Mastophora Holmberg, 1876

Rather than constructing an orb web like many of its close relatives, adult female Mastophora bolas spiders construct a "bolas" (named after a traditional South American throwing weapon)-- a sticky globule at the end of a silk thread --and hold it with a foreleg. This behavior was first reported by C.E. Hutchinson in 1903, based on observations in southern California (Yeargan 1994). Spiders hunt with a bolas only at night. The female releases an allomonal blend that mimics the chemical signals used in long-range mate attraction by her moth prey (an allomone is a chemical produced by an organism which induces in a member of another species a behavioral or physiological reaction favorable to the emitter). Because female moths are the mimicked signalers in this system, only male moths (duped responders) are subject to predation by the spider. Based on their studies of Mastophora hutchinsoni in Kentucky, Haynes et al. (2001) suggest that there is a dynamic interplay between olfactory cues (pheromone mimics) emitted by the bolas spider and mechanosensory cues (wing vibrations) from the moth, which are detected by the spider. The bolas spider aggressively mimics the pheromone blend of its moth prey. Spiders frequently emit this chemical cue even before they have produced the weapon (bolas) that would allow them to capture a moth. The allomone attracts prey moths that are downwind of the spider. The wing vibrations of an approaching moth stimulate the spider to produce a bolas. Subsequently, wing vibrations also stimulate the strike that allows the spider to capture its prey. (Haynes et al. 2001).

Eberhard (1977, 1980) studying a previously undescribed species of Mastophora in Colombia, was the first to confirm the suspicion of the early naturalists that Mastophora lures its prey with a volatile substance that mimics the sex attractant pheromone of virgin female moths. In formally describing this species (Eberhard 1980), he named it Mastophora dizzydeanii, explaining: "Since this spider’s livelihood depends on throwing a ball fast and accurately, it seems appropriate to name it in honor of one of the greatest baseball pitchers of all time, Jerome "Dizzy" Dean."

Bolas spiders, a group including five recognized genera, are known from most parts of the world outside temperate Eurasia, but about half of the known species of Mastophora occur in South America (Yeargan 1994 and references therein).

In temperate regions, the tiny male Mastophora become adults about 2 months before females mature. Late-instar and adult females attract certain male moths by aggressive chemical mimicry of those moth species' sex pheromones. While hunting, these larger female spiders hang from a horizontal silken line and capture moths by swinging a ``bolas'' (i.e., a sticky globule suspended on a thread) at the approaching moths. In contrast, small, early-instar bolas spiders of both sexes attract flies in the genus Psychoda, which they capture without using a bolas or web. Instead, they position themselves along leaf margins and use their front two pairs of legs to grab approaching prey. Field experiments have demonstrated that adult males of the bolas spider Mastophora phrynosoma attract adult male Psychoda phalaenoides. Each year during a 3-year study, significantly more P. phalaenoides were captured on sticky traps baited with live adult male M. phrynosoma than on unbaited control traps. Thus, the tiny adult male bolas spiders retain the juvenile hunting tactic of attracting psychodid flies, while female bolas spiders switch from hunting psychodid fles as spiderlings to hunting moths when the female spiders become older and larger. Mastophora dizzydeani and M. hutchinsoni have also been reported to hunt without using a bolas for several weeks after spiderlings emerge. (Yeargan and Quate 1996, 1997 and references therein)

As a moth approaches a hunting adult female Mastophora bolas spider, the spider first draws back the bolas and then rapidly flicks it in the direction of the moth. These behaviors are likely stimulated by detection of the moth’s wing beat, because the spider can be induced to draw back the foreleg holding the bolas with low-pitched humming (Eberhard, 1980; Haynes et al. 2001 and references therein). The sticky globule penetrates through the moth’s scales to the underlying cuticle. Subsequently, the spider bites and paralyzes the moth before she wraps him with silk. (Haynes et al. 2001 and references therein)

Yeargan (1994) summarizes the hunting behavior of Mastophora, Cladomelea, and Ordgarius bolas spiders. The manner in which the bolas is swung differs among groups from the three major regions of distribution. In the Americas, Mastophora species hold the bolas essentially stationary with a front leg until a moth approaches, at which time the spider cocks the leg and swings the bolas toward the prey with a very rapid, pendulum-like stroke. In contrast, Ordgarius species in Australia begin to rapidly whirl the bolas when they detect an approaching moth. The African C. akermani apparently does not wait for a moth to approach, but instead whirls the bolas immediately after it is prepared and does so continuously for about 15 minutes, Mastophora frequently miss their targets, and the same bolas can be swung at prey repeatedly. When a moth is struck, it rarely escapes, despite its struggles. It adheres to the sticky globule and hangs twirling on the vertical line. The spider descends to the moth, or sometimes draws the prey up by the line, and bites it. After waiting several seconds the spider wraps the prey, mummy-like, in silk. The wrapped prey may be fed upon immediately, but often the spider will attach it to the horizontal line and prepare a new bolas. Several moths may be caught and stored before the spider ceases hunting and begins to feed, Two studies indicate that adult female Mastophora catch an average of about two moths per hunting night, but occasionally an individual catches as many as six or seven moths during a single night. At least occasionally, in at least four Mastophora species, a spider has been observed making a longer than normal horizontal line and, rather than preparing a single bolas, hanging several on the line (as many as nine have been observed). These spider have then positioned themselves at one end of the horizontal line but did not hold a bolas; no prey capture has been observed using this method. (Yeargan 1994 and references therein)