If you're wondering about the brazilian black tarantula size before bringing one home, you're looking at a spider that usually hits a solid 6 to 7 inches in diagonal leg span once it reaches full maturity. They aren't the absolute giants of the hobby—nothing like a Goliath Birdeater—but they have a substantial, heavy-bodied presence that makes them feel much larger than a spindly arboreal species of the same length.
In the tarantula keeping world, the Grammostola pulchra (its scientific name) is often called the "Labrador" of spiders. This is mostly because of its incredibly chill temperament, but also because it's just a solid, dependable-looking animal. It's got a jet-black, velvety appearance that looks stunning when they're full-grown. But getting to that 7-inch mark? That's going to take some patience.
The Long Road to Adulthood
One thing you should know right off the bat is that these guys grow incredibly slowly. If you buy a tiny spiderling (a "sling") that's only half an inch long, don't expect it to hit that impressive brazilian black tarantula size by next year. In fact, it might take five, six, or even eight years for a G. pulchra to reach its maximum dimensions.
Because they grow so slowly, they also live a very long time. Females can easily live for 20 years or more, while males usually tap out around 6 to 8 years. This slow-burn growth rate is actually a bit of a status symbol in the hobby. Because they take forever to get big, large adults are often quite expensive. You're essentially paying for the years of care and feeding someone else put in to get that spider to a majestic size.
Measuring by Diagonal Leg Span
When we talk about tarantula size, we almost always use "Diagonal Leg Span" (DLS). This is measured from the tip of the front left leg to the tip of the back right leg (or vice versa). So, when someone says a Brazilian Black is 6 inches, they don't mean the body is 6 inches long—that would be a terrifyingly huge spider.
The body itself (the cephalothorax and abdomen) might only be about 2.5 to 3 inches long. However, because G. pulchra is a terrestrial, "heavy-bodied" species, they look thick. They have chunky legs and a very round, bulbous abdomen if they're well-fed. They carry their weight well, giving them a very "sturdy" feel compared to the skinnier, more athletic-looking species you might see.
Male vs. Female Size Differences
In the spider world, the girls usually run the show, and that's definitely true here. Females are the ones that hit that 6-7 inch mark and stay bulky throughout their lives. They are the "showpieces" of a collection because of their size and longevity.
Males, on the other hand, are a bit different. Once a male hits maturity, he'll usually be a bit smaller and leggier. He doesn't need to be bulky; he needs to be fast to find a mate. A mature male might have a decent leg span, but his body will look much smaller and "scrawnier" than a female of the same age. Once they reach that final "ultimate" molt, they stop growing entirely and focus all their energy on finding a girlfriend.
How Size Affects the Enclosure
Because the brazilian black tarantula size is fairly significant, you can't just keep an adult in a tiny plastic deli cup. While they aren't the most active spiders—they spend a lot of time just sitting there looking pretty—they still need enough room to move around.
A standard 5 to 10-gallon glass tank or a large acrylic enclosure usually does the trick for an adult. A good rule of thumb is that the floor space should be at least 3 to 4 times the leg span of the spider in length and 2 to 3 times the leg span in width.
One thing people often forget is that height is actually a danger for a spider this size. Because they are heavy-bodied, a fall can be fatal. If a 7-inch Brazilian Black climbs to the top of a tall cage and loses its grip, its abdomen can rupture like a water balloon. You want to make sure the "fall zone" is minimal—fill the enclosure with plenty of substrate so that there's only a few inches of space between the dirt and the lid.
Feeding for Growth
Does feeding them more make them get to that 7-inch size faster? To an extent, yes. "Power feeding" is a term some keepers use where they offer food more frequently to speed up the molting cycle. However, since G. pulchra is genetically predisposed to be a slow grower, there's only so much you can do.
Most keepers find that a juvenile or adult does perfectly fine with a couple of large crickets or a single Dubia roach every week or two. If they get too fat, their abdomen will look disproportionately large compared to their legs, which again, increases the risk of injury if they happen to take a little tumble.
The Molting Process and Size Jumps
Tarantulas don't grow gradually like we do. They grow in "bursts" through a process called molting. They'll crawl out of their old skin, and for a few hours, they're soft and slightly larger than they were before.
It's always a shock to see the size difference after a successful molt. Your spider might go into its hide looking like a 4-inch juvenile and emerge a few weeks later looking significantly closer to its adult brazilian black tarantula size. During this time, they're very vulnerable, so it's important not to bother them or leave live prey in the tank that could nibble on their soft, new skin.
Why Size Doesn't Mean Scary
For some people, a 7-inch black spider sounds like the stuff of nightmares. But in the world of tarantula keeping, the Brazilian Black is the ultimate "beginner" species because its size is matched by its docility. They are generally very slow-moving and rarely show any defensive behavior.
Because they are so large and sturdy, they are also easier to manage than tiny, teleporting spiders that can disappear into a crack in the floorboards in a split second. Their size makes them easy to keep track of, and their predictable movements make them a joy to observe.
Final Thoughts on the Brazilian Black
If you're looking for a spider that makes a statement without being unmanageable, the Brazilian Black is a perfect choice. That 6 to 7-inch leg span, combined with that deep, coal-black color, makes them one of the most beautiful pets you can own.
Just remember that you're playing the long game. You won't get a giant overnight. But watching a tiny, brown-ish spiderling slowly transform over the years into a massive, jet-black adult is one of the most rewarding parts of the hobby. It's a slow process, but once you see that full brazilian black tarantula size in person, you'll realize it was well worth the wait. They're basically the crown jewels of any tarantula collection, and their impressive size is just the icing on the cake.