The magnificent, not to mention distinctive, Long-Horned Orb Weaver easily impresses those fortunate enough to view it. The invertebrate does not, however do so due to sheer physical size. That’s because it’s actually quite tiny, especially compared to some others. Much like many arachnids, though, it also displays the physiological characteristic of sexual dimorphism. In its specific case, this trait manifests itself in terms of pure physical size.
That trait further results in a rather extreme difference in the sizes of the genders. Among the females, body lengths average 0.8 – 1.0 in (2.0 – 2.6 cm). This measurement, however, narrows to about 0.31 – 0.35 in (0.8 – 0.9 cm) at the waist. The males, meanwhile, only reach a fraction of this size. They measure about (0.15 cm) at the waist. The body also displays different color patterns between the upper and lower surfaces.
The upper surface of the body ranges in color from red, to yellow, to white, or even black. It also displays black spots. The underside of the body, though, shows yellow or orange. Yet the amazing Long-Horned Orb Weaver stands out for one more reason. That’s the long horn-like structures, displayed only by the females. That’s yet another form of gender-based difference it manifests. These reach many times the length of the body of the arachnid
Why would female Macracantha arcuata, a species of Long-horned orb weaver spiders found in India and China through Southeast Asia to Borneo, have such long, curved spines on their abdomens?
“One of the functions of this orb-weaver spider’s unusual giant stiff horns protuding from its back is probably so that predators (such as birds and lizards) will have a very hard time trying to swallow it.
“The females have very long curved spines on the abdomens which are more than 3 times (24-27mm) its body size which is (8-9mm).”
Via Wikipedia, males are much smaller: “1.5 mm, with stout, conical spines.”
The last part of the video appears to show the female spider in ultraviolet or blacklight.