Signal Interactions between Crab Spiders, Flowers, and Bees

Astrid Heiling was a postdoctoral fellow with Marie Herberstein, supported on a grant that Herberstein, Lars Chittka, and I held. Heiling is an expert on crab spiders. Herberstein is an expert on the signals and behaviours of spiders. Along with Lars Chittka, we collaborated on the predator-prey relation between crab spiders and bees.


This crab spider, Thomisus spectabilis, is Australian. Crab spiders are ambush hunters. They sit on flowers and wait for prey to arrive. It is thought that their bodies are coloured to attract prey such as honeybees. Honeybees are an introduced species in Australia, but prove to be a popular prey for T. spectabilis. Heiling, Herberstein, and Chittka have shown, in a 2003 Nature paper, that bees prefer a flower with a crab spider on it over one with no spider. Further work shows that this preference turns to aversion if the crab spiders do not reflect in the UV range (Heiling et al., 2005a). UV reflection can be blocked by applying a suitable chemical.

Another way to increase prey capture is to choose flowers that bees are more likely to visit. We tested this hypothesis by letting crab spiders choose between pairs of randomly selected daisies to sit on. We then presented the same pairs for bees to choose. We found that the spiders and the bees tend to choose the same flower of a pair, about 75% of the time.

How do bees and spiders choose flowers? The odours of flowers are implicated. In one experiment, we covered the flowers with transparent plastic, and presented pairs for spiders and bees to choose again. The transparent plastic only cuts down light reflectance of all wavelengths slightly, but it cuts out smells drastically. This time, the bees and the spiders agree at chance levels.

The colours of flowers, however, also matter to crab spiders. They can be choosy about which colour of flower they sit on. The crab spiders themselves can change body colour between white and yellow, and their own body colour affects what substrate they choose to sit on (Heiling et al., 2005 b).

 


In a further chapter, we found that the fatal deceptive attraction for honeybees is found in UV-reflecting Australian crab spiders, but not in European crab spiders (Herberstein et al., 2009). It is not clear how UV reflection in Australian spiders evolved, whether it evolved once or several times independently.

 


 

References

Heiling, A.M., Herberstein, M.E., & Chittka, L. (2003). Crab spiders manipulate flower signals. Nature, 421, 334.

Heiling, A.M., Cheng, K., & Herberstein, M.E. (2004). Exploitation of floral signals by crab spiders (Thomisus spectabilis, Thomisidae). Behavioral Ecology, 15, 321-326.

Heiling, A.M., Cheng, K., Chittka, L., Goeth, A., & Herberstein, M.E. (2005a). The role of UV in crab spider signals: effects on perception by prey and predators. Journal of Experimental Biology, 208, 3925-3931. pdf

Heiling, A.M., Chittka, L., Cheng, K., &. Herberstein, M.E. (2005b). Colouration in crab spiders: substrate choice and prey attraction. Journal of Experimental Biology, 208, 1785-1792. pdf

Herberstein, M.E., Heiling, A., & Cheng, K. (2009).  Evidence for UV-based sensory exploitation in Australian but not European crab spiders.  Evolutionary Ecology, 23, 621-634.


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