If it weren’t for the fact that these arachnids are utterly harmless and slightly more obscure than the mygalomorphs and scorpions, they would certainly occupy a distinguished position in the vanguard of nightmares’ creatures. However, to label them as a simple curiosity or a Halloween special does them a disservice. They form an ancient, and successful sister-clade (branch with most recent common ancestor) to the vinegaroons (Uropygi) and schizomida (microwhip scorpions). Their adaptations (dorso-ventral flattening of the body, spinose raptorial pedipalps and modification of forelegs into exquisitely sensitive sense organs) have led to successful speciation (155 species in 5 different families) and radiation across the tropics.
Like most creatures occupying the realm of nightmares, she emerges when sun yields to night, and our imaginations conquer good sense. She may materialize from a cavern or cave, a burrow or some long-abandoned retreat. She advances tentatively into the open, her sedate pace belying her incredible agility and speed. Her obscenely long forelegs swing to and fro, scanning, probing the ground ahead of her for potential prey, mates or rivals. These highly modified legs appear as long, fragile extensions (or ‘whips’) but they are instrumental in forming an image of her environment since the small clusters of ocelli on her prosoma (cephalothorax) are oriented upwards and serve little purpose in the highly detailed and colour-based sight as we know it (rather they are thought to function in the regulation of circadian rhythms by discerning light/dark cycles, as well as the perception of vague movements, and overhead obstacles (important in determining the exposure of her daytime retreat). The antenniform legs also play a key role in hunting; packed with a dense diversity of afferent (sensory) receptors in the form of (at least) 7 different types of sensillae.
These receptors range from the mechanosensory slit sensillae (important in the perception of mechanical deformation and/or strain), trichobothria (measuring pressure differentials), joint receptor(s) (proprioceptor(s) which sense stimuli arising within the joint regarding position, motion, and equilibrium) to chemosensory (mostly olfactory) sensillae. While the bulk of the sensory information appears to come from the antenniform legs, and indeed these play a crucial role as outlined above, other mechano/chemosensory organs have been found on the claws and pedipalps, perhaps ensuring a level of redundancy in case the fragile forelegs are damaged, severed or lost by autotomy (a survival strategy whereby a limb is sacrificially amputated (a pre-severed limb is held together along fracture planes (1), and it is the controlled failure of adhesion mechanisms through internal and external forces which allow the limb’s release) to assure the safety of the organism as a whole). The combination of these sense organs help Amblypygi develop and maintain a multi-dimensional awareness of their environment, while mushroom bodies and neuropils (areas of dense synaptic connectivity) found within the brain have been associated with more complex behaviours such as learning and memory and the more recently hypothesized integration of diverse and complex stimuli (2), (3). Essential to the relay of all this information are giant peripheral interneurons occupying the antenniform legs, and though the full extent of their role has yet to be determined, it has been posited that the increased diameter of the axonal fibres and hence faster conduction speeds are important in the large distances that a signal must travel within these elongated limbs, which would otherwise suffer from signal degradation and lengthier stimulus-response times.
While in situ studies of predatory behaviour are few and far between, there are several laboratory studies which demonstrate a 4 stage hunting strategy: 1) Prey is first encountered and assessed. The antenniform legs are alerted to the presence of prey by airborne or ground vibrations enabling the reorientation, aiming and tracking of the prey while the body as a whole remains stationary. Mechanosensory sensillae determine the prey’s distance and relative position, while olfactory organs determine the prey type. Unfortunately there is insufficient data to determine whether Amblypygi adapt their hunting strategies to specific prey size and type; however, given the sheer number and diverse types of sensillae it stands to reason that there is probably a certain degree of prey discrimination 2) Next, the antenniform legs will gently contact either side of the prey (surprisingly without initiating the prey’s flight response). This is thought to either guide the prey into a more vulnerable position, or else to provide additional information 3) The whip spider then unfolds its pedipalps revealing raptorial spines and frames the prey with its antenniform legs without actually touching it, composing a strike ‘image’ to accurately judge distance, speed, etc. 4) Finally the sensory legs are swept aside as the prey is impaled on the spines of the open pedipalps.
Observations of mating amblypygi are rare in the wild, and photos even more so; however several documented accounts relate a scenario similar to the more familiar scorpion and Uropygi mating rituals. Notably, a short courtship involving a touching and stroking of the forelegs, a pedipalp embrace, the deposition of a spermatophore directly onto the substrate and the guidance of the female by the male over the sperm packet upon which she lowers herself. Eggs develop in a case held below the opisthosoma (abdomen) and hatch approximately 3-4 months later.
Like some other basal lineages (Thelyphonida and Scorpions), mothers exhibit a degree of subsocial behaviour (ie. care for their young). This is most obvious in the manner in which they carry their newly hatched young (first instar stage) on their backs until their first moult (second instar stage) when their antenniform legs become sufficiently developed to allow them to hunt for themselves. This seemingly trivial extension of maternal care offers substantial evolutionary advantage in neonatal survivorship at a time when mortality rates are at their highest. Furthermore some species have been demonstrated to show kin recognition in successive moults with concomitant decreases in aggression (4).
Photographs of this group typically rely on frontal portraits of the head and pedipalps. This highlights two key features: 1) The eyes; though functionally of little value these are still important compositionally, and 2) The spines which ornament most/all amblypygi pedipalps. This is an effective view and probably offers the most advantageous perspective which includes the most features.
Other views to consider might be overhead closeups of the head (first image of this section and below).
Or else high magnification views detailing armature and spines (below). Owing to their nocturnal nature, properly photographing amblypygi within their environment through wide-angle macro can be difficult, though provided there are interesting topographical features this may be a desirable perspective. Nb. that this will require either a multi-flash setup or a single flash fired multiple times with a longer shutter speed.
Alternatively, many amblypygi show beautiful translucence with delicate whites, purples and blues immediately following ecdysis (moulting). Unfortunately this highly photogenic phase is quite short-lived, usually no more than 30 minutes. Therefore if ecdysis is imminent it is probably best to remain nearby and check in frequently. During this teneral stage they also display a small amount of UV reflectance which disappears completely as the exoskeleton hardens and becomes increasingly pigmented.
A clip from “Life in the Undergrowth” narrated by David Attenborough: