Is a Bald Patch on Your Tarantula a Sign of Stress or Something Else?

If you're new to tarantula keeping, spotting a bald patch on your spider’s abdomen, especially one that starts to darken, can raise alarm bells. Some people will tell you it’s a sign of stress. But in most cases, they’re wrong.

So, let me break it down clearly:
A dark bald patch on a tarantula’s abdomen is usually a natural part of the molting process, not a sign your pet is stressed.

What Causes the Bald Spot?

Most New World tarantulas (like Brachypelma, Grammostola, or Aphonopelma species) have urticating hairs, tiny, barbed hairs they kick off as a defense mechanism.

These hairs come from the abdomen. Repeated flicking, even just from minor disturbances, can cause a bald spot. It doesn’t hurt them, and it’s totally normal. Once the patch is exposed, you might start seeing a color change.

What Does the Dark Patch Mean?

When the bald spot turns dark, ranging from yellow-white to slate-grey to nearly black, it’s a strong sign the tarantula is preparing to molt. This is called a pre-molt phase.

Inside their exoskeleton, a new one is forming. The darkening you see is that new skin becoming visible as the outer layer thins. Amazing stuff!

Common signs of pre-molt include:

• Refusing food

• Sluggish or hiding behavior

• Sealing off their burrow or hide

• Lying in a strange position (even on their back before the molt)

The darker the spot, the closer they are to shedding. So if your tarantula’s got a bald, black patch on its bum and has gone off food, congrats, you’re likely about to witness a molt.

When Is a Bald Patch a Problem?

There are rare cases where a bald patch could reflect stress—but only if it comes with other symptoms.

Signs of a stressed tarantula include:

• Constant pacing or trying to climb glass

• Staying out in the open all the time and not really moving

• Flicking hairs constantly, even at nothing

• Curled or tucked legs (dehydration or illness)

• Lethargy outside of pre-molt

In these cases, you should review your setup:

• Is humidity and temperature correct?

• Is there a proper hide?

• Is the enclosure too large or barren?

• Are you handling them too often?

But again, a dark bald spot by itself is almost never a red flag.

Final Word

If your tarantula has a bald, dark abdomen, don’t panic—it’s likely just prepping for a molt. This is part of their natural cycle and usually means you’re doing things right. Make sure they’re left alone, humidity’s stable, and enjoy the fascinating process when it happens.