spiders were overwhelmingly found on yellow plants (93.7%, N=16), while white spiders were found on primarily white plants (69%), but also on yellow plants of the same species (31%, N=71). In order to test this pattern of distribution, the researchers conducted a choice experiment where it was found that spiders actively choose flowers, as opposed to just settling on what is available. They found that spider preference was due to reflectance properties of flowers. So why do yellow spiders overwhelming prefer yellow flowers, and white spiders have less of a preference? The researchers did further analysis of spider and flower coloration and by looking at reflectance and contrast found that while the white spider on white plant combination was visible by bees, the yellow on yellow pairing of the two species yielded a higher contrast. In fact, the yellow spider on a yellow plant combination yielded higher UV contrast than a yellow spider on a white flower! The combination of yellow spiders on yellow flowers and white spiders on either color of flowers are attractive to honeybees and correspond to the combinations that spiders choose most frequently. This shows that spiders are actively seeking to contrast highly with their background on the basis of perceived honeybee attraction (Heiling et. al, 2005).

Table 1. Overview of the color contrasts between white and yellow T. spectabilis and white and yellow C. frutescens , and the visibility of this contrast by honeybees. Modified from Heiling et. al, 2005.

Beyond picking the right flower in comparison to their body to create a desired level of contrast, spiders can manipulate other variables, such as their position on a given flower, to attract their hymenopteran prey. In another experiment performed by Heiling et. al, researchers placed spiders on both the ligulate florets and the center of daisies to see how honeybees would respond. Expecting that spiders positioned naturally on the petals would deceive honeybees while those placed atypically in the center of the flowers would repel the prey, researchers found their predictions to be supported. Researchers hypothesized that the honeybees may have been less attractive to daisies with spiders over the center because it would make it more difficult for spiders to access their reward (i.e. nectar). Another hypothesis was that the spider-covered centers had inflorescences that did not visually resemble natural daisies, hence the rejection by honeybees. What was evident, however, is that deception by spiders and attractiveness to honeybees was greatest when spiders were placed on the petals, a behavior that spiders exhibit in nature. In this careful choice, spiders are able to position themselves to influence the behavior of their hymenopteran prey (Heiling et. al, 2006). This adds to a bevy of evidence that confirms that spiders act in a way that maximize their attractiveness to prey.