Many people wonder if the spiders they encounter in their homes possess the ability to jump. This common question often arises from observing their quick, sometimes startling, movements. Understanding the typical locomotion of house spiders and differentiating it from the specialized jumping of other spider species can clarify these observations.
House Spider Movement
Most common house spiders do not jump. These arachnids primarily rely on rapid running or scuttling to navigate their environment. For instance, giant house spiders (Eratigena atrica) are known for their speed, running up to half a meter per second. Their leg structure and musculature are adapted for swift, horizontal movements, not for launching into the air.
House spiders also frequently use silk for movement, particularly for controlled descents. They can drop from elevated positions using a dragline of silk, which acts as a safety tether. This allows them to quickly move downwards or escape perceived threats without leaping. Their anatomy supports this controlled falling and quick scuttling, distinct from a propulsive jump.
Mistaken for Jumping
The perception that house spiders jump often stems from their sudden, darting actions. When a house spider feels threatened or detects prey, it may exhibit a rapid lunge or a quick burst of speed. This sudden acceleration can appear like a jump to an observer, especially given the spider’s small size and reaction speed. However, these are fast runs or lunges, not true leaps where the spider propels itself entirely into the air.
Another behavior that can be misinterpreted is a controlled fall from a web or surface. A spider might release its grip and drop a short distance on a silk thread, which can look like a jump, particularly if it then quickly regains its footing. These sudden movements, due to their small size and burst-like energy expenditure, contribute to the misconception of jumping.
The Actual Jumpers
In contrast to house spiders, true jumping spiders, belonging to the family Salticidae, are capable of leaps. These spiders possess distinct characteristics, including a compact, often hairy body and large, forward-facing eyes that provide excellent vision and depth perception. Their eyesight is crucial for hunting, allowing them to stalk and precisely pounce on prey.
Jumping spiders do not rely on large leg muscles like insects for their powerful jumps. Instead, they utilize an internal hydraulic system that rapidly increases blood pressure in their legs. This sudden surge of hemolymph (spider “blood”) extends their legs, propelling them through the air for distances up to 50 times their body length. Before a jump, they attach a silk dragline to the surface, which serves as a safety line, allowing them to recover if they miss their target.