Jumping spiders are hardy animals. Compared to many exotic invertebrates, they're forgiving of imperfect conditions and rarely get sick if the basics are right. But "rarely" isn't "never," and when something does go wrong, options for treatment are limited. There's no spider vet down the road. Most problems are easier to prevent than to fix, so knowing what to watch for matters. If your jumping spider looks sick, this is a good place to start.
Dehydration
This is the most common health problem in captive jumping spiders, and it's entirely preventable. A dehydrated spider has a shrivelled, wrinkled abdomen. It may be lethargic, reluctant to eat, and tucked into its retreat more than usual. In severe cases, the legs curl partially inward.
The cause is almost always insufficient misting. Jumping spiders drink from water droplets on the enclosure walls and decor. No droplets, no drinking. They won't use a water dish. Some keepers mist too infrequently, and others mist but with such poor ventilation that the water evaporates before the spider gets to it, or conversely, the air is so stagnant that mould grows before the spider drinks.
Fix: mist the enclosure walls lightly every 1-2 days. You should see small droplets forming on the glass. Ensure cross-ventilation so the air doesn't stagnate. If you catch dehydration early, most spiders recover within a day of being offered water droplets. Late-stage dehydration has a poor prognosis.
Failed moults
A moult that goes wrong is one of the leading causes of death in captive jumping spiders. The spider fails to fully extract itself from the old exoskeleton and gets stuck partway through. Sometimes they lose a leg. Sometimes they can't free the abdomen. Sometimes the new exoskeleton dries out in the wrong shape before the spider finishes pulling free.
Causes: low humidity is the primary culprit. The old exoskeleton needs to be supple enough to split cleanly, and dry air makes it stiff. Disturbance during the moult is another common cause. Vibrations, sudden temperature changes, or physical contact at the wrong moment can interrupt the process. Poor nutrition going into the moult weakens the spider's ability to complete it.
Prevention is everything. Maintain 50-70% humidity, remove live prey from the enclosure when you see pre-moult signs, and leave the spider alone. If a moult does fail, you can try increasing humidity around the spider and very gently softening stuck exuviae with a damp cotton bud, but be realistic about the odds. Many failed moults are fatal regardless of intervention.
Mould in the enclosure
Mould isn't a spider disease, but it creates conditions that can harm spiders. White, fuzzy mould on uneaten prey or substrate is common and usually harmless in small amounts. It's a sign of excess moisture or poor ventilation, which are the actual problems. Green or black mould is more concerning and indicates genuinely poor conditions.
A mouldy enclosure means the humidity-to-ventilation balance is off. Either you're misting too much, or there isn't enough airflow, or both. Remove visible mould, take out any decaying prey items, and improve ventilation. If the enclosure has become comprehensively mouldy, a full clean and rehouse is warranted.
Mould spores can irritate a spider's book lungs (their respiratory organs, located on the underside of the abdomen). Chronic exposure to a mouldy environment probably contributes to reduced lifespan even if it doesn't cause a single identifiable disease. Keep things clean.
Injuries from falls
Jumping spiders can survive falls that would seem dramatic for their size, but they're not indestructible. A fall from standing height onto a hard floor can rupture the abdomen or damage legs. The abdomen is particularly vulnerable because it's soft-bodied compared to the cephalothorax.
A spider with a ruptured abdomen will leak haemolymph (the arachnid equivalent of blood). Small leaks sometimes seal themselves with a clot, and the spider survives with a scar. Larger ruptures are usually fatal. There's no practical way to treat an abdominal rupture at home.
Leg injuries are more survivable. Jumping spiders can autotomise (voluntarily shed) a damaged leg to prevent further harm. Lost legs can regenerate to some degree over subsequent moults in juveniles, though regenerated legs are often smaller than the originals. Adults don't moult again, so a lost leg in an adult spider is permanent.
Prevention: always handle over a low, soft surface. A table with a cloth on it, a bed, or a carpeted floor directly beneath you. Don't handle standing up. Don't handle near edges.
Parasitic mites
Grain mites (Acarus siro) occasionally turn up in jumping spider enclosures. They appear as tiny white or translucent dots moving around on surfaces, particularly near food sources. They're not parasites of the spider itself, but they indicate excess moisture and overfeeding, which are problems in their own right.
Parasitic mites that actually attach to the spider are less common in jumping spiders than in some other arachnids. If you see tiny dots physically attached to your spider's body, that's a different problem. Reduce humidity, improve ventilation, clean the enclosure thoroughly, and rehouse the spider into a fresh setup. There are no safe acaricides for use on jumping spiders.
Refusal to eat
A spider that won't eat is almost always either in pre-moult or has recently moulted. This is normal and not a health problem. Pre-moult fasting can last anywhere from a few days to several weeks. Leave the spider alone, remove uneaten prey, and wait.
If a spider refuses food for an extended period without any signs of moulting (no darkened abdomen, no thickened retreat sac, no recent moult), consider:
- Temperature. Is it warm enough? Cold spiders don't eat.
- Prey size. Is the prey too large and intimidating, or too small to trigger a hunting response?
- Stress. Has the enclosure been moved recently? Has there been a lot of handling? New spiders sometimes take a week or more to settle and start eating in a new environment.
- Old age. Elderly spiders eat less. If your adult female is past the 18-month mark and gradually reducing her food intake, that may simply be the natural decline.
When there's nothing you can do
Invertebrate medicine is limited. There are no antibiotics for spider infections and no surgery for internal problems. When a spider is visibly declining and you've ruled out the fixable problems (dehydration, temperature, mould, prey issues), sometimes the answer is that the animal is dying and you can't stop it.
This is harder to accept than it sounds, particularly with an animal that used to sit on your hand and tilt its head at you. But it's the reality of keeping small, short-lived animals. Good husbandry prevents most problems. For the rest, sometimes you just keep them comfortable and let nature take its course.