Tarantula Anatomy 101

SUNDAY, APRIL 22, 2018   |   POSTED BY MICAH GARTMAN

Sydney Sue has been a bundle of energy the past few weeks. He spends his days and nights digging holes, climbing the walls and generally making a mess of his house. He's still not showing any signs of being in pre-molt. It's been 565 days since he last "changed his clothes."

He has also been experimenting with escaping from his enclosure. He's not yet strong enough to lift the lid off his house but we'll definitely be locking the roof down before his next molt.

In this video, a Brachypelma smithi—the Mexican Red Knee tarantula—shows how powerful it can be when she wants to explore the world:

During one of his recent reconnoiter missions I was able to take this photo of Sydney Sue's "ventral" side. As you can see, tarantulas are made up of lots of parts. Click on the photo for a larger version:

This illustration from Tarantulas US shows the location and scientific name of each part:

The most infamous parts of a tarantula are its fangs. The fangs are multi-purpose tools. Sydney Sue uses his fangs for biting tasty crickets, digging holes and flipping over his water bowl.

A tarantula's fangs are EXTREMELY sharp and work like a hypodermic needle. Each fang is hollow and attached to a venom gland. The tarantula squeezes muscles in its prosoma (the tarantula's head) to force the toxic liquid through the fangs. The venom exits through a venom hole and into their prey. As you can see in this photo of a Cyclosternum fasciatus—the Costa Rican Tiger Rump tarantula—the venom hole is not at the tip of the fang. Instead, it's just above the tip. This prevents the hole from being accidentally clogged as the fangs pierce a prey's shell.

The fangs are attached to a set of jaws called chelicerae (pronounced cuh-LISS-er-ee). The tarantula uses its chelicerae to grind up its food before eating it. Tarantulas cannot eat solid food—only soupy liquids. Once the food is properly mashed the tarantula slurps it up into its mouth. Here you can see the fangs, chelicerae and mouth of a Pamphobeteus ultramarinus—the Ecuadorian Birdeater tarantula:

The next well-known feature of a tarantula are its legs. A tarantula's legs are divided into seven segments. Each segment is connected to the others by a series of long, thin muscles. When a tarantula wants to walk, it pushes its "blood" (called hemolymph) into its legs. The tension from the muscles combined with the pressure from the hemolymph allow the tarantula's legs to move. In other words, they're hydraulic—which explains why they look so silly when they walk.

In the wild, a tarantula may lose a leg during a fight, while mating or when defending themself from a predator. It is common for a tarantula to pull off a damaged limb if it is no longer useful. What's amazing is that the tarantula will grow a new leg during its next molt!

Here we see a juvenile Brachypelma smithi missing two of its left legs:

In this photo, we see the freshly regenerated leg of another Brachypelma smithi:

The last tarantula part we'll look at is the opisthosoma (pronounced oh-PIZ-though-so-ma). We like to call it the "fuzzy butt." Inside the fuzzy butt are the tarantula's lungs, silk glands, reproductive organs and, uh, anus.

Yes, tarantulas poop.

A tarantula's opisthosoma is very delicate. It's a thin sac of fluid and organs—sort of like a water balloon. A fall from even a short distance could cause the opisthosoma to burst and would be fatal to the tarantula.

The opisthosoma is also where a tarantula's heart is located. Here we see the beating heart of Opadometa fastigata, a long-jawed orb weaver from Asia:

The opisthosoma of New World tarantulas—that is, tarantulas from North America, Central America and South America—appear to be covered in soft hairs. This couldn't be further from the truth. Those hairs are actually barbed bristles that tarantulas use for defense. If some of those bristles get in your nose or on your skin, you will sneeze and itch for days. Get them in your eye and you'll definitely need to seek urgent medical attention. Never touch the fuzzy butt!

Here is Sydney Sue modeling his fuzzy butt while eating a cricket:

To recap: Sydney Sue may escape, he's made up of hard-to-pronounce parts and has a fuzzy butt. And he poops.

Be nice to spiders :)

Bonus photo!

This is crazy! The tarantula in this photo is half boy and half girl. It's an extremely rare condition called gynandromorphia. Good luck pronouning that!

Spiders need love, too.
IUCN and CITES classify 37 species of tarantula as threatened or critically endangered.
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