Tailless Whip Scorpions

Tailless whip scorpions or whip spiders are arthropods belonging to the order Amblypygi, a part of the class Arachnida. The order’s name derives from the term ‘amblypygid,’ which means ‘blunt tail,’ referring to the lack of flagellum (tail) that is otherwise found in whip scorpions (Order Uropygi). Tailless whip scorpions are thus also referred to as amblypygids.

These arachnids are distributed in tropical and subtropical regions and usually inhabit under leaf litter, caves, and tree bark.

Description

Body Plan

The leg span of these highly flattened arachnids ranges between 5 to 16 centimeters (2.0 to 6.3 inches) and is divided into two segments: the unsegmented prosoma (cephalothorax) and the segmented opisthosoma (abdomen).

The first pair of legs, or chelicerae, are not used for walking but perform sensory functions. These sensory legs are slender and long, equipped with numerous sensory receptors, and stretch several times its body length.

Pedipalps

They have specialized raptorial pedipalps modified for seizing prey, just like the forelegs of mantises. These appendages are covered with spines and are kept folded in front of the cephalothorax when unused.

Pedipalp anatomy varies between species depending on their style of prey capture. For example, Euphrynicus has long, spineless pedipalps, while others have short, spiny ones.

Physiology

• Amblypygids have an open circulatory system, with the hemolymph flowing through sinuses and cavities rather than closed vessels.
• They respire through tracheal tubes that open to the exterior through spiracles on the body’s surface.
• The digestive system is relatively simple, where food gets broken in the mouth parts, followed by processing in the foregut and midgut.

Nervous System

Their nervous system consists of a brain located dorsally and nerve cords extending throughout the body.

Sense Organs

• A pair of median eyes are located at the front of the carapace above the chelicerae, which are usually large and more prominent than others. In contrast, two smaller clusters of three eyes are situated further back on each side of the carapace, with each cluster containing three eyes, making a total of six additional eyes on the sides.
• The first pair of legs are thin and long, with numerous sensory receptors helping them sense their surroundings.
• Sensory hairs and receptors are distributed throughout the body to detect environmental stimuli such as vibrations and chemicals.

Taxonomy

According to the World Amblypygi Catalog, the 265 known species of these arachnids have been divided into 5 families and 17 genera.

• Palaeoamblypygi
  • Paracharontidae (2 genera, 2 species, including Paracharon caecus, Jorottui ipuanai)
  • Weygoldtinidae (2 extinct species)
• Euamblypygi
  • Paracharonopsis (1 extinct species)
  • Charinidae (3 genera, 46 extant species, including Charinus ioanniticus, Sarax timorensis, Weygoldtia hainanensis)
  • Neoamblypygi
    • Charontidae (2 genera, 14 extant species, including Catageus longispina, Charon grayi)
    • Unidistitarsata
      • Kronocharon (1 extinct species)
      • Burmacharon (1 extinct species)
      • Phrynoidea
        • Phrynichidae (7 genera, 33 extant species, including Damon diadema, Phrynichus orientalis, Trichodamon princeps, Musicodamon atlanteus)
        • Phrynidae (5 genera, 1 extinct & 61 extant species, including Acanthophrynus coronatus, Heterophrynus longicornis, Paraphrynus mexicanus)
• Amblypygi incertae sedis (2 extinct genera, 2 extinct species)

Distribution

Tailless whip scorpions are primarily found in tropical and subtropical regions with warm and humid environments.

Habitat

These arthropods prefer dark and moist habitats, such as caves, leaf litter, under rocks, and tree crevices.

Diet

While arthropods comprise the bulk of their diet, amblypygids are also found to feed on some vertebrates, like frogs, lizards, or rodents, opportunistically.

Behavior

• Tailless whip scorpions are primarily nocturnal. They actively hunt for prey at night when temperatures are low and hide in dark crevices during daytime when temperatures are too high to venture out.
• Although they have eight legs, they use only six of them and walk sideways, just like crabs.
• Once a prey has been sensed using the antenniform legs, the victim is grabbed using the large spines on the pedipalps and immobilized immediately. The pincer-like chelicerae are then employed to grind the prey before ingesting it.
• Some species of amblypygids, including Phrynus marginemaculatus and Damon diadema, display social behavior, which is quite unusual among arachnids. Research from Cornell University suggests that mother amblypygids communicate with their offspring using their antenniform front legs, and the young reciprocate with their mother and siblings. This social behavior extends to defending their territories from other individuals.
• These arthropods are generally timid and lack venom, retreating to safer regions if attacked.

Lifespan

The average lifespan of these arachnids in the wild is 5 to 10 years, while in captivity, they can live up to 15 years.

Reproduction and Life Cycle

During mating, the male strokes the female with his whip-like front legs and deposits stalked spermatophores, which contain one or more sperm masses at the tip, onto the ground. He then uses his pedipalps to guide the female over these spermatophores. The female gathers the sperm from the spermatophores and fertilizes her eggs internally in a sac carried under the abdomen. After hatching, the young climb onto their mothers’ backs, while those that fall off before completing their first molt die prematurely. The young are usually carried for about 4 to 6 days.

Like all arachnids, tailless whip scorpions molt multiple times during their lifetime. They usually shed their exoskeleton using gravity by hanging from the underside of horizontal surfaces.

Predators

Tailless whip scorpions are preyed upon by frogs, lizards, birds, rodents, and larger arthropods, like spiders, predatory beetles, and mantises.

Adaptations

• The front pair of legs (‘antenniform’) is modified into segmented antennae-like feelers giving them the ‘whip-like’ look for sensing their immediate environment.

Interesting Facts

1. Tailless whip scorpions may go without food for a month because they usually do not eat before, during, or after molting.
2. Phrynus longipes was the first amblypygid ever found feeding on a bird, an Antillean crested hummingbird in the British Virgin Islands.