Bolas Spiders - Systematics

Systematics

Bolas spiders are species of three related genera:

• Mastophora (American Bolas, 48 species)
• Cladomelea (African Bolas, 4 species)
• Ordgarius (Australasian Bolas, 12 species)

Traditional orb webs are not effective for capturing moths, because only their scales will stick, allowing the moth to escape. The ladder webs of Scoloderus species appear to be adaptations in web design to increase moth capture. These webs extend vertically about seven times their width. When a moth slides down the web, it leaves a trail of scales until its body sticks to the web. However, these spiders do not seem to be closely related to bolas spiders. The nearest relatives seems to be the Cyrtarachneae (e.g. Pasilobus) of the Paleotropics. They also specialize on moths, and use threads that are beaded with sticky droplets. Celaenia and Taczanowskia species in South America seem to use chemical attractants to catch moths, too, and may also be closely related to bolas spiders.

At least four Mastiphora species are known to sometimes, instead of preparing a single bola, to hang up to nine droplets on one horizontal line. This has not been observed to result in prey capture, but is remarkably similar to the midline of a Pasilobus web in which the low-shear joints of spanning threads have been broken.

Interestingly, the not closely related araneid genus Kaira uses a pheromone very similar to Mastiphora to catch moths, however it does not use a bola, but instead catches the insects with a basket formed from its legs.