Tarantulas are often the subject of exaggerated stories regarding their jumping ability. The true capabilities of tarantula movement are far more limited and grounded in their unique biology. They are adapted for stealth and short bursts of action, not for sustained, explosive leaps.
The Reality of Tarantula Movement
Tarantulas are not built for jumping like their smaller, specialized cousins, the jumping spiders. When a tarantula appears to jump, it is usually a rapid, short lunge or a controlled drop, typically covering only one or two times their body length. A large tarantula, with a leg span of four to six inches, might manage a horizontal burst of four to twelve inches at most. This movement is primarily used for immediate prey capture or a sudden, brief escape from a threat.
True vertical jumping is rare. However, some lighter, arboreal species, like the pink toe tarantula (Avicularia avicularia), are known to leap a few inches when startled or needing to bridge a small gap between branches.
The Role of Hydraulic Pressure in Locomotion
The limited jumping ability of tarantulas is rooted in their specialized method of leg extension. Unlike mammals, tarantulas lack extensor muscles in their primary leg joints. Instead, they rely heavily on hydraulic pressure generated by their body fluid, called hemolymph, to straighten their legs.
The spider increases pressure within its cephalothorax to force hemolymph into fluid-filled spaces within the legs. This surge of internal pressure extends the limbs, enabling walking and running. While this hydraulic system allows for powerful walking and climbing, its reliance on fluid pressure limits the speed and force required for explosive jumps.
Sudden Movements Mistaken for Jumps
The perception that tarantulas are adept jumpers often stems from their defensive behaviors, which involve rapid, sudden movements. When threatened, a tarantula may execute a sudden, short lunge toward the perceived danger. This is a burst of movement rather than a controlled jump.
Some New World tarantulas also employ a unique defensive action involving urticating hairs, which are irritating bristles on their abdomen. The spider uses its hind legs to quickly flick a cloud of these hairs at a threat. The rapid, jerky motion involved in this flicking contributes to the visual illusion of a sudden, uncontrolled jump or spasm.