Researched and written by the ExoPetGuides editorial team with AI-assisted drafting. All husbandry parameters and veterinary references independently verified.
What Is Molting and Why Do Jumping Spiders Do It?
Molting (ecdysis) is the process by which a jumping spider sheds its old exoskeleton to grow. Unlike vertebrates, whose bones grow continuously, arthropods are enclosed in a rigid external skeleton that cannot expand. The only way a jumping spider can increase in size is to split open its old cuticle, extract itself, and harden a new, larger exoskeleton underneath (source: Journal of Experimental Biology).
Every jumping spider molts multiple times throughout its life. Slings (spiderlings) molt most frequently because they are growing fastest. Adults of both sexes reach a terminal molt after which no further molting occurs. Male jumping spiders typically reach their terminal molt earlier than females and have shorter post-terminal lifespans.
Molting is the single most vulnerable period in a jumping spider’s life. The spider is immobile, defenseless, and physically fragile for hours during and after the process. Understanding what normal molting looks like, what can go wrong, and how to support your spider through each molt is fundamental to successful jumping spider keeping.
If your spider is approaching its first molt in your care, confirm that your enclosure setup supports the process. See the jumping spider enclosure setup guide for baseline requirements.
How Often Do Jumping Spiders Molt?
Molt frequency depends on age, species, feeding frequency, and temperature.
| Life stage | Approximate molt frequency | Notes |
|---|---|---|
| First instar (newborn) | Every 5-10 days | Rapid growth phase; molts are frequent and fast |
| Second to fourth instar (sling) | Every 10-20 days | Slowing slightly as the spider grows |
| Juvenile (fifth to eighth instar) | Every 3-6 weeks | Growth rate declines as the spider approaches maturity |
| Sub-adult (penultimate molt) | 4-8 weeks before terminal molt | The spider is nearing adult size |
| Adult (terminal molt complete) | No further molts | The final exoskeleton is permanent for the rest of the spider’s life |
Warmer temperatures (within the safe range of 24-29C) and frequent feeding accelerate growth and shorten the interval between molts. Cooler temperatures and less frequent feeding slow the process. Neither is inherently better; the spider’s biology adjusts to available resources.
Total molts in a lifetime: Most Phidippus regius individuals undergo 7-10 molts from hatching to terminal adult molt. Smaller species may complete fewer molts. Males typically reach their terminal molt in fewer instars than females of the same species.
Pre-Molt Signs: How to Know a Molt Is Coming
Recognizing pre-molt behavior allows you to adjust care (stop handling, ensure humidity, remove uneaten prey) before the molt begins. The pre-molt phase lasts 3-14 days depending on the spider’s age and size.
Reliable pre-molt indicators:
Food refusal. This is typically the first and most obvious sign. A spider that was eating enthusiastically every 2-3 days suddenly ignores or rejects prey. Pre-molt food refusal is normal and not a cause for concern unless it extends beyond 14 days without a molt occurring.
Darkened abdomen. As the new exoskeleton forms beneath the old one, the abdomen darkens noticeably. In species with lighter coloration (like female P. regius), you may see the abdomen shift from gray-brown to a deeper, more uniform dark tone. The darkening is caused by the new cuticle developing underneath.
Swollen abdomen. The abdomen may appear larger than usual as hemolymph (spider blood) accumulates in preparation for the hydraulic pressure needed to split the old exoskeleton.
Reduced activity. The spider becomes less active, spending more time in or near its silk retreat. Exploration, hunting, and visual tracking decrease.
Retreat reinforcement. Many jumping spiders thicken or seal their silk retreat before molting, creating a protected chamber. If your spider builds an unusually dense retreat and stops coming out, it is likely preparing to molt inside.
Dull coloration. The spider’s colors may appear washed out or muted as the old exoskeleton loosens from the new one underneath.
Important distinction: Pre-molt signs overlap with illness signs (lethargy, food refusal). The key differentiator is the abdomen. A pre-molt spider has a dark, full abdomen and retreats into its hammock. A sick spider typically has a normal or shrunken abdomen and may avoid the retreat. See the jumping spider health signs guide for detailed illness indicators.
The Molting Process: Step by Step
When a jumping spider is ready to molt, the process typically takes 15-60 minutes from the first visible split in the old exoskeleton to full extraction. The entire sequence, including the hardening phase, spans several hours.
Phase 1: Positioning
The spider positions itself inside its silk retreat, usually hanging from silk threads or lying on its back. Lying on its back is the most common molting position for jumping spiders and is perfectly normal. Do not assume a spider on its back is dead or in distress if it is in the expected molt timeframe.
Phase 2: Exoskeleton Split
The old exoskeleton (exuvium) splits along the cephalothorax, usually at the front margin between the carapace and the sternum. This split is driven by increased hemolymph pressure as the spider pumps fluid from the abdomen into the cephalothorax.
Phase 3: Extraction
The spider slowly extracts itself from the old exoskeleton, pulling its legs, pedipalps, chelicerae, and abdomen free one section at a time. This is the most critical and dangerous phase. If the new cuticle is too dry or the old one adheres too tightly, the spider can become stuck (dysecdysis).
During extraction, the spider is extremely fragile. The new exoskeleton is soft and pliable. Any physical contact or vibration can damage the spider’s body or cause it to tear the new cuticle.
Phase 4: Expansion
Immediately after extraction, the spider pumps hemolymph into its legs and body to expand to its new, larger size while the cuticle is still soft. This expansion must happen before the new exoskeleton hardens. If the spider is disturbed during this phase, it may harden in a deformed position.
Phase 5: Hardening (Sclerotization)
The new exoskeleton gradually hardens over 24-48 hours. During this period, the spider remains in its retreat, and its colors gradually intensify as pigments develop in the new cuticle. The spider will not eat until the new chelicerae (fangs) are fully hardened, which takes approximately 2-3 days.
How to Support Your Spider During a Molt
Your primary role during a molt is to provide the right conditions and then leave the spider completely alone.
Before the Molt (Pre-Molt Care)
Stop handling. Once you notice pre-molt signs, do not handle the spider until the molt is complete and the new exoskeleton has hardened (typically 3-5 days post-molt). Handling a pre-molt spider can cause injury and molt failure.
Remove uneaten prey. Live feeder insects in the enclosure can injure or stress a molting spider. A cricket can literally eat a soft-bodied, immobile spider mid-molt. Remove all uneaten feeders when pre-molt signs appear.
Maintain humidity. Adequate humidity is critical for a successful molt. The moisture helps the old exoskeleton separate cleanly from the new one. For most Phidippus species, maintain 55-65% humidity during the pre-molt and molt period by misting the enclosure once daily. Do not mist directly into the spider’s retreat.
Maintain temperature. Keep the enclosure within the normal 24-29C range. Temperature fluctuations during the molt can slow or stall the process.
Do not rearrange the enclosure. Leave all decorations, structures, and the silk retreat exactly where they are. The spider has positioned itself deliberately for the molt.
During the Molt
Do not intervene. This is the hardest rule for new keepers, but it is the most important one. Do not open the enclosure, do not mist, do not check on the spider, do not take photos with flash. Vibrations from the enclosure door opening can disrupt the process. The spider needs to complete the molt without any external interference.
How long to wait: If you see the spider on its back and suspect molting has begun, give it a minimum of 6-8 hours before checking. Most successful molts complete within 1-2 hours, but the hardening phase extends for many more hours during which the spider should not be disturbed.
After the Molt (Post-Molt Care)
Do not feed for 2-3 days. The spider’s chelicerae and fangs need to harden before it can safely bite and consume prey. Offering food too early can damage the soft fangs. Wait until the spider begins showing hunting interest (tracking prey through the glass, adopting a stalking posture) before offering a small feeder.
Increase misting slightly. Post-molt spiders may drink more as they replenish hemolymph. Provide fresh water droplets daily for the first 3-5 days after molting.
Do not handle for 3-5 days. The new exoskeleton needs time to fully harden. A post-molt spider that appears active and alert may still have a soft cuticle. Wait until the spider has eaten at least one meal before resuming handling.
Leave the exuvium (shed skin). The old exoskeleton left behind in the retreat is harmless and can be removed during the next enclosure cleaning. Some keepers collect exuvia to track molt history and confirm sex (mature male exuvia show enlarged pedipalps). For sex identification, see male vs female jumping spider.
Molt Failure (Dysecdysis): Causes and Emergency Response
Dysecdysis is a failed or incomplete molt where the spider cannot fully extract itself from the old exoskeleton. It is the second most common cause of death in captive jumping spiders after dehydration.
Causes of Dysecdysis
Insufficient humidity. The most frequent cause. Low humidity causes the old exoskeleton to dry and adhere to the new cuticle, preventing clean separation. This is why maintaining 55-65% humidity during the molt period is critical.
Physical disturbance. Vibrations, handling, or opening the enclosure during molting can interrupt the process and cause the spider to freeze or panic, resulting in incomplete extraction.
Nutritional deficiency. A spider that has been underfed or fed a nutritionally poor diet may not have the hemolymph volume or cuticle integrity needed for a successful molt. Consistent, varied feeding in the weeks before a molt supports cuticle formation (source: Journal of Arachnology).
Dehydration. A chronically dehydrated spider enters the molt with insufficient hemolymph to generate the hydraulic pressure needed to split the old exoskeleton.
Mites or parasites. External mites can interfere physically with the molting process and introduce secondary infections during the vulnerable soft-body phase.
Injury. A spider with previous leg injuries or exoskeleton damage may struggle to extract the injured area from the old cuticle.
What Dysecdysis Looks Like
- The spider is partially out of its old skin but has stopped progressing for more than 4-6 hours.
- One or more legs remain trapped in the old exoskeleton.
- The spider appears deformed or misshapen after the molt attempt.
- The spider is motionless and encased for an extended period.
Emergency Intervention
Step 1: Raise humidity immediately. Mist the enclosure to bring humidity to 70-75%. Partially cover ventilation holes with damp paper towel if needed. The goal is to soften the old cuticle so the spider can continue extracting.
Step 2: Do not pull the old skin off manually. This is critical. The old and new exoskeletons may still be connected at points, and pulling can tear the new cuticle or rip legs off. Manual intervention almost always makes things worse.
Step 3: Wait and observe. Give the spider 6-12 hours in the elevated humidity environment. Many stuck molts resolve on their own once the old cuticle softens.
Step 4: If no progress after 12 hours. The situation is critical. Consult an exotic vet experienced with invertebrates. Some vets can carefully assist with stuck molt removal under magnification, but success rates are variable.
Step 5: Accept possible outcomes. A spider that survives a stuck molt may lose one or more legs. Lost legs can regenerate during subsequent molts in juveniles but not after the terminal adult molt. A spider that cannot free itself at all within 24 hours is unlikely to survive.
Molt Frequency by Species
| Species | Total lifetime molts | Terminal molt age (approximate) | Notes |
|---|---|---|---|
| Phidippus regius (regal) | 7-10 | Males 4-6 months, females 6-9 months | Largest common pet species; molts are more visible |
| Phidippus audax (bold) | 7-9 | Males 4-5 months, females 6-8 months | Similar to regius |
| Hyllus diardi (heavy jumper) | 8-11 | Males 6-8 months, females 8-12 months | Larger species; longer growth period |
| Hasarius adansoni (adanson’s) | 6-8 | Males 3-4 months, females 4-6 months | Smaller species; reaches maturity faster |
These ranges are approximate and influenced by temperature, feeding frequency, and individual variation. A well-fed spider in a warm enclosure molts faster than a lightly fed spider in a cooler environment.
Post-Molt Growth and Color Changes
After each molt, the spider is slightly larger than before. The size increase is most dramatic in early instars (slings can nearly double in body length after a molt) and becomes more incremental as the spider approaches adulthood.
Color changes to expect:
- Freshly molted spiders appear pale and translucent. Colors develop over 24-48 hours as the cuticle hardens and pigments express.
- Each molt may reveal subtle color changes. Juvenile male P. regius, for example, develop progressively darker black coloration and more vivid chelicera iridescence with each molt as they approach sexual maturity.
- The final (terminal) molt produces the adult coloration that remains for the rest of the spider’s life. This is when sex-specific coloration becomes most pronounced.
Leg regeneration: If a jumping spider lost a leg prior to molting, the new leg will begin to regenerate during the molt. The regenerated leg is typically slightly smaller and thinner than the original but becomes more normal with subsequent molts. Regeneration is only possible in pre-terminal molts. After the terminal adult molt, lost legs are permanent. For information on leg loss and health assessment, see the jumping spider health signs guide.
Frequently Asked Questions
How long does it take a jumping spider to molt?
The active molting process (from the first exoskeleton split to full extraction) typically takes 15-60 minutes. The full cycle, including positioning, extraction, expansion, and initial hardening, spans 4-8 hours. Complete cuticle hardening takes 24-48 hours after extraction. Do not disturb the spider during any of these phases.
Is my jumping spider dead or molting?
A molting spider lies on its back (often inside its silk retreat), is motionless, and may appear pale or oddly shaped as it extracts from the old skin. A dead spider also lies motionless with legs curled under. The key difference: a molting spider is typically inside or near its retreat, and you may see the old exoskeleton partially split or separated from the body. A dead spider outside its retreat with fully curled legs and no visible exuvium is unlikely to be molting.
Should I help my jumping spider molt?
No. Under normal circumstances, you should never intervene during a molt. The only exception is if the spider is clearly stuck in a partial molt for more than 4-6 hours, in which case you should raise humidity to 70-75% and wait. Never manually pull old exoskeleton off the spider.
How do I know when my jumping spider is done molting?
The spider has completed the molt when it is fully separated from the old exoskeleton (exuvium) and begins to move, even slowly. Full recovery takes 2-3 days, during which the spider rests in its retreat, its colors develop, and its cuticle hardens. The spider signals full recovery by resuming hunting interest and active exploration.
Why did my jumping spider die during molting?
The most common causes of molt death are insufficient humidity (old cuticle adheres to new one), physical disturbance during the process, and pre-existing dehydration reducing hemolymph pressure. Ensuring stable 55-65% humidity, removing all feeder insects before the molt, and leaving the spider completely undisturbed give it the best chance.
Can adult jumping spiders still molt?
No. Jumping spiders undergo a terminal (final) molt upon reaching sexual maturity. After this molt, the exoskeleton is permanent for the rest of the spider’s life. This means adult injuries (leg loss, cuticle damage) cannot regenerate. Males reach their terminal molt before females in most species.
How many times does a jumping spider molt in its life?
Most pet jumping spider species molt 7-10 times from hatching to their terminal adult molt. The exact number varies by species, sex, feeding regime, and environmental temperature. Males typically undergo fewer total molts than females.
Sources
- Journal of Experimental Biology https://journals.biologists.com/jeb – arthropod ecdysis mechanics and cuticle formation
- Journal of Arachnology https://www.americanarachnology.org/journal-joa/ – Salticidae growth stages and molt frequency
- PetMD https://www.petmd.com/exotic/care/jumping-spider – captive jumping spider molt care
- Arachnoboards.com community – molt observation records and dysecdysis troubleshooting
- University of Florida Entomology Department – arthropod cuticle biology and sclerotization
Editorial Disclosure
This article was researched and written by the ExoPetGuides editorial team with AI-assisted drafting. All molting information was verified against arachnological literature and experienced keeper observations. ExoPetGuides does not sell spider care products and has no affiliate relationship with any brand mentioned in this article.
This guide provides general husbandry information based on current species-authority consensus. It is not a substitute for professional veterinary advice. If your jumping spider is experiencing a stuck molt or post-molt complications, consult a qualified exotic veterinarian experienced with invertebrates.