Macracantha arcuata


Macracantha arcuata is a species of orb-weaver spider in the genus Macracantha. Females possess a pair of extremely long, curved spines on the abdomen and are often brightly colored. M. arcuata occurs in forested areas from Northeast India and Bangladesh through Yunnan, Cambodia, Laos, Myanmar, Thailand, and Vietnam to Peninsular Malaysia, Singapore, and Borneo.

Description

Female long-horned orb-weavers have tough, shell-like abdomens armed with three pairs of spines. The spectacular middle spines project upward and outward, curving in toward each other along their length. They are up to three times as long as the abdomen is wide. The front and rear spines are short, relatively inconspicuous, and roughly equal in length.
The upper surface of the female abdomen ranges from yellow to red or even white or black and is marked with black sigilla. The ventral surface of the abdomen bears yellow or orange marks, and the median spines can show a bluish iridescence.
The male of the species measures only 1.5 mm, with stout, conical spines.

Ecology

Female M. arcuata build orb webs three or four feet wide in forested areas. These webs have hollow hubs and white silk beads on the radial threads. Siliwal and Molur report that females were more often observed on the underside of leaves near their webs than hanging in the center of the web.
In Singapore, the species depends heavily on primary rainforest.

Systematics

M. arcuata was historically included in the genus Gasteracantha. A 2019 study examining three mitochondrial and two nuclear genes found that M. arcuata is allied with Gasteracantha hasselti and Actinacantha globulata and that Gasteracantha is paraphyletic with respect to Macracantha, Actinacantha, and Thelacantha. The authors, however, did not propose generic reassignments based on their data.