Tarantula Health: Molting, Feeding, and When to Worry

Tarantulas are among the most low-maintenance pets in the hobby, which is exactly why new keepers get into trouble. They do not need daily interaction, they can go weeks without food, and a healthy one may live for years while doing almost nothing visible. That calm is deceptive. Most tarantula deaths in captivity are not caused by disease; they are caused by well-meaning owners intervening at the wrong moment, keeping the wrong humidity, or panicking during a molt. Understanding the molt cycle and reading a tarantula's abdomen are the two skills that keep these animals alive for their full lifespan, which for a female of some New World species can stretch past 20 years.

The Molt Cycle: The Most Critical Phase

A tarantula grows by shedding its entire exoskeleton, a process called molting. It is the most vulnerable and most misunderstood period in the animal's life. Molting happens more often in fast-growing spiderlings, every few weeks to a couple of months, and slows to once or twice a year in adults. Recognizing the approach of a molt, known as premolt, tells you when to stop feeding and leave the animal alone.

The signs of premolt are consistent. The tarantula refuses food for days or often weeks. A bald patch on the top of the abdomen darkens noticeably as the new exoskeleton forms beneath. The whole animal often looks duller and darker, sometimes with a bluish sheen to the leg joints. It becomes lethargic, hides, webs up its burrow, and eventually flips onto its back or side to molt. A tarantula lying upside down is not dead; it is doing the most important thing it will do all year.

The single most important rule in tarantula keeping is this: never disturb a molting tarantula. The fresh exoskeleton emerges soft and pliable, and the animal is essentially helpless until it hardens. Interference, whether trying to help remove skin or simply moving the enclosure, is one of the most common ways keepers kill an otherwise healthy spider. Patience is the entire skill here.

Feeding, Hydration, and Reading the Abdomen

Feeding a tarantula is simple. Offer appropriately sized prey, typically a feeder insect no larger than the spider's body length, and adjust frequency to the animal's stage: spiderlings eat every few days, adults often only once every week or two. Always remove uneaten prey within 24 hours so it cannot harass the spider, and never feed during premolt or the soft post-molt window.

Hydration is where the abdomen becomes your gauge. A healthy, well-hydrated tarantula carries a plump, rounded abdomen. As it dehydrates, that abdomen shrivels, wrinkles, and looks shrunken relative to the body. The most alarming sign is the "death curl," a tucked posture with the legs pulled tightly underneath the body, which signals severe dehydration or systemic decline and is an emergency. The best defense is boringly simple: keep a shallow dish of clean water available at all times, even for desert species, and never rely on misting alone to hydrate an animal.

Substrate Moisture and Fall Risk by Species Type

There is no single correct humidity for tarantulas, because the hobby spans arid desert species and humid rainforest species. Getting this wrong is a leading cause of chronic health problems, so identify your exact species before you set up the enclosure. Arid and desert species, including many popular New World terrestrials, want mostly dry substrate with only a water dish for moisture; too much damp invites mold and mites. Tropical and rainforest species want a portion of the substrate kept lightly moist, usually by overflowing the water dish or dampening one corner. Too dry an enclosure for these species leads to failed molts and dehydration.

Enclosure design also protects against injury. Terrestrial tarantulas have heavy abdomens, and a fall from height can rupture that abdomen and kill the animal. For terrestrial species, keep the substrate deep and the vertical climbing space low, no more than about one and a half times the leg span from substrate to lid, so a fall is short. Arboreal species, by contrast, need height and vertical cork bark to climb. Matching the layout to the natural lifestyle keeps the spider both comfortable and safe.

Legality, Ethics, and Finding Help Before You Need It

Tarantulas are widely legal to keep, but rules vary by state, country, and sometimes city, and some species face import or ownership restrictions. Old World species in particular carry more potent venom and defensive temperaments, and they are not beginner animals; an impulse purchase of a fast, defensive Old World tarantula is how people end up with a painful bite or a dead spider. Research the specific species, its adult size, its temperament, and your local laws before acquiring one, and buy from reputable breeders rather than on a whim.

Few general vets treat invertebrates, so identify an exotics vet or an experienced local keeper community before an emergency, because when something goes wrong you will want that contact already in hand. Keeping a written record of molts, feedings, refusals, and abdomen condition turns a hard-to-read animal into a legible one. VetGPT gives invertebrate keepers photo-based analysis, feeding and molt logs, and reminders in one place, alongside exotic pet care tracking built for the dozens of unusual species people keep. That history is what lets you tell the difference between a normal fast and a real problem.

Common Questions

How do I know my tarantula is about to molt?

Premolt signs include refusing food for days or weeks, a darkening bald patch on the abdomen, a duller darker color, lethargy and hiding, webbing up, and eventually flipping onto its back. A tarantula on its back is molting, not dead. Stop feeding, keep water available, and leave it undisturbed.

Should I ever help or disturb a molting tarantula?

No. Never touch, move, feed, or help pull skin off a molting tarantula. The new exoskeleton is soft and fragile, and a molt can take an hour to over a day. Interfering is a leading cause of keeper-caused death. Remove live feeders, keep it quiet, and wait 1 to 2 weeks for the fangs to harden before feeding.

How can I tell if my tarantula is dehydrated?

A hydrated tarantula has a plump, rounded abdomen. A shriveled or deflated abdomen signals dehydration, and a tucked death curl is an emergency. Always keep a shallow water dish full, even for desert species; a constant water source is the safest prevention.

How moist should the substrate be?

It depends on the species. Arid and desert species want mostly dry substrate with a water dish. Tropical species want part of the substrate kept lightly damp. Research your exact species, because too damp invites mold and mites while too dry causes failed molts and dehydration.