terminal web assembly

Definition

Target type: biologicalprocess

The aggregation, arrangement and bonding together of a set of components to form a terminal web. [GO_REF:0000079, GOC:kmv, GOC:TermGenie, PMID:21949650]

Terminal web assembly is a complex biological process primarily observed in certain species of spiders, particularly in the family Araneidae (orb-weaver spiders). It involves the construction of a specialized silk structure called a "terminal web," which serves as a crucial component of the spider's prey capture strategy. Here's a detailed breakdown of the process:

1. **Silk Production:** The spider begins by producing several types of silk from specialized glands called spinnerets located at the posterior end of its abdomen. The specific types of silk used in terminal web assembly include dragline silk (strong and sticky) and viscid silk (extremely sticky).

2. **Web Construction:** The spider starts by constructing a traditional orb web, a circular structure with radial threads and a spiral of sticky capture threads. The terminal web is then built as an extension of the orb web, often positioned at the bottom or a specific edge of the orb web.

3. **Terminal Web Structure:** The terminal web consists of several layers of silk, usually including:
* **Dragline Threads:** These form the basic framework of the terminal web, providing strength and support.
* **Viscid Threads:** These are the sticky threads that trap insects. They are often arranged in a dense, complex pattern to maximize the chances of entrapment.
* **Signal Threads:** Some terminal webs also incorporate thin, sensitive signal threads that vibrate when an insect gets caught, alerting the spider.

4. **Prey Capture:** The terminal web acts as a secondary capture mechanism, particularly for insects that are too large or strong to be effectively caught in the orb web alone. Insects flying into the terminal web get stuck in the sticky threads. The spider, sensing the vibrations through the signal threads, quickly rushes to the terminal web and immobilizes the trapped prey.

5. **Advantages of Terminal Webs:**
* **Enhanced Capture Efficiency:** The terminal web extends the area of the spider's hunting zone, increasing the chances of catching prey.
* **Specialized Prey Capture:** Terminal webs are particularly effective for capturing larger or heavier insects that might escape the orb web.
* **Improved Stability:** The terminal web can add additional stability to the orb web, especially in windy conditions.

6. **Evolutionary Significance:** The evolution of terminal webs is thought to be a successful adaptation that allows certain spiders to exploit a wider range of prey resources. This strategy has been particularly successful in species that occupy environments where large or strong insects are common prey.

7. **Variations:** The exact structure and arrangement of terminal webs can vary significantly between spider species. Some spiders may have elaborate terminal webs with multiple layers of silk and complex patterns, while others have simpler structures. The specific design is often influenced by the size and hunting behavior of the spider.

8. **Beyond Capture:** In some species, the terminal web may also serve as a shelter or a retreat for the spider when it is not actively hunting.'
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