Growth Stages

Understanding growth stages is one of the most practical things you can learn as an invertebrate breeder because it shapes every decision you make from the moment offspring appear until they reach maturity. How you house, feed, and manage young animals changes dramatically depending on where they are in their development, and getting this wrong at critical stages can cost you animals that were otherwise healthy and thriving. Whether you are raising tarantula slings, mantis nymphs, beetle larvae, or shrimp fry, knowing what to expect at each phase and what your animals need to get through it successfully is the foundation of raising offspring well.

This applies to every breeder who is raising young invertebrates, regardless of species. The specifics vary enormously -- a tarantula sling's growth trajectory looks nothing like a millipede's larval development, and neither resembles the rapid molting schedule of a young mantis nymph. But the general principle is universal: invertebrates grow in defined stages punctuated by molts, and each stage brings different requirements for space, food, humidity, and management. Understanding this framework lets you anticipate what your animals need before problems develop rather than reacting after something goes wrong.

Growth stages matter to breeders specifically because the early stages are where you lose the most animals. Mortality is highest in the youngest age classes across nearly every invertebrate group, and much of that loss is preventable with proper husbandry matched to developmental needs. A sling that desiccates because humidity was too low, or a nymph that fails to molt because it lacked adequate space, represents a failure of management rather than an unavoidable loss. The better you understand what each stage demands, the more offspring you bring through to healthy adulthood.

New breeders frequently ask how fast their animals will grow and when they will be ready to sell or breed. The honest answer is that growth rates vary tremendously depending on species, temperature, feeding frequency, and individual genetics. What you can predict with reasonable accuracy is the sequence of stages your animals will pass through and what conditions support successful transitions between them. That predictability gives you a management framework even when exact timelines remain uncertain.

This article covers the biological basis of invertebrate growth, how growth stages differ across major groups, practical guidance for supporting each developmental phase, and the common mistakes that cost breeders animals during the vulnerable early stages.

Invertebrate growth is fundamentally different from vertebrate growth because it occurs through molting. The rigid exoskeleton that protects an invertebrate also constrains its size, so growth requires periodically shedding the old exoskeleton and forming a new, larger one. Each interval between molts is called an instar, and an animal progresses through a species-specific number of instars before reaching its adult size. The molting process itself is one of the most dangerous periods in an invertebrate's life, requiring precise conditions and leaving the animal temporarily soft and vulnerable.

The earliest instars are where growth is most rapid and mortality is highest. Newly hatched or newly emerged young are tiny, fragile, and highly sensitive to environmental conditions. They dehydrate quickly, they are vulnerable to predation including from siblings in some species, and they require food sources appropriately scaled to their size. The combination of high vulnerability and rapid development makes the first few instars the period where your husbandry matters most. Getting conditions right during this window determines what percentage of your brood survives to the intermediate stages where they become much hardier.

Intermediate instars represent the growth phase where animals are past their most vulnerable period but still developing toward maturity. During these stages, growth often slows somewhat compared to the explosive early development, and the animals become progressively more robust and tolerant of minor environmental variations. This is typically when breeders have the most flexibility in housing and feeding management, and when animals can be safely rehoused into individual enclosures or moved to grow-out setups that accommodate their increasing size. The intermediate phase is also when sex determination becomes possible in many species, which matters for planning future pairings.

The approach to sexual maturity marks a critical transition that breeders need to recognize and manage differently than earlier growth. Animals nearing their final molts may require different temperature regimes, feeding schedules, or housing arrangements to successfully complete maturation. In some species, males and females mature at different rates, with males often reaching adulthood sooner and having shorter adult lifespans. Recognizing when animals are approaching maturity allows you to plan pairings, separate sexes if needed, and adjust husbandry to support the final developmental transition.

Molting success depends on several environmental factors that breeders must provide consistently. Adequate humidity is critical for most terrestrial species because the new exoskeleton needs moisture to expand properly before it hardens. Sufficient space allows the animal to position itself and extract from the old exoskeleton without physical obstruction. Appropriate substrate depth matters for burrowing species that molt underground. Freedom from disturbance during and immediately after molting prevents interrupted molts that can be fatal. These requirements are non-negotiable during active molting periods and must be maintained throughout the growth phases.

The total time from hatching to maturity varies from weeks in some fast-growing insects to years in slow-developing arachnids and myriapods. This timeline has direct implications for breeding program management, including how long you need to house and feed growing animals, when offspring will be ready for sale or trade, and how quickly you can cycle through generations for genetic management purposes. Realistic expectations about growth timelines prevent frustration and help you plan the resources needed to raise offspring responsibly.

Arachnid growth stages are characterized by relatively slow development and dramatic size differences between early and late instars. Tarantula slings emerge from the egg sac as tiny first or second instar animals that may take three to ten years to reach maturity depending on the species and sex. Each molt represents a visible size increase, and breeders often track progress by instar number. Males typically mature faster than females and have fewer total instars, which affects breeding program timing. Scorpion growth follows a similar pattern with young riding on the mother's back through the first instar before dispersing. Scorpion instars are generally numbered one through six or seven, with maturity reached after the final molt.

Insect growth stages show enormous variation across orders. Mantis nymphs progress through a defined number of instars, typically six to nine depending on species and sex, growing rapidly enough that some species reach adulthood within a few months. Beetle larvae are the grub-like larval stage that bears no resemblance to the adult form, spending months or years feeding and growing underground before pupating and emerging as adults. This complete metamorphosis means beetle breeders manage two fundamentally different life stages with completely different care requirements. Stick insects and roaches develop through gradual metamorphosis where nymphs resemble small adults and grow progressively larger through each instar.

Myriapod growth is distinctive because many species continue adding body segments as they grow, unlike most other arthropods that hatch with their full complement of segments. Millipede larvae called stadium stages begin with fewer legs and segments than adults and gradually add more with each molt. This process can take several years for large species, making millipede rearing a long-term commitment. Centipedes either hatch with their full number of leg pairs or add segments progressively depending on the order, with growth to maturity taking months to years depending on species and conditions.

Crustacean and mollusk growth stages differ significantly from terrestrial arthropods. Shrimp pass through larval stages that may require different water conditions than adults, though many freshwater species commonly bred in the hobby produce miniature versions of the adults that can be raised in the same tank. Isopods give birth to mancae that emerge from the marsupium as small but fully formed juveniles, growing through successive molts within the colony. Snail growth is continuous rather than stage-based, with the shell growing incrementally as the animal feeds and develops. Each of these groups requires growth management strategies tailored to their specific biology rather than borrowed from arthropod care guides.

The universal lesson across all invertebrate groups is that growth is not linear or continuous -- it happens in discrete jumps separated by molts, and each transition point represents both a vulnerability and an opportunity. Understanding where your animals are in this process informs every husbandry decision you make during the rearing period.

Set up rearing enclosures before offspring arrive rather than scrambling to house them after they emerge. For individually housed species like tarantula slings, this means having appropriately sized small containers with ventilation, substrate, and water sources ready in advance. For colonial species, prepare a grow-out enclosure with conditions matched to the needs of the youngest animals, which often means higher humidity and smaller food items than adult enclosures provide. Having everything ready eliminates the stressful gap between offspring appearing and having proper housing available.

Match food size to animal size at every stage. One of the most common causes of failure in rearing young invertebrates is offering prey or food items that are too large for the animals to handle. Newly emerged slings, nymphs, and juveniles need food scaled to their body size -- fruit flies for tiny mantis nymphs, pre-killed pinhead crickets for small tarantula slings, powdered or finely ground food for millipede larvae. As animals grow through successive instars, increase food size proportionally. Feeding appropriate food at each stage supports steady growth and reduces the stress of failed feeding attempts.

Monitor humidity carefully during the early instars when animals are most vulnerable to desiccation. Small invertebrates have a high surface-area-to-volume ratio that makes them lose moisture rapidly, and many early instar deaths are attributable to insufficient humidity rather than disease or genetic problems. This does not mean keeping enclosures soaking wet, which causes its own problems. It means maintaining appropriate moisture levels through substrate choices, ventilation adjustments, and regular misting schedules tailored to the species you are raising. Observe your animals and adjust based on their behavior rather than relying solely on instrument readings.

Track growth progress to identify problems early. Note molt dates, premolt behaviors, and any failed molts for individually housed animals. For colonies, observe the general size distribution and look for signs that growth is progressing normally across the population. Animals that stop growing, skip feeding for extended periods outside of normal premolt fasting, or repeatedly fail to complete molts may be experiencing environmental problems that need correction. Early identification of stalled growth gives you time to adjust conditions before you lose the animal.

Plan the transition from rearing to permanent housing or sale as animals reach appropriate size. Keeping animals in rearing containers too long creates crowding stress and can delay development, while moving them too early into adult-sized enclosures makes monitoring and feeding more difficult. Most breeders find that animals can be safely moved to larger enclosures or sold once they have completed several molts, gained enough size to be robust, and are feeding consistently. This is also the stage where separating animals by sex becomes important for species where you need to prevent premature or unwanted breeding.

The most frequent mistake in managing growth stages is applying a one-size-fits-all approach to housing and care across all instars. The conditions that work perfectly for a subadult tarantula can be lethal for a first instar sling from the same species. Young animals need smaller enclosures, higher humidity, smaller food, and more frequent monitoring than older ones. Treating every growth stage the same way because it simplifies management leads to preventable losses in the earliest and most vulnerable instars where the margin for error is thinnest.

Disturbing animals during the molting process is a mistake that costs more animals than most keepers realize. Molting invertebrates need to be left completely alone. Opening enclosures to check on them, moving containers, introducing food during active molting, or having vibrations from nearby activity can all interrupt the process with fatal consequences. Learn to recognize premolt signs for your species -- reduced feeding, color changes, positioning on substrate -- and leave the animal undisturbed from the moment premolt behavior begins until the new exoskeleton has hardened, which can take hours to days depending on the species and size.

Underestimating the time and resources required to raise large numbers of offspring to sellable size leads many breeders into difficult situations. A mantis ootheca might produce a hundred nymphs, a tarantula sac might yield three hundred slings, and an isopod colony might suddenly boom with hundreds of mancae. Each of those animals needs housing, feeding, and monitoring through multiple growth stages. Breeders who plan for the excitement of hatching but not for the months of daily care that follow find themselves overwhelmed, and the animals suffer when resources are stretched too thin. Realistic planning based on actual numbers and growth timelines prevents this problem.

Feeding inappropriate food during critical growth periods stunts development and increases mortality. Offering prey that is too large frustrates young animals and can even injure them. Offering food that lacks proper nutrition, like only one type of feeder insect for months at a time, produces animals that grow slowly and molt poorly. Varied, appropriately sized nutrition at each growth stage is an investment that pays off in faster development, better survival rates, and healthier adults that are more attractive to buyers and more suitable for future breeding.

Ignoring species-specific growth requirements because general care guides are easier to follow than targeted research is a recurring problem. A care sheet written for one tarantula species may not accurately reflect the growth rate, humidity needs, or feeding schedule of a different species with very different natural history. Growth stage management requires understanding your specific animal's biology, not just the broad category it belongs to. The time spent researching the particular needs of your species before offspring arrive is always less than the time spent trying to save animals that are failing because conditions were wrong from the start.

Growth stages define the developmental roadmap that every invertebrate follows from emergence to maturity, and understanding this roadmap is essential for raising healthy offspring. Each stage brings specific requirements for housing, humidity, food size, and disturbance levels that differ from the stages before and after it. The breeders who succeed in rearing high percentages of their offspring to healthy adulthood are the ones who anticipate these changing needs and adjust their management accordingly rather than waiting for problems to force their hand.

The early instars deserve your most careful attention because that is where the greatest losses occur and where your husbandry has the most impact. Small animals are fragile, dehydrate easily, and require food and conditions precisely matched to their size. Investing extra care during the first weeks and months of development pays off disproportionately in survival rates and in the quality of the animals that make it through to the more forgiving intermediate stages.

Every invertebrate group handles growth differently, and the specifics of your species matter more than general guidelines. A tarantula sling's growth trajectory spans years. A mantis nymph might reach adulthood in months. A beetle larva undergoes complete metamorphosis that transforms it into a fundamentally different creature. Learning the particular growth pattern and stage-specific needs of the species you are breeding is not optional -- it is the foundation of competent rearing practice.

Approach the rearing period as a commitment that extends well beyond the excitement of a successful hatch. The real work of breeding is not producing offspring but raising them through every growth stage with the care and resources they need to become strong, healthy adults. Planning for this commitment before you breed, and following through on it consistently, is what separates responsible breeders from keepers who simply produce animals they are not prepared to raise.