Thursday, 19 September 2013

Getting the hang of camouflage

Yesterday, a late afternoon downpour cut short the foraging time for the blue-banded bees. The storm came from nowhere, as storms do at this time of year, dropped 20 mm of rain and then faded away almost as quickly as it had appeared. When the rain stopped, the bees came out of their shelters to gather what resources they could before the light faded.

But they weren't alone. As a blue-banded bee approached this cluster of flowers, two pairs of white legs emerged from between the petals. The legs were followed by eight beady eyes and a gleaming white body, wearing drops of rain as if they were the latest fashion accessories.

Crab spiders (Thomisus spectabilis) are ambush predators that rely on camouflage to hide them from their flower-visiting prey Most individuals are white, yellow or green and they choose their flowers according to their colours. From a distance the camouflage renders them invisible to bees, which are an important food item for the spiders. But when they get closer, the bees are able to detect the difference in contrast between the spider and its background. White spiders reflect ultraviolet light, which makes them stand out like spotlights against the UV-absorbing petals of white flowers.

What happens next depends on the type of bee. Introduced honeybees find the bright spot attractive, whereas native bees are inclined to land somewhere else.

But white on red — that doesn't work at all. This spider went to bed hungry.

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