Baby jumping spiders, called slings (short for spiderlings), are among the most appealing tiny animals you'll ever keep. They're miniature versions of the adults, complete with the head-tilting curiosity and big-eyed stare, just at a fraction of the size. A freshly hatched Phidippus regius sling is about 2-3mm long. They're absurdly small.
They're also more fragile than adults, and the care differences, while not dramatic, matter enough that it's worth covering them separately. If you've bought a sling or are thinking about it, this covers the important bits.
Enclosure
Small. Really small. A sling in a large adult enclosure won't thrive because it can't find its food. Prey items wander off into corners and the spider never encounters them. For first and second instar slings, a deli cup or small clear container about 5-8cm across works well. Poke ventilation holes with a heated pin (not a drill, you'll make holes too large and they'll escape through them).
Put a small piece of cork bark or a fake leaf in there for the sling to build its first retreat under. That's it for decoration. You'll upgrade as they grow.
As the spider grows through instars, size up the enclosure gradually. Third and fourth instar spiders can move to something about 10x10x15cm. Sub-adults and adults need the full 20x20x30cm arboreal setup. The principle throughout is the same: enough space to hunt but not so much they lose track of prey.
Temperature
Same range as adults: 22-28C. Slings are actually a bit more tolerant of temperature fluctuation than people assume, but consistent warmth helps them grow steadily and moult on schedule. In a UK home, room temperature is often too cool. A heat mat on the side of the enclosure works, but with small containers, be careful. A heat mat designed for a 30cm enclosure can overheat a 5cm deli cup in minutes. Use a thermostat. Always.
Some keepers place sling containers near (not on) a heat source, or in a warm room rather than directly heating each tiny cup. If you're raising multiple slings, a heated shelf or warm cabinet at a stable 24-25C is a practical solution.
Humidity
Slings are more vulnerable to dehydration than adults because of their higher surface-area-to-volume ratio. They dry out faster. Mist one side of the container lightly every 1-2 days. You want tiny water droplets on the walls for them to drink from. Don't soak the enclosure. A waterlogged container is just as dangerous as a dry one for a sling, and standing water can actually trap and drown very small spiderlings.
Ventilation is still necessary. Stagnant air plus moisture equals mould, and mould in a sling container can overwhelm a tiny spider. The goal is light, regular misting with decent airflow. If you see mould growing, increase ventilation and reduce misting frequency.
Feeding
This is where sling care gets fiddly. The prey has to be small enough for the spider to catch and overpower. For most jumping spider slings, that means flightless fruit flies (Drosophila melanogaster) and nothing else for the first few instars. Melanogaster fruit flies are about 2mm long, which is appropriate for a 3mm spider.
Drop one or two flies into the container every 2-3 days. Watch whether the sling catches them. If the flies are still wandering around after 24 hours, remove them. A fruit fly can't hurt a sling, but a buildup of dead flies in a tiny container creates hygiene problems quickly.
As the spider grows, graduate to D. hydei (larger fruit flies, about 3-4mm) around the third instar. By the fourth or fifth instar, they can usually handle small houseflies or micro crickets. The rule of thumb remains the same: prey no larger than the spider's abdomen.
Slings that refuse food are usually in pre-moult. Leave them alone. Slings moult frequently, sometimes every 2-3 weeks if they're warm and well-fed. A fasting period of a week is normal pre-moult. Two weeks is fine. Panic after three.
Moulting
Sling moults happen often and are generally straightforward. The same rules apply as for adults: don't disturb them, maintain humidity, remove uneaten prey. Because slings are smaller, the moult itself is quicker. They might be in and out of the process within an hour or two.
Failed moults in slings are uncommon if humidity is adequate. When they do happen, there's very little you can do at this size. The spider is too small for any meaningful intervention. This is one reason maintaining proper humidity is so much more important with slings than "optional extra" territory.
Common sling problems
Escape. By far the most common issue. Slings are tiny and fast. Any gap larger than about 1mm is an exit. Check ventilation holes carefully. Mesh gaps, lid seals, feeding port covers. If there's a way out, they'll find it, usually within the first 48 hours.
Dehydration. Shrivelled abdomen, reduced activity, reluctance to eat. Mist the enclosure walls immediately. If the sling perks up within a few hours, adjust your misting schedule. If it doesn't improve, the prognosis isn't great.
Mould. White fuzzy growth on uneaten prey, substrate, or the sides of the container. Remove the mouldy material, improve ventilation, and reduce misting slightly. A bit of white mould is common and generally harmless. Green or black mould is a bigger concern and usually means the container needs a full clean.
Not eating. Usually pre-moult. Could also be that the prey is too large (try smaller flies), the temperature is too low (check your heat source), or the sling is stressed from recent disturbance (leave it alone for a few days).
When to start handling
Most keepers wait until at least the sub-adult stage before attempting handling. Slings are genuinely too small and fast to handle safely. They can disappear into a fold of clothing or a gap in your fingers in a fraction of a second. If you absolutely must interact with a sling, do it inside its enclosure or over a small, sealed space. A clear plastic tub inside a bathtub is a good insurance policy.
Be patient. They grow fast. A sling that seems impossibly tiny today will be a chunky sub-adult in a few months.