Your female just sealed herself inside a heavily reinforced hammock. When you looked this morning there was a dense white mass visible through the enclosure wall. She laid an egg sac. The first instinct for most keepers is to do something, anything, to make sure it is okay. The correct instinct is almost the opposite: leave it alone, maintain stable conditions, and let her do what she already knows how to do.
This guide explains what is happening inside that silk bundle, what conditions support healthy development, and how to recognize the relatively rare situations where intervention is warranted.
Key Takeaways
- Do not open the enclosure or disturb the female while she is guarding the sac
- Maintain 24 to 28°C and moderate humidity (mist one wall lightly each day)
- A healthy Phidippus regius egg sac contains 30 to 200 eggs and incubates for 3 to 5 weeks
- Leave the female with her sac; maternal care improves hatch rates
- Separate slings into individual containers 3 to 7 days after they begin dispersing
What to Do When Your Jumping Spider Lays an Egg Sac
When a jumping spider lays an egg sac, do the following: stop opening the enclosure, maintain temperature at 24 to 28°C, mist one enclosure wall lightly once per day, continue offering food every 2 to 3 days (remove uneaten prey within a few hours), and wait. The incubation period is 3 to 5 weeks. Slings will emerge and begin dispersing; separate them individually at that point to prevent cannibalism.
What a Jumping Spider Egg Sac Looks Like
A healthy egg sac is a compact, firm-looking mass of white or off-white silk, usually round or oval and roughly pea-sized to grape-sized depending on species and clutch size. The female will have incorporated it into her hammock structure and in most cases it will be partially wrapped in additional silk layers.
Phidippus regius egg sacs are typically:
- 15 to 30 mm in diameter
- White to pale cream in color
- Firmly round, not deflated or wrinkled
- Located at the top or center of the hammock, usually attached to the enclosure wall or ceiling
The female positions herself on or near the egg sac and will face away from most disturbances. She is guarding it actively.
Signs of an unhealthy egg sac:
- Gray, brown, or black discoloration (indicates fungal growth or desiccation damage)
- Visibly deflated or collapsed structure
- Female has abandoned the hammock entirely and the sac sits unguarded and exposed
- Unusual musty odor (rare, but indicates mold)
A discolored sac does not automatically mean total loss. Some eggs within a partially compromised sac can still develop and hatch. Do not remove the sac prematurely.
How Many Eggs Does a Jumping Spider Lay?
The clutch size for Phidippus regius typically ranges from 30 to 200 eggs, with well-conditioned adult females averaging 80 to 120 eggs per clutch. The wide range reflects:
- Female age and instar: a first-clutch female lays fewer eggs than an experienced adult
- Nutritional condition at laying: a heavily conditioned female produces more eggs
- Species: smaller jumping spider species generally produce smaller clutches
- Whether the female was mated or laying unfertilized eggs
A portion of eggs in any clutch, often 20 to 40%, will be infertile or non-viable. This is normal and not an indicator of a problem with your husbandry.
Fertile vs. infertile egg sacs: An infertile egg sac tends to be smaller, more round and compact, and slightly lighter in color than a fertile one. However, these distinctions are not reliable enough to act on at a glance. Assume the sac is fertile and care for it accordingly until evidence says otherwise.
Incubation Conditions
Temperature
Keep the enclosure at 24 to 28°C (75 to 82°F) throughout incubation. Development slows noticeably below 22°C and can stall entirely. Above 30°C, desiccation risk and developmental failure increase. Stable temperature matters more than hitting a precise number.
If your home runs cooler, a small reptile or invertebrate heat mat set to the lower end of this range is appropriate. Do not place the enclosure directly on a heat mat without a thermostat, and do not place the mat underneath; use the side of the enclosure.
Humidity
Mist one wall of the enclosure lightly once per day. The goal is ambient humidity around 60 to 70%, not wet substrate. The egg sac itself should never be directly misted or waterlogged. You want the air to feel slightly humid, not damp.
A fully dry environment is more dangerous than a slightly wetter one. Dry air desiccates the egg sac and kills developing eggs. Excessively wet conditions encourage mold.
Light
Normal room lighting is fine. Direct sunlight is not: even a few hours of direct sun can overheat a small enclosure dramatically. Keep the enclosure out of direct sunlight throughout incubation.
The Do-Not-Disturb Rule
Do not open the enclosure to check on the egg sac. This is the most important and most frequently violated piece of egg sac care advice.
Each time you open the enclosure:
- The female is startled and may reposition or damage the egg sac
- Temperature and humidity fluctuate briefly
- In extreme cases, a stressed female will eat the egg sac
You can observe everything you need through the enclosure walls with a phone camera or a small magnifying lens held to the outside. If the sac looks white and round and the female is near it, everything is proceeding normally.
The only reasons to open the enclosure during incubation:
- You need to add water (mist briefly from an angle that avoids the hammock)
- You observe the female eating the egg sac (intervention is usually too late at this point)
- You see obvious mold growth spreading across the sac surface
Do not remove the egg sac from the female unless she has died. Jumping spider mothers actively regulate humidity around the sac by repositioning and adding silk layers. A motherless egg sac requires careful compensatory humidity management and survival rates are lower. If the female dies, maintain the sac at 70 to 75% humidity in a small sealed container with a damp cotton ball nearby.
Incubation Timeline
| Week | What Is Happening Inside | What You Should See Outside |
|---|---|---|
| Week 1 | Eggs laid; cell division begins | Sac visible in hammock; female guarding closely |
| Week 2 | Embryonic development underway | Sac unchanged externally; female may eat less |
| Week 3 | Embryos developing into pre-sling stage | Sac may look slightly fuller or unchanged |
| Week 4 | First instar slings fully formed inside | Sac unchanged externally |
| Week 4 to 5 | Slings emerge from the sac | Sac may twitch; tiny pale slings appear |
| Week 5 to 6 | Slings begin dispersing | Tiny spiders visible on enclosure walls |
These timelines assume 24 to 28°C. At the lower end of the range, add 1 to 2 weeks. At the higher end, development may complete slightly faster.
Feeding the Female During Incubation
Continue offering food to the female every 2 to 3 days during incubation. Some females will not eat at all while guarding; others eat normally. If she refuses prey, remove it promptly. Do not leave live insects in the enclosure with a guarding female.
A female that has guarded a clutch through to hatching has spent significant energy. Give her 4 to 6 weeks of heavy feeding (the same conditioning protocol used before mating) before considering a second pairing attempt.
When Slings Emerge
The first sign of imminent hatching is movement inside or near the egg sac. You may see the sac shifting slightly, or tiny pale shapes pressing against the silk interior. First instar slings (L1) are 1 to 2mm and nearly transparent.
Slings typically emerge over 24 to 72 hours, not all at once. They cluster initially, often still in or near the hammock. This clustering phase lasts 1 to 5 days.
Do not separate slings during the clustering phase. At this stage they are still largely passive and not yet hunting actively.
When to separate: Begin separating slings when they start moving independently away from the cluster. This typically happens 3 to 7 days after the first emergence. Once a sling moves purposefully around the enclosure rather than resting in the cluster, it is ready to be housed individually.
From this point, the critical challenge is keeping tiny spiders alive through their first several instars. For everything you need to know about that, see jumping spider sling care.
Frequently Asked Questions
Can I separate the egg sac from the female? Only if the female has died. Maternal care actively improves hatch rates. If you must remove the sac, keep it at 70 to 75% humidity in a small sealed container with a damp cotton ball positioned near (not touching) the sac.
My female ate the egg sac. What happened? Egg sac consumption is most common in females that were stressed during or after laying, poorly conditioned, or produced an infertile clutch. It also happens more often with first-time mothers. Some females simply do not exhibit maternal behavior reliably. This is not a failure of your husbandry in all cases.
The egg sac looks smaller than before. Is it collapsing? Slight size variation through observation is usually a trick of angle and light. If the sac is visibly deflated, gray, or wrinkled, this indicates desiccation. Increase humidity slightly and monitor through the enclosure wall.
My female is not eating while guarding. Is that normal? Yes. Many females fast partially or completely during the egg sac period. This is normal maternal behavior. Continue offering prey every 2 to 3 days and remove uneaten items promptly.
Do I need to artificially incubate the egg sac? Only if the female dies. Under normal circumstances, the female’s guarding behavior is part of what makes the incubation work.
How do I know if the sac is fertile? You often cannot know for certain until you see slings emerge or until the sac fails to produce any movement by week 6. Care for the sac as if it is fertile and wait.
For the full breeding process including conditioning and pairing, see how to breed jumping spiders. For what comes next after hatching, see jumping spider sling care.
The weeks between laying and hatching feel long. Resisting the urge to check on the egg sac every hour is genuinely difficult. But the keepers who end up with the highest hatch rates are usually the ones who opened the enclosure least.