Egg case: about 16 eggs, hatching in 42 days at 29.5 °C to 81 days at 21 °C (UF/IFAS; Ebeling). Nymphs: 7–10 moults over about a year (UF/IFAS; Penn State). Adults: 34–180 days (UF/IFAS); females 34–181, males 112–160 (Ebeling). Season: adults peak in late spring and early summer (Penn State).
Oriental cockroach life cycle
The oriental cockroach life cycle is slow and seasonal. A female drops an egg case of about 16 eggs; it hatches after 42 to 81 days; the nymphs then take about a year — often longer — to become adults; and the adults live a few months, mostly in late spring and summer (UF/IFAS; Ebeling; Penn State). Unlike the German cockroach, which breeds non-stop in warm kitchens, the Oriental cockroach "generally has a seasonal developmental cycle" (Penn State).
- Egg case (ootheca). About 10 × 5 mm, "reddish brown and soft" when new, then "black, hard, and brittle" (Ebeling). Each holds about 16 eggs in two rows (UF/IFAS). The female carries it for 12 hours to five days — about 30 hours on average (UF/IFAS; Penn State) — then drops it or attaches it to debris in a sheltered spot near food.
- Nymphs. Newly hatched nymphs are about 6 mm long (Ebeling), larger than German or American hatchlings. They moult seven to ten times (UF/IFAS; Penn State) over about a year (UF/IFAS); at room temperature Ebeling gives 515 days for males and 542 for females.
- Adults. Males have wings covering about three-quarters of the abdomen; females have only short wing pads. Neither sex can fly (UF/IFAS). A female produces about eight egg cases in her life (UF/IFAS).
At 22 °C (71.6 °F), typical of a basement, the shared model gives an egg case of about 76 days and nymphs of about 529 days, so about 605 days from egg case to adult. UF/IFAS's gallery gives the overall range as 200 to 800 days, and 575 to 600 days "under average conditions".
How warmth changes each stage
Both the egg case and the nymphs have been timed at more than one temperature, so this species' calculator adjusts both. Egg cases took 81 days at 21 °C and 42 days at 29.5 °C (Ebeling; UF/IFAS); nymphs took 515–542 days at room temperature but only 288–310 days at 27.8 °C (Ebeling).
| Temperature | Egg case | Nymphs: male / female | Egg case to adult |
|---|---|---|---|
| 20 °C (68 °F) | 81 days | 515 days / 542 days | 19.6–20.5 months (up to 1.7 years) * |
| 21 °C (69.8 °F) | 81 days | 515 days / 542 days | 19.6–20.5 months (up to 1.7 years) * |
| 22 °C (71.6 °F) | 76 days | 515 days / 542 days | 19.4–20.3 months (up to 1.7 years) * |
| 24.4 °C (75.9 °F) | 65 days | 515 days / 542 days | 19.1–20 months (up to 1.7 years) |
| 26 °C (78.8 °F) | 58 days | 408 days / 433 days | 15.3–16.1 months (up to 1.3 years) |
| 27.8 °C (82 °F) | 50 days | 288 days / 310 days | 11.1–11.8 months |
| 29.5 °C (85.1 °F) | 42 days | 288 days / 310 days | 10.8–11.6 months * |
* At least one part (egg case or nymphs) is outside the measured temperatures, so the nearest measured value is used for it. Ebeling's "room temperature" nymph figures are placed at 24.4 °C (76 °F), the temperature he gives for Gould and Deay's cultures.
Oriental cockroach lifespan
The oriental cockroach lifespan is mostly nymph time. Adults are short-lived: "An adult Blatta orientalis can live from 34 to 180 days" (UF/IFAS); the UF/IFAS gallery says 160 to 180 days; Penn State gives 5 to 26 weeks for females. Ebeling's rearing records split it by sex — females 34–181 days and males 112–160 days — though from only five females and four males.
| Who | Adult lifespan | Total from the egg |
|---|---|---|
| Female | 1.1–5.9 months | 21.4–26.3 months (up to 2.2 years) |
| Male | 3.7–5.3 months | 23.1–24.7 months (up to 2.1 years) |
| Not sure | 1.1–5.9 months | 20.5–26.3 months (up to 2.2 years) |
Counting from the egg case, then, an Oriental cockroach in a 22 °C building lives about 1.7–2.2 years. Water limits it more than food: Penn State says adults can last a month without food if they can drink, but die within two weeks without water. For any species, sex and temperature, the cockroach lifespan calculator gives the same numbers as this page.
Oriental cockroach nymphs and adults
Oriental cockroaches look more alike across their life than most species, because even the adults have short wings. The differences are size, wing length and colour:
| Stage | Size | What it looks like | How long |
|---|---|---|---|
| Egg case | 10 × 5 mm; about 16 eggs | reddish brown and soft, then black, hard and brittle | 42–81 days (UF/IFAS) |
| Young nymph | about 6 mm when newly hatched | shiny reddish brown, no wings | first months |
| Older nymph | up to adult size | dark reddish brown to black, no wings | about a year in total; 7–10 moults |
| Adult male | about 25 mm (1 in) | shiny black; wings cover about ¾ of the abdomen | 112–160 days (Ebeling) |
| Adult female | about 32 mm (1¼ in) | broader; only small wing pads | 34–181 days (Ebeling) |
Sources: Ebeling (egg case, first-instar size, adult lifespans), UF/IFAS gallery (adult sizes, nymph colours), UF/IFAS EENY-159 and Penn State (wings, moults). UF/IFAS EENY-159 gives 22–27 mm for adults in general.
Oriental cockroach nymph
An oriental cockroach nymph is easy to mistake for a small adult female, because neither has full wings. "Early nymphs are a shiny reddish-brown in color, while older instars are dark reddish-brown to black" (UF/IFAS gallery). Look for the female's small wing pads just behind the shield: nymphs don't have them. Because nymphs take about a year to mature and adults appear mainly in late spring, a basement full of dark, wingless roaches in autumn or winter is usually last summer's young growing up.
Oriental cockroach vs American cockroach
The oriental cockroach vs american cockroach pair often turn up in the same places — basements, crawl spaces and drains — and both have been called water bugs. They're easy to tell apart:
| Oriental cockroach | American cockroach | |
|---|---|---|
| Size | 22–32 mm (about 1–1¼ in) | 34–54 mm (1⅜–2⅛ in) |
| Colour | shiny black to very dark brown, no markings | reddish brown with a pale band around the shield |
| Wings | short (males ¾ of abdomen, females pads); can't fly | long; both sexes can fly |
| Egg case | 10 × 5 mm, about 16 eggs, hatches in 42–81 days | 8 × 5 mm, 14–16 eggs, hatches in 31.8–57.4 days |
| Egg to adult | about a year to two years | about 600 days on average |
| Adult life | 34–181 days | 90–706 days (females) |
| Climate | cool, damp places; survives freezing weather outside | warm, damp places; heated buildings in the North |
Sources: UF/IFAS, Ebeling, Penn State, Texas A&M. For the American cockroach's lifespan by sex and its dated life cycle, see the American cockroach lifespan calculator.
Why Oriental cockroaches are called "water bugs"
UF/IFAS explains that it is "sometimes referred to as the 'black beetle' or a 'water bug' because of its dark black appearance and tendency to harbor in damp locations". Penn State says the same: they're often called water bugs "because of their preference for dark, damp, and cool areas". If someone calls a water bug cockroach a black beetle, they mean this species — though it is a cockroach, not a beetle and not a true water bug.
The habitat list explains the name. UF/IFAS finds them in "basements, crawl spaces, areas between the soil and foundation, underneath sidewalks, in sewer pipes, in floor drains, and under sinks or any other damp, cool area in the house", and outdoors they "sometimes aggregate near or under garbage cans". Penn State adds abandoned cisterns, water-valve pits and leaf litter. They rest on damp surfaces so consistently that insecticide residues there break down quickly (UF/IFAS) — one reason extension guides start with moisture instead: fix plumbing leaks, ventilate damp spaces and keep drain traps full or capped (UF/IFAS).
The "water bug" label is old and loose. Purdue's Gould and Deay noted in 1938 that German, American and Oriental cockroaches had all been called water bugs, "because of their frequent occurrence around sinks and water pipes". For how long any cockroach can last underwater or without air, see how long a cockroach can live underwater.
Oriental cockroach season: seasonal patterns
This is the one common pest cockroach with a clear oriental cockroach season. "The species tends to be seasonal, with adults appearing in spring and summer" (UF/IFAS). Penn State is more specific: "The peak number of adults usually appears in late spring or early summer. By late summer and early fall, this number has become quite low." Older rearing records put adults "appearing in May and June and dying during July" (Gould and Deay 1940; Rau 1924, quoted by Ebeling). Pairing, though, "takes place at any season" (UF/IFAS).
| Month | Northern Hemisphere | Southern Hemisphere |
|---|---|---|
| January | Few adults | Adults dying off |
| February | Few adults | Adult numbers low |
| March | Few adults | Adult numbers low |
| April | Adults starting to appear | Adult numbers low |
| May | Peak season for adults | Few adults |
| June | Peak season for adults | Few adults |
| July | Adults dying off | Few adults |
| August | Adult numbers low | Few adults |
| September | Adult numbers low | Few adults |
| October | Adult numbers low | Adults starting to appear |
| November | Few adults | Peak season for adults |
| December | Few adults | Peak season for adults |
Winter isn't described in the sources we read, so those months are marked "Few adults": the population is mostly last summer's nymphs, still growing. The Southern Hemisphere column is our assumption — the same pattern six months later — because all of the studies come from the United States. Cold doesn't wipe them out: UF/IFAS notes this species "can also survive outside in freezing weather", and it "will often seek refuge indoors when a drop in temperature occurs" (UF/IFAS EENY-159). Dry spells push them indoors too, "apparently in search of higher humidity" (Penn State).
How this calculator works
The calculator uses the shared cockroach data model, so its Oriental cockroach numbers match the general cockroach life cycle calculator and the lifespan calculator exactly.
- Egg case: straight-line interpolation between 81 days at 21 °C and 42 days at 29.5 °C (Ebeling; UF/IFAS), held at the nearest measured value outside that range.
- Nymphs: male and female times at "room temperature" (515 and 542 days, placed at 24.4 °C) and at 27.8 °C (288 and 310 days), interpolated between and held outside; the timeline uses the average of the two sexes (Ebeling).
- Dates: counted from the day the egg case was dropped, if you enter one.
- Seasonal note: a month-by-month status from UF/IFAS, Penn State and Ebeling's sources. Southern Hemisphere months are shifted by six months, which is our assumption.
Development data come from small laboratory samples; real basements vary in temperature through the year, which stretches development further.
Frequently asked questions
What is the Oriental cockroach life cycle?
Egg case (about 16 eggs, hatching in 42–81 days), nymphs (7–10 moults over about a year) and short-lived adults (UF/IFAS; Penn State).
How long do Oriental cockroaches live?
Adults live 34–180 days (UF/IFAS); with about a year or more as a nymph first, the whole life is roughly a year and a half to two years.
How long does an Oriental cockroach egg case take to hatch?
About 42 days at 29.5 °C to 81 days at 21 °C, and about two months at normal room temperature (Ebeling; UF/IFAS).
What does an Oriental cockroach nymph look like?
Wingless; shiny reddish brown when young, dark reddish brown to black when older (UF/IFAS).
Can Oriental cockroaches fly?
No. Males have wings covering about three-quarters of the abdomen and females only small pads, and both are flightless (UF/IFAS).
Why is the Oriental cockroach called a water bug?
Because it is dark and lives in damp places such as basements, drains and crawl spaces (UF/IFAS; Penn State).
When is Oriental cockroach season?
Adults peak in late spring and early summer and are few by late summer and early fall (Penn State); older records put adults in May and June, dying in July (Ebeling).
How do I tell an Oriental cockroach from an American cockroach?
The Oriental is shiny black with short wings and can't fly; the American is larger, reddish brown, long-winged and can fly. See the American cockroach page.
Do Oriental cockroaches survive winter?
Yes. They can survive outside in freezing weather (UF/IFAS) and move indoors when temperatures drop (UF/IFAS EENY-159).
How many eggs does an Oriental cockroach lay?
About eight egg cases of about 16 eggs each in her life (UF/IFAS).
These calculators give estimates from laboratory, extension and husbandry figures, for education. Real cockroaches vary with strain, food, humidity and temperature. Cockroach droppings, saliva and shed skins contain allergens that can trigger asthma, especially in children (CDC; Penn State) — for health questions, talk to a doctor. For a heavy infestation, contact a licensed pest professional or your local extension service. We name no products and give no pesticide doses.