Tarantulas are large, recognizable spiders belonging to the family Theraphosidae, identified by their substantial size and prominent hairiness. With over 1,000 species worldwide, these arachnids display a broad spectrum of physical characteristics. A visual examination reveals a complex structure of body segments, specialized appendages, and a variety of textures and colors.
Basic Anatomy and Body Proportions
Like all spiders, a tarantula’s body is divided into two primary sections: the cephalothorax (prosoma) and the abdomen (opisthosoma). The cephalothorax is the fused head and midsection where all appendages originate. The abdomen is the larger, more bulbous rear section of the body.
The two body parts are connected by a narrow, flexible stalk called the pedicel, which allows the abdomen a wide range of motion. Four pairs of robust walking legs are attached to the prosoma, giving the tarantula its characteristic eight-legged stance. These legs are typically thick and powerful, contributing to the spider’s heavy-bodied look.
Scale and Defining Textures
Tarantulas are known for their dimensions, with size measured by the span of their legs. The leg span of most species ranges from approximately 3 inches to 12 inches, with body lengths between 2 and 4.5 inches. The largest species, such as the Goliath birdeaters, can reach dimensions comparable to a dinner plate.
The defining visual texture is a dense covering of fine, bristle-like hair, or setae, across the entire body and legs. These hairs create a fuzzy or velvet-like appearance, especially on the abdomen. Many New World tarantulas possess specialized urticating hairs on their abdomen. These barbed bristles can be flicked as a defense mechanism, distinguishing them from the general sensory hairs.
Specialized Features: Fangs, Eyes, and Pedipalps
The front of the cephalothorax features specialized appendages for feeding and sensing. The mouthparts, called chelicerae, house the fangs, which are large and prominent. Tarantulas are distinguished by the orientation of their fangs, which are parallel to each other and point straight down. This arrangement differs from the pincer-like fangs found in many other spider groups.
Tarantulas possess eight small eyes, clustered together on a raised mound called the ocular tubercle at the front of the carapace. Vision is not sharp, serving primarily to detect movement and light changes. Flanking the chelicerae are the pedipalps, a pair of shorter, leg-like appendages. These structures are used for manipulation, helping the spider hold and turn prey, and they also function as sensory organs.
The Spectrum of Color and Pattern
While many tarantula species feature cryptic coloration in shades of brown, black, or tan, the family exhibits a wide range of striking visual diversity. Some species display dramatic patterns and vivid hues.
Examples of Coloration
The Cobalt Blue tarantula is known for its iridescent blue coloration on its legs and abdomen. The Mexican red-knee tarantula features contrasting bands of vibrant red-orange on its legs against a black body.
Coloration can also appear metallic. The Sapphire Ornamental tarantula possesses a bright, shimmering blue on its legs and carapace. The Greenbottle Blue tarantula showcases a combination of colors, typically featuring a metallic blue carapace, vibrant green legs, and a bright orange abdomen. Many Old World species are known for their vivid hues, often utilizing aposematism to signal their presence.