What actually happens when you raise spiders from egg to adult
Most people who get into keeping spiders think it's just feeding something occasionally and waiting. It's not that simple. The Life Stages Of A Spider each have different requirements, and getting one part wrong usually means you lose the specimen before it matures. I spent years working with arachnids in a lab setting before moving into private study, and the difference between a successful colony and a pile of dead shells mostly comes down to understanding what each stage actually needs rather than following generic care sheets. Spiders go through four distinct phases: egg, spiderling, juvenile (multiple instars), and adult. The egg stage is where most beginners fail because they don't understand that egg sacs require very specific humidity levels or the eggs just desiccate or mold out. A typical orb-weaver egg sac needs somewhere between 70 and 85 percent relative humidity. Below 65 percent, the membranes dry out and the embryos die. Above 90 percent, Aspergillus and other molds take over within 48 hours. I keep a simple hygrometer next to every enclosure and check it twice daily. That's the baseline. The spiderling stage is the next filter. Newly hatched spiders are essentially miniature versions of adults, but their water retention is terrible compared to later stages. They desiccate faster than you'd expect. I once lost an entire clutch of jumping spider spiderlings because I was using coconut coir as substrate, which holds moisture too aggressively at the bottom while the top layer stays dry. The babies would crawl down looking for humidity and drown in the saturated zone. Switching to a thin layer of paper towels with a slightly damp corner fixed the problem entirely. The key insight nobody tells you is that spiderling enclosures should feel dry to the touch on the surface but have a hidden moisture zone they can access, not the other way around.
Molting and the instar system
Spiders grow by molting, and each molt represents a new instar. A tarantula might go through 6 to 12 instars before reaching sexual maturity. Some wolf spider species can molt 20 or more times. Each molt is a vulnerability window where the new exoskeleton is soft for anywhere from a few hours to several days depending on species and temperature. During this time, the spider cannot defend itself and should not be fed. I've seen people post on forums about spiders that died after being offered food during a molt and the stress of the encounter caused complications. Don't feed during molts. Just leave them alone. Temperature controls molt frequency significantly. Higher temperatures speed up metabolism and generally shorten the interval between molts, but pushing it too far creates weak exoskeletons. The sweet spot for most temperate species is around 24 to 27 degrees Celsius. Tropical species can handle higher, but exceeding 30 degrees regularly leads to chronic stress and abnormal molts. I track molt intervals in a spreadsheet and noticed that my Mexican redknee tarantula went 14 months between its fifth and sixth instar at 24 degrees, then only 9 months when I bumped the enclosure to 27 degrees. The tradeoff is that the newer exoskeleton at the higher temperature was noticeably softer and more prone to damage during handling.
Sexual maturity and the final molt
The transition from juvenile to adult is marked by the final molt, which in males often involves dramatic changes. Mature male tarantulas develop palp bulbs and sometimes tufts of hair on their legs for sperm transfer. Females tend to look more or less the same across their final molt, just larger and with a more developed epigyne. This is why sexing many spider species requires the animal to be fully mature, which can take years for larger tarantulas. Some people try to sex juveniles by looking at abdominal patterns, but that's unreliable except in a handful of species where the pattern is distinctly different between sexes from early instars. Here's a counter-intuitive point: males often stop eating before they reach sexual maturity. They enter what's called a pre-adult wander phase where they're motivated to find a mate rather than feed. If you're keeping a male and he stops eating, don't immediately assume health issues. Check whether he's showing other signs of maturity like leg tufts or palp swelling. In my experience, a healthy male that's about to molt into adulthood will lose interest in food for 2 to 4 weeks prior. Force-feeding during this period just stresses him more.
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Common pitfalls in practice
The biggest mistake I see is people treating all spiders the same way regardless of life stage. A mature tarantula and a spiderling of the same species have completely different enclosure requirements, feeding schedules, and humidity needs. Using a large enclosure with a single water dish for spiderlings is a death sentence. The spiderlings will either drown or fail to catch prey because the feeder insects are too large and active. Partition the enclosure or use a separate small container for spiderlings. Another issue is overfeeding adults. Spiders can go weeks without eating, and leaving excess food in the enclosure attracts mites and fruit flies. I clean out uneaten prey within 24 hours for most species. Larger tarantulas can handle a longer window, but even then, I usually remove anything left after 48 hours. Mite infestations are the number one reason I see kept spiders decline. They start small and invisible, then devastate the animal by feeding on its hemolymph. Regular enclosure cleaning and quarantining new specimens for at least two weeks before adding them to an existing collection are non-negotiable. The Life Stages Of A Spider are straightforward in theory but demand specific attention at each phase. There's no universal shortcut. The spiders that survive longest in captivity are the ones where someone actually understands what's happening at each stage and adjusts accordingly rather than following a one-size-fits-all routine.
