The study of spider behavior reveals diverse strategies. These eight-legged arthropods employ sophisticated physical and cognitive adaptations to navigate their environments. Their behavioral repertoire ranges from unique methods of movement and migration to specialized hunting techniques and intricate communications. Understanding this diversity shows the varied lifestyles that have allowed spiders to colonize nearly every terrestrial ecosystem on the planet.
Locomotion and Non-Hunting Silk Applications
Spider movement relies on a combination of muscle power and internal fluid dynamics. Unlike most animals, spiders generally lack extensor muscles in the major joints of their legs; muscular contraction is only responsible for flexing the limbs inward. Outward extension is achieved through a hydraulic system, where pressure is generated in the cephalothorax, forcing hemolymph (blood) into the legs to push them straight. This fluid-powered mechanism allows for rapid, powerful movements, including the leaps performed by jumping spiders.
Silk acts as a tether and a vehicle for dispersal. As a safety line, the dragline is continuously deployed, anchoring the spider to a substrate and allowing it to safely drop from heights or bridge gaps. For migration, many smaller spiders, particularly spiderlings, use a technique called ballooning. The spider climbs to an elevated point, assumes a “tiptoe” stance, and releases fine strands of silk, or gossamer. These threads catch air currents, lifting the spider and carrying it away to a new location.
Diverse Hunting Tactics and Prey Capture
Most spiders are predatory, and their methods for securing a meal are varied. Orb-weavers construct geometrically precise webs, consisting of non-sticky radial threads for structural support and a sticky spiral thread for ensnaring flying insects. In vertical webs, the hub is often placed above the geometric center. This asymmetry allows the spider to run faster downward toward trapped prey due to gravity, optimizing the capture process.
In contrast, active hunters like wolf spiders (family Lycosidae) forgo webs entirely, relying on vision and speed to pursue and pounce on prey. They patrol the ground, using stalking and sprinting to subdue their victims. Another group utilizes ambush strategies, exemplified by trapdoor spiders. These spiders excavate silk-lined burrows covered by a camouflaged, hinged lid. They wait just inside, detecting the vibrations of passing prey before lunging out to capture their meal.
Crab spiders (family Thomisidae) are also ambush predators, but they employ camouflage, sitting motionless on flowers where their color often matches the petals to surprise visiting insects. Some specialists use deception, such as the bolas spider, which swings a silk thread tipped with a sticky globule. This globule releases a chemical that mimics the sex pheromones of female moths, luring male moths directly into the trap.
The Portia jumping spiders are arachnophagic, meaning they primarily hunt other spiders. These predators exhibit behaviors suggesting planning and problem-solving, such as taking long, circuitous routes that momentarily lose sight of the target to launch a surprise attack. When attacking web-building spiders, Portia may pluck the silk to mimic the vibrations of a struggling insect, luring the resident spider out of its retreat. Their ability to remember the location of prey for up to an hour, even when out of view, shows a level of intelligence rarely observed in invertebrates.
The Language of Vibrations and Courtship Rituals
Communication in the spider world is dominated by the sense of touch, relying heavily on substrate-borne vibrations. Spiders possess specialized sensory organs for this purpose. These include lyriform organs—clusters of slit-like structures embedded in the exoskeleton of the legs—which detect minute mechanical strains. Additionally, fine hairs called trichobothria sense air movements and vibrations, enhancing their sensitivity to the surrounding environment.
Vibrational sensitivity is central to courtship, which carries the risk of sexual cannibalism, where the female may mistake the male for prey. Male web-building spiders perform specific “shudder” or tapping sequences upon entering the female’s web. These patterned vibrations act as a species-specific password, signaling to the female that the visitor is a potential mate.
Many male spiders utilize strategies to mitigate this risk. Male wolf spiders perform displays involving leg-tapping and abdomen-quivering, producing seismic signals that indicate their quality as a mate. Other species, such as the nursery web spider, present the female with a silk-wrapped insect called a nuptial gift. This gift distracts the female and keeps her occupied with feeding, allowing the male a prolonged period for copulation. Some males exploit this system by wrapping worthless items, such as dried exoskeletons, in dense silk to extend the time it takes the female to discover the deception.
Parental Care and Survival Strategies of Spiderlings
Maternal investment in spiders is common in many species. The first act of care is the construction of the egg sac, a silk structure that protects the eggs from desiccation, temperature fluctuations, and predators. Females of many species, like crab spiders, guard this sac until the spiderlings emerge.
Extended maternal care is seen in active hunters like wolf spiders (family Lycosidae), which carry their egg sacs attached to their spinnerets, keeping the developing embryos mobile and protected. Once the young hatch, the female wolf spider tears the sac open to free her offspring. The spiderlings instinctively climb onto her abdomen, where they ride for several weeks while the mother continues to hunt and protect them.
Some social species have mothers killing prey and allowing their young to feed on it. The African social spider (Stegodyphus dumicola) exhibits matriphagy, where the mother allows her offspring to consume her body as their first substantial meal. This boosts the spiderlings’ survival and growth rates. Following this period of protection, young spiders must disperse to reduce competition and prevent sibling cannibalism. The primary mechanism for wide-ranging dispersal is ballooning, where the spiderlings release silk threads to catch the wind, carrying them across geographical areas.