The sight of an eight-legged creature often sparks a mix of fascination and apprehension, especially when it comes to tarantulas. Many people wonder if tarantulas are distinct from spiders, or if they are simply a specific kind of spider. While all tarantulas are classified as spiders, it is important to recognize that not all spiders are tarantulas.
The Arachnid Family Tree
Spiders and tarantulas belong to the class Arachnida, a group that also includes scorpions, mites, and ticks. Within Arachnida, spiders form a distinct order known as Araneae. Every spider, including every tarantula, is an arachnid.
The order Araneae is further divided into suborders. Tarantulas fall under the suborder Mygalomorphae. This classification sets them apart from “true spiders,” which belong to the suborder Araneomorphae. Tarantulas represent an ancient lineage within the spider family tree, distinct from many web-building or actively hunting spiders.
Key Characteristics of Tarantulas
Tarantulas have several distinct features. They are recognized by their large, robust bodies and dense covering of hair-like structures called setae. These spiders can range significantly in size, with leg spans from 4.5 to 11 inches, and some species weighing several ounces.
A defining characteristic of tarantulas is the orientation of their fangs, known as chelicerae. Unlike many other spiders whose fangs cross in a pincer-like action, tarantula fangs point downwards and strike in a parallel, stabbing motion. Tarantulas have relatively long lifespans, particularly females, which can live for 20 to 30 years, while males typically live 7 to 12 years. Most tarantulas are burrowing spiders, creating silk-lined retreats in the ground, though some species are arboreal and live in trees.
Shared Spider Traits
Despite their unique characteristics, tarantulas share many fundamental traits with all other spiders. All spiders, including tarantulas, have eight legs. Their bodies are divided into two main segments: the cephalothorax (or prosoma), a fused head and thorax, and the abdomen (or opisthosoma). These two body parts are connected by a narrow waist called a pedicel.
All spiders possess chelicerae, mouthparts equipped with fangs used to inject venom into prey. They also have pedipalps, a pair of appendages near the mouth that resemble small legs. Pedipalps are used for various functions like touching, manipulating prey, and in males, for reproduction. All spiders produce silk from spinnerets, though its utilization varies among species.
Beyond Physical Differences
Beyond their anatomical distinctions, tarantulas exhibit behavioral and ecological differences from many other spiders. Tarantulas are often ambush predators, waiting for prey to come within striking distance rather than building elaborate webs to capture food. They primarily prey on insects and other small arthropods, though larger species may occasionally consume small vertebrates. While all spiders possess venom, tarantula venom is mild and less potent to humans compared to some other medically significant spider species.
Tarantulas employ distinct defensive mechanisms. Many New World tarantulas, found in the Americas, possess urticating hairs on their abdomen. When threatened, they flick these barbed hairs into the air using their hind legs, causing irritation to potential predators. Old World tarantulas, found in Africa, Asia, and Europe, lack these hairs and often rely on a more defensive posture, speed, and potentially more potent venom for protection. Tarantulas may also display threat postures, rearing up on their hind legs and exposing their fangs to appear more intimidating.