Cobweb spiders (family Theridiidae) are common arachnids often found in human dwellings globally. This diverse group includes species like the common house spider and the black widow spiders. Cobweb spiders construct a three-dimensional, chaotic-looking web known as a tangle web or cobweb, rather than an orb-web. This unique architecture is a passive, effective tool for capturing a wide variety of prey. Their hunting strategy relies on the mechanical failure of specialized silk lines, followed by a rapid attack sequence.
The Architecture of the Tangle Web
The haphazard appearance of a cobweb hides a specialized, three-dimensional hunting structure designed to capture both flying and ground-dwelling prey. The web has two main functional components: the aerial tangle and the gumfoot threads. The upper, crisscrossing threads form a non-sticky scaffolding that entangles flying insects that blunder into the silk mass. This aerial section provides the spider with a protected retreat and a stable anchor point.
The gumfoot apparatus is the innovative component, consisting of vertical, sticky threads anchored to the substrate below. The spider coats the lowest section of these threads with viscid silk that adheres weakly to the ground using specialized attachment discs. Held under tension, these gumfoot threads function as spring-loaded trip lines for crawling insects. When a ground-dwelling arthropod disturbs the line, the weak attachment disc snaps free, pulling the prey upward and suspending it in the sticky silk.
This design maximizes the range of prey the spider can capture. The gumfoot discs trigger a mechanical release when disturbed, contrasting with the strong adhesion of the scaffolding discs used to anchor the main structure. This architectural division allows the web to efficiently ensnare airborne and terrestrial targets.
Primary Prey and Nutritional Sources
Cobweb spiders are generalist predators, consuming a broad spectrum of arthropods intercepted by their webs. Their diet consists primarily of insects and small arthropods, making them natural pest controllers. The non-sticky, upper tangle portion of the web catches common flying pests. These include flies, mosquitoes, and small moths.
The sticky gumfoot threads expand their menu to include ground-crawling prey that evade other web types. This mechanism makes them predators of ants, beetles, woodlice, and hard-bodied insects like cockroaches. Subduing robust prey depends on the spider’s size and the trip-line mechanism’s effectiveness in suspending the victim.
Cobweb spiders attempt to tackle prey significantly larger than themselves if the web can hold the struggling creature. They also engage in opportunistic feeding, sometimes consuming other spiders or stealing prey from other webs (kleptoparasitism). The diversity of their food sources highlights their adaptability as effective ambush hunters.
The Dynamics of Capture and Feeding
The hunting process starts when prey strikes the web, generating vibrations detected by specialized sensory organs on the spider’s legs. The spider assesses the prey’s size and struggle by interpreting these vibrations before approaching. Instead of biting immediately, the cobweb spider uses a capture technique that involves silk wrapping.
The spider rapidly approaches the prey and uses its comb-like hind legs, called the tarsal comb, to fling specialized silk threads onto the victim. This process, known as silk wrapping or swathing, quickly immobilizes the prey before direct contact is made. The wrapping silk is optimized for toughness to withstand the struggling insect’s energy output.
Once securely bound, the spider delivers a venomous bite using its chelicerae, injecting neurotoxins or digestive enzymes. Spiders rely on external digestion because they cannot chew solid food. The venom contains powerful enzymes that liquefy the prey’s internal tissues into a digestible broth. The spider then ingests this liquid slurry using its sucking stomach, leaving behind the desiccated husk.