Moulting & Health

What moulting is

Like all arthropods, jumping spiders have a rigid exoskeleton that can't grow. To get bigger, the spider sheds its old exoskeleton and expands into a new, larger one. This is moulting (or ecdysis). Jumping spiders go through multiple moults in their lifetime, progressing through stages called instars. During each moult, the spider can't move, eat, or defend itself.

The spider splits its old exoskeleton along predetermined seam lines, pulls its body free (all eight legs, pedipalps, and fangs), and then expands the new, soft exoskeleton before it hardens. It's physically exhausting and risky every time.

Signs of pre-moult

Learning to spot pre-moult is one of the most useful things you can do as a keeper. The signs usually show up days before the actual moult:

• Colour looks dull or faded. The new exoskeleton developing underneath makes the old one look washed out.
• Abdomen may darken noticeably
• Refuses food. The spider stops hunting and loses interest in prey.
• Less active overall, with reduced movement and exploration
• Retreats into a web sac (a dense silk hammock or enclosure) for an extended period. This is the moult chamber.

These signs can appear anywhere from a few days to a week or more before the moult. Juveniles moult more frequently than adults, sometimes every few weeks during rapid growth.

What to do

• Make sure humidity is adequate, 60 to 70%. Lightly mist the enclosure (not the spider or its web sac) to raise humidity if needed. The spider needs moisture to soften the old exoskeleton and slide free of it.
• Remove all live prey from the enclosure immediately. An uneaten cricket or fly can attack a moulting spider that can't defend itself.
• Leave the spider alone. Don't open or disturb the web sac. Don't touch the spider. Don't move the enclosure.

What NOT to do

This is where well-meaning keepers cause the most harm:

• Do NOT spray water directly on a moulting spider. Water droplets on a freshly moulted, soft-bodied spider can cause damage or trap it.
• Do NOT try to "help" remove the old exoskeleton. Any physical contact during moulting can tear the new, unhardened body. It's almost always fatal.
• Do NOT introduce prey. The spider can't eat during a moult and prey will harass it.
• Do NOT jostle or move the enclosure. Vibrations and sudden movements can cause the spider to panic and try to move before the moult is complete, leading to deformities or death.

The best thing you can do during a moult is nothing. Seriously. Any disturbance can cause a failed moult, which is usually fatal.

Failed moults

A failed moult happens when the spider can't fully free itself from its old exoskeleton. The most common causes:

• Not enough humidity. The old exoskeleton doesn't soften enough for the spider to pull free.
• Physical disturbance during the moult, whether vibration, handling, or prey interference.
• The spider being too weak, usually from being underfed or dehydrated in the weeks before the moult.

A spider stuck in its old exoskeleton will usually die. Legs may be trapped, the body may be only partially out, or the spider may have freed itself but with deformed or missing limbs. Once a moult has failed, there's very little you can do. Intervention rarely works and often makes things worse. The only reliable approach is prevention: proper humidity, good feeding, and zero disturbance.

Post-moult care

After a successful moult, your spider will be pale and noticeably soft. The new exoskeleton takes time to harden and darken to its normal colouration.

• Do NOT feed for 24 to 48 hours. The spider's fangs (chelicerae) need to fully harden before it can bite and subdue prey. Feed too soon and the spider may try to strike but can't puncture the prey, or worse, damages its own soft fangs.
• Make sure water is available. Lightly mist one side of the enclosure so the spider can drink when it's ready.
• Resume feeding once the spider shows active interest. You'll see it start exploring and tracking movement again when it's ready to hunt.

The old exoskeleton (exuvium) can be left in the enclosure or removed. It's harmless either way. Some keepers collect exuviae because they can be used to identify the spider's sex once it reaches later instars.