Mastophora, also known as bolas spiders, is a genus of orb-weaver spiders first described by E. L. Holmberg in 1876. They can be identified by a pair of lumps on the dorsal surface of the opisthosoma, though not all males will have these lumps.

Adult females of the genus snare prey mid-air by using a silk line with an adhesive blob on the end, similar to bolas used by South American gauchos. They feed on flying insects, particularly moths, sometimes releasing pheromones that mimic those of their prey to attract them. Males and juvenile females capture their prey directly with their legs. Mastophora spiders have extreme sexual size dimorphism: adult females reach 0,75 inches (19 mm), while adult males are smaller than 0,067 inches (1,7 mm). These spiders reach maturity after two instars, or fewer. Cephalothorax often with dorsal protuberances, frequently paired. Female abdomen large, wider than long, an occasion has dorsal humps or lobes. Prey specialization by means of aggressive chemical mimicry. The attraction of preys by Mastophora is undoubtedly linked to an extraordinary endocrinoid abdominal tissue discovered histologically and named by A. Lopez, France (external link), a structure unfortunately ignored in english and spanish publications concerning the genus nevertheless America autochthonous.

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