Discoid Roach Nymph Instars Explained: From Hatch to Adult

What Is an Instar?

An instar is the stage of a roach's life between molts. The first instar is the period from hatching until the first molt. The second instar is after the first molt until the second molt. And so on. Every time a roach molts, it moves into the next instar. Each molt is a discrete event—the roach emerges with a fresh exoskeleton, and its size and proportions change noticeably. The instar system is how entomologists (and keepers) track a roach's developmental progress from nymph to adult.

How Many Instars in Discoid Roaches?

Discoid roaches typically go through six to seven instars before reaching adulthood. The exact number can vary slightly depending on temperature, nutrition, and genetics, but six to seven is standard. A healthy discoid nymph from hatching to adult maturity passes through roughly seven molt events—seven times shedding the old exoskeleton to grow into a larger one.

After the seventh (or sometimes sixth) molt, the roach becomes a wingless adult. It stops molting. Its size stabilizes at its adult form. From that point on, it's all about reproduction and survival—no more growth.

Timeline: Temperature Dependent

The speed of development depends heavily on temperature. Discoid roaches develop fastest at around 85°F. At this temperature, the whole journey from hatch to adult might take about 4–5 months. As temperature drops, development slows. At 75°F, that same journey might take 6–7 months. Below 70°F, development slows significantly and might take 8+ months.

This has practical implications. If you're maintaining a feeder colony at a warm 85°F, your nymphs are reaching harvestable size faster, which means higher turnover and more feeders available in a given time. If your facility runs cooler, expect longer development times. This is something to account for when you're calculating how long it will take new roaches to grow to usable sizes.

First and Second Instars: The Tiny Stage

Newly hatched discoid nymphs are incredibly small—barely visible to the naked eye. A first instar roach is roughly the size of a gnat. They're barely of any value as feeders at this size; no reptile can consume them without difficulty.

In the first and second instars, nymphs are vulnerable and prone to escape. They can fit through tiny cracks. They're easy prey for larger roaches in the colony. They're also extremely delicate and sensitive to dehydration. If you're maintaining a colony with mixed ages, the first and second instar roaches are easy to overlook. They'll cluster in the dampest, most protected parts of the bin.

From a breeding perspective, this is the risky period. Nymphs that are protected from predation and kept in good conditions will progress normally. Neglected first-instars might die off en masse from dehydration or cannibalism.

Middle Instars: Third Through Fifth

By the third and fourth instars, discoid nymphs are starting to become visible and usable feeders for smaller reptiles. A third or fourth instar roach is roughly 1/4 to 3/8 inch long. These are appropriate for hatchling reptiles and are sometimes marketed as "small" roaches.

By the fifth instar, roaches are more substantial and clearly growing. They're about halfway to adult size. A fifth instar roach is in the "medium" size range and suitable for juvenile reptiles. At this stage, roaches are less delicate and more robust in their behavior. They're moving around more actively, feeding more aggressively, and molting with better reliability.

The middle instars are the bread-and-butter of a feeder colony's production. These are the sizes that most reptile keepers are buying and feeding most frequently. A colony producing strong, consistent fifth and sixth instar roaches is doing its job well.

Late Instars: Sixth and Seventh

The sixth instar is large and clearly nearing adulthood. A sixth instar roach is about 1/2 to 3/4 inch long. These are large feeders, appropriate for adult reptiles and growing juveniles. At this stage, roaches look almost fully adult in coloration and proportion—the only thing that's about to change is a final molt to wings and sexual maturity.

The seventh instar (or final nymphal stage) is indistinguishable from a mature roach in terms of feeding value. It's essentially adult-sized. After this last molt, the roach becomes a full adult and stops growing.

Late instars are the premium feeders—they're larger, packed with more nutrition, and ideal for adult reptiles. A discoid roach sold as "large" is usually a sixth or seventh instar, or a freshly molted adult that hasn't quite hardened into its final coloration.

Adult Stage: Maturity and Reproduction

After the final molt, a discoid roach is an adult. It's finished growing. Males develop small vestigial wings. Females develop a pronounced ovipositor. The roach's exoskeleton hardens and darkens to its final coloration—a deep brown or black. At this point, all the roach's energy goes into reproduction, not growth.

An adult discoid roach can live 1–2 years in good conditions. Females produce oothecae (egg cases) regularly if properly fed and housed. A single female might produce 20+ oothecae across her lifespan, each containing multiple nymphs. This is the engine of colony reproduction. As a keeper, you want your adult females healthy and well-nourished so they're productive.

Sizing and Marketing the Instars

Suppliers use different sizing conventions. "Small" roaches are typically third to fourth instars (1/4–3/8 inch). "Medium" roaches are usually fifth to sixth instars (3/8–3/4 inch). "Large" roaches are sixth-instar and adult roaches (3/4 inch and up). These sizes don't have a universal standard—one supplier's "medium" might be slightly different from another's. When buying, ask for size specifications in inches if you want to be precise about what you're getting.

Monitoring Colony Instar Distribution

A healthy, productive colony has roaches across all instars. You want newly hatched first-instars, robust middle instars, and plenty of breeding adults. A colony that's top-heavy with adults and short on young instars is headed for a crash—the adults are aging out, and there's not enough young stock replacing them. A colony with very few adults is also struggling because there's no one breeding.

Periodically scan your colony and do a rough instar census. How many obviously young roaches do you see? How many medium-sized ones? How many large adults? If the distribution is roughly balanced, you're doing well. If you see a concerning shortage of one category, adjust your management—feed more carefully to preserve young roaches, or adjust the colony to encourage breeding.

Temperature and Instars

Remember that temperature affects how fast roaches move through instars. A colony kept at 75°F will take about 20–25% longer to progress through each instar compared to a colony at 85°F. If you need roaches to reach a certain size quickly, warming the colony slightly will speed development. If you want to slow production (to reduce overcrowding), cooling the colony a bit will spread out the development timeline and buy you breathing room.

This is a useful tool for managing colony dynamics. It's also why understanding the instar system matters beyond just trivia—it directly affects your ability to predict when roaches will be ready and how many roaches you'll have at any given size.