Posts Tagged ‘mimicry’
The amazing Green Tree Ant-mimicking crab spider (Amyciaea albomaculata) relies on subterfuge to deceive its’ prey. Green Tree Ants (Oecophylla smaragdina) are an abundant food source, but getting close enough to bag and eat them requires evolutionary assistance. The spider’s abdomen has two black dots resembling eyes and it presents the abdomen as a head to fool the ants. We suspect that there’s a little more to it, than just the colour. We know that a Green Tree Ant nest brought in from a different colony, will be demolished in a short time, yet their inhabitants are green ants. So what’s the difference?
Over the past couple of weeks I have been seeing a curious-looking spider hanging horizontally and upside-down, paralleling a branch and suspended along a single line of silk. This posture is exclusively nocturnal and suggests the spider is hoping to attract insects that rest upon silken threads. With legs flexed , the overfall appearance (under torchlight) was like a piece of exfoliated lichen.
This marvellous Twig-mimicking Orb-weaver (Poltys noblei) convinces the world, but especially birds, that it is a twig. In the image (above) the spider’s eye-stalk protrudes downwards between its medial four legs at the bottom, whilst the four hind legs bunch up in bi-lateral compartments that parallel the proximal end of the superior face of its abdomen. Silk blends the spider’s colour along the end of the ‘real’ twig, to help the spider camouflage itself, and in an extended continuation of the branch, remains motionless all day to protect itself from the keen eyes of hungry birds.
The Fruit Piercing Moth (Eudocima aurantia) is another master-of-disguise. In case it isn’t obvious, the up-turned elongate ‘horn’ (right) mimics the petiole of a dead leaf, complementing the greater character of the moth’s design for the same purpose – to convince the world that it is a dead leaf. Replete with venation and even the speckled adornments of mould-colouring, the design is very convincing.
In the Daintree Rainforest, blending into the landscape is core business for anything that is potentially bird-food. At a glance, the branch in the image (above) is unremarkable. Zooming in a little closer reveals a population of phasmids, successfully hidden from the vigilance of a multitude of avian dangers. How many can be seen?