Phrynidae Blanchard 1852

Phrynidae is a mostly Neotropical family of medium-large amblypygids, (Quintero, 1981). Amblypigids, also known as whip spiders or tailess whip scorpions, are a little-studied order of arachnids that are notable for their modified whiplike forelimbs and formidable spined pedipalps (Hebets, 2002), which they use to capture arthropods and some times small vertebrates (Owen & Cokendolpher, 2006). Many whip spiders live in caves, and those above ground are strictly nocturnal (Quintero, 1981). While formidable in appearance, whip spiders are not toxic and are harmless to humans (Santer & Hebets, 2009).

Phrynidae consists of 4 extant genera: Phrynus, Paraphrynus, Acanthophrynus, and Heterophrynus (Quintero, 1981). Phrynids, due to their abundance throughout the Neotropics, are some of the better-studied members of Amblypygi, with much of what little we do know about whip spiders’ life history coming from these organisms (Hebets, 2002).

Phrynidae is a primarily Neotropical family, ranging from southern Florida and the Caribbean to the Amazon Basin (Quintero, 1981). Phrynus, Paraphrynus, and Acanthophrynus are mostly represented by Mesoamerican species, whereas Heterophrynus contains typically South American species. One species of phrynid, Phrynus exsul, is solely known from the Flores and Rinca islands of Indonesia, making it the only known Paleotropical member of its family. (Harvey, 2002)

Phrynids are medium-large amblypygids, with the largest individuals reaching up to 45mm in body length. (Quintero, 1981) Like other amblypgids, they possess a dorsoventrally flattened body (Hebets, 2002) with a wide prosoma (the anterior of the two body segments in some chelicerates, also called the cephalothorax) that gives them a distinctly mushroom-shaped appearance. This body plan is usually associated with heightened olfaction in arthropods (Hebets & Chapman, 2000, A). The foremost legs of amblypygids are transformed into antenniform structures often known as “whips” (Fowler-Finn & Hebets, 2006) that contain up to 10 different sensory organs for detecting a variety of chemical and mechanical stimuli (Hebets, 2002). Because of their radically altered forelegs, amblypygids walk on only 3 pairs of legs, like insects (Fowler-Finn & Hebets, 2006).Hairs sensitive to air movements called trichobothria are found on the walking legs of amblypygids, and are another important sensory organ (Santer & Hebets, 2009).

Large spined pedipalps used in prey capture and intraspecific interactions are another shared feature of all amblypygids, with specific morphology of the weapons varying from species to species (Hebets, 2002). Some species of phrynids display sexual dimorphism in their pedipalps, with those of the males growing longer in proportion to their bodies than in females (Quintero, 1981; Weygoldt et al., 2010).

Phrynids are morphologically distinguished from other amblypygids by having 4 tibial segments on leg IV (except for Phrynus daimonoidaensis, which only has 3) and lacking pulvilli (adhesive pads on the tarsi of many arthropods) of their walking legs (Quintero, 1981).

Unlike most arachnids, amblypygids have a well-developed olfactory system between the anatomy of their whips and the arrangement of their nervous system (Hebets, 2002). Studies have shown they can detect and respond to a wide variety of volatile chemicals found in their environment, similar in range to many insects (Hebets & Chapman, 2000, A). While amblypygids possess 8 eyes on their prosoma, they lack a tapetum, the light-reflecting layer used for night vision in some spiders. This makes their eyes virtually useless in their nearly pitch-black natural habitats, so they mostly rely on olfaction and mechanoreception (Hebets, 2002). Amblypygids usually walk sideways, like crabs, waving their antenniform legs in front of them as they go. (Levi et al., 1968).

Male phrynids have been observed wandering more than their relatively sedentary female counterparts, likely searching for mates. This observation likely applies to all amblypygid families (Fowler-Finn & Hebets, 2006).

Amblypygids may fight same-sex members of their species to decide competitions over resources, territories, and possibly mates. In phrynids, a study on agonistic interactions (on Phrynus marginemaculatus) showed that male-male contests consists primarily of rapid flicking of the whips combined with pedipalp displays. If a victor isn’t decided from such displays, these “battles” can sometimes escalate into the combatants contacting each other’s pedipalps and elevating their bodies off the ground, using their open pedipalps to push away from each other. Whichever individual remains elevated the longest typically wins, with the loser retreating uninjured. Females will fight each other similarly, but fight more shorter periods and are more likely to escalate to the contact phase. This may be because wandering males are more likely to come into contact with each other than females, leading to the sexually dimorphic evolution of a more ritualized fighting behavior. Because both males and females exhibit this behavior, it is likely that the battles are not primarily over mate choice. (Fowler Finn & Hebets, 2006)

At least some phrynids have the ability to survive for extended periods underwater, a useful adaptation for small animals in flood-prone areas. A study on Phrynus marginemaculatus showed that when submerged, the amblypygid could perform plastron respiration to take in enough oxygen from the surrounding water to survive without negative consequences for over 24 hours. Plastron respiration is the ability of some arthropods to maintain a bubble of air around their cuticle using surface tension. Ambient oxygen can diffuse through the bubble, allowing the arthropod to survive underwater. Phrynus marginemaculatus is the first known animal without a tracheal respiratory system (like most arachnids, amblypygids possess book lungs) to perform plastron respiration. (Hebets & Chapman, 2000, B)

Observations at Barro Colorado Island in Panama have shown that Phrynus gervaisii individuals are found more commonly than expected by chance in front of active colonies of Paroponera clavata, the bullet ant. The whip spiders are ignored by the predatory ants, even when they go into a craze defending their nest, and the whip spiders in turn make way for the ants as they enter and leave the nest. This suggests that at least some phrynids have developed an inquiline relationship with the bullet ant, wherein setting its territory near an ant colony protects the whip spider from diurnal predation (how this might serve the ants is unknown) (LeClere et al., 1987).

Breeding in at least some phrynid species appears to be concentrated in the dry season, although low levels of breeding occurr year-round (Hebets, 2002).

Amblypygid courtship consists of the male orienting himself towards the female and vibrating his whips for several minutes, as in same-sex agonistic interactions. The male then deposits his spermatophore, a sperm-filled capsule attached to the substrate by a flexible stalk, and steps backwards to lure the female into taking up his sperm. (Weygolt et al., 2010)

Phrynids are distiguished from other amblypygids in the scultped, triangular heads of their spermatophores (Peretti, 2002), and a unique step in courtship where the male embraces his spermatophore for some minutes with his pedipalps before luring the female to it; the purpose of this is unknown (Weygolt et al., 2010).

All amblypygid females carry their eggs in a sac on the ventral side of their opisthosoma (the posterior segment of the chelicerate body). In phrynids, the eggs tend to develop for around 4 months (Weygolt et al., 2010). The hatched nymphs are then carried on the mother’s back for about 2 weeks (Weygolt et al., 2010), longer than average amblypygid period of 4-6 days (Levi et al., 1968).

Little data exist on predation of amblypygids, but one individual was observed being eaten by a scorpion (Scorpiones) (Fowler-Finn & Hebets, 2006).

A possible inquiline relationship between Phrynus gervaisii and the giant Neotropical ant species Paroponera clavata has been observed on Barro Colorado Island (LeCLere et al., 1987), and could extend to other species of phrynids across the bullet ant’s range. See “Behavior” section for details.

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Phrynidae is a family of amblypygid arachnida arthropods also known as whip spiders and tailless whip scorpions. Phrynidae species are found in tropical and subtropical regions in North and South America. Some species are subterranean; all are nocturnal. At least some species of Phrynidae hold territories that they defend from other individuals.