page_title: Progradungula otwayensis
section_title: Behavior
hierarchical_section_title: Progradungula otwayensis / Behavior
caption_attribution_description: English: Progradungula otwayensis - Catching ladder in front of a hollow in a large tree fern
context_page_description: Progradungula otwayensis, commonly known as the odd-clawed spider, is a species of cribellate spider endemic to the Great Otway National Park of Victoria, Australia. It is one of only two species in the gradungulid genus Progradungula.
  Odd-clawed spiders are medium-sized to large spiders, with an approximate body length of 10 to 15 mm and a leg span of 72 to 77 mm. They are lightly pigmented, from yellowish brown to light mauvish gray, with three chevron markings on the rear upper part of their abdomen. Like other gradungulids, their legs are tipped with three claws. These claws are particularly well-developed on the first and second leg pairs and are used for latching unto prey. They are ambush predators, building characteristic ladder-shaped snares close to the ground. They stand head-down on these webs waiting for prey which they then scoop up into these webs to trap them.
context_section_description: Odd-clawed spiders are nocturnal. During the day, they rest inside their retreats in the tree hollows. An hour or so after sunset, they emerge to build their webs or to hunt.
  Along with Progradungula carraiensis and Macrogradungula moonya, odd-clawed spiders are one of the only three species belonging to the family Gradungulidae that are cribellate. Unlike other members of the family which are all cursorial (active roving hunters), these three species are ambush predators that construct snares. The snares are made from silk spun from specialized spinnerets known as the cribellum, and combed with the row of bristles (the calamistrum) on their fourth leg pair. Unlike normal spinnerets, the cribellum produces extremely fine silk that can easily entangle prey without the need for glue. The snares of all three species are distinctively ladder-shaped, in contrast to the snares of other cribellate spiders from other families.
  The larger part of the odd-clawed spider's web is composed of a network of supporting threads built up to 2 m (6.6 ft) above the ground. Two lateral support threads extend from this network and are attached to vegetation or ground below. These threads are held more or less parallel to each other by several short bridge threads. The spider spins the catching ladder in between them, composed of a loose irregular zigzag of cribellate thread. The catching ladder and the supporting webs are usually built far from the retreat of the spider in the tree hollows, as far as 3 m (9.8 ft) away. The retreat and the webs are connected to each other by a single sturdy thread.
  The prey-catching behavior of odd-clawed spiders is similar to that of Progradungula carraiensis and Macrogradungula moonya. The spider takes position on its catching ladder with its head facing downwards toward the substrate. In this position, its fangs are at about the same level as the lowest "rung" of the catching ladder. The third and fourth pair of legs are used to stretch and hold the catching ladder behind the spider. The first and second pair of legs are held outstretched in front of the spider, just above the ground level. The second pair of legs may touch, or at least is very close to, the lateral support threads. Through these threads, the spider senses vibrations coming from the ground. These vibrations (in addition to air currents) warn the spider of approaching prey.
  When a prey animal is detected within the range of the spider, it lunges with its clawed front legs and scoops it up into the catching ladder, also administering a bite in the process. The catching ladder detaches from the lateral support threads and entangles the prey. Due to its elasticity, the cribellate threads can stretch to comfortably envelop even large prey. The spider restrains the enmeshed prey while continuing to inject it with venom. When the prey stops moving, the spider relaxes its hold, turns around on the web and begins wrapping the prey in silk. The catching ladder is destroyed during the capture and the spider may rebuild it during or even before feeding on the caught prey.
  Odd-clawed spiders also have similar defensive behavior as Progradungula carraiensis. During low-level disturbances, they retreat towards the upper support webs or dismount towards the nearest surface. In greater threat levels, however, they immediately drop from their webs to the ground and "play dead" (thanatosis), assuming an inert posture with their legs tightly held against their bodies.
  In contrast to adults and immature individuals, all the juveniles were observed to build their catching ladders and support webs inside the tree hollows. No catching ladders of juveniles have been found in the open. This seems to indicate that early instars of odd-clawed spiders live exclusively within the tree hollows.
caption: Catching ladder of P. otwayensis in the hollow of a large tree fern
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