Many spiders mimic other species – either as a defense against predators or as a way of predating on their model. The Amyciaea species belong to the crab spiders (Thomisidae family) and are 6-8 mm long.
Instead of looking like little crabs, like other Thomisidae, they are ant mimics and more specifically look like the Weaver Ant (Oecophylla smaragdina) on which they prey upon. Their colouration is the same orange as the Weaver Ants and they have black markings on the abdomen.
To tell the difference between the male and female the pedipalp size is indicative – bigger palps mean the spider is a male, because that is where he stores his sperm. The palps are the small appendages at the front of the spider near the mouthparts.
Their most interesting behavioral trick is the way they use their forelegs. These are most often in a jointed, raised position to mimic the antennae of the ants. They will also react defensively with the legs in that position, as you can see in the photos above.
I have seen them stalking the ants on a number of occasions. Weaver Ants are quite ferocious hunters themselves – I have observed them hunting down both other ant species and other bugs on the railings, and when hunting in a group they are formidable. Interestingly I have never observed them hunting the jumping spiders.
However the Amyciaea species are also very effective hunters and I have observed them hunting ants and in the process of the kill. I have seen them barging the ants, but I have not yet seen the final approach to subdue the ant.
I mainly see Amyciaea individually stalking ants on the railing, and often see a few around if there is a larger number of ants around. However, I once observed around eight Amyciaea attacking a large group of Weaver Ants that were going up onto the railing. The spiders were of varying sizes and sexes and were stalking the ants, or in the process of killing them. Ant bodies littered the railing. Every time I have seen the killing process the spider has attacked the ant on the top or back of the head, well away from the very strong pincer jaws that Weaver Ants have.
You can see in the photos how well they are able to attack an ant that is the same size or bigger than them. So if you see Weaver Ants moving on the railings watch out for the more erratic movements of the little Amyciaea hunting them!!