Short answer. The carmine or "red" spider mite, Tetranychus cinnabarinus, is now usually treated as the red form of the twospotted spider mite, Tetranychus urticae [1]. Red and green mites interbreed, overlap in every body character used to separate them, and do not split in DNA studies [1]. For a cannabis grower the colour changes almost nothing. The same predators, set-points and acaricide rotation apply, and resistance follows a population's spray history, not its colour [1][11]. The full pest article is spider mites.
Red vs green form at a glance
| Feature | Green form (classic T. urticae) | Red form ("T. cinnabarinus", carmine mite) | Source |
|---|---|---|---|
| Active adult female colour | Yellowish-green to dark green, two dark side spots | Carmine red to dark red, dark spots | [1] |
| Male colour | Indistinguishable between forms | Indistinguishable | [1] |
| Larvae and nymphs | Pale, then green when feeding; never orange or red | Similar to green form | [1] |
| Eggs | Clear, translucent, becoming yellowish | Amber with a pink-reddish tint | [1] |
| Diapausing female | Bright orange, spots reduced or absent | Similar when diapause occurs | [1][7] |
| Dorsal skin lobes | Broader, rounded or oblong | Smaller, more triangular; overlaps | [1] |
| Typical climate | Cold temperate | Warm temperate, subtropical, greenhouses | [1] |
| True diapause | Usually yes (varies by population) | Often absent; present in some populations | [1] |
| Interbreeding | Produce viable hybrids with red form in many crosses | Same | [1] |
| Pesticide resistance difference | Not investigated | Not investigated | [1] |
| Recorded on hemp (extension) | Yes | Not reported separately | [8][9][10] |
Is the carmine mite a separate species from the twospotted spider mite?
The carmine mite is not a separate species in the view of most acarologists: Auger and colleagues concluded in 2013 that T. cinnabarinus should be treated as a synonym of the polymorphic species T. urticae, of which it is the red form [1]. Some authors still disagree.
Where the two names came from
The red mite was described by Boisduval in 1867, mainly by its colour [1]. Since then, about 44 species names have been synonymised with T. urticae, which shows how variable this mite is [1].
For decades, authors used colour, the shape of tiny lobes on the skin folds of the back, the shape of the male's aedeagus (copulatory organ), leg hairs, diapause and host plant to separate the two [1]. Each criterion has been used both to split and to lump them [1].
What the 2013 review found
Auger and colleagues found that every morphological character used to separate red and green mites varies within and between populations and overlaps with no clear cut-off [1]. The aedeagus, the key character for telling Tetranychus species apart, showed this most clearly [1].
They found no consistent link between body colour and the other characters [1]. Their own crosses between red and green populations, checked free of Wolbachia bacteria that can cause crossing failures, produced compatible offspring [1].
Phylogenetic studies based on the mitochondrial COI gene did not split mites by colour [1]. Instead, T. urticae falls into two major COI lineages that each contain red and green mites [1].
Why the debate is not closed
Molecular work partly revived the controversy: one 2009 study argued for the validity of T. cinnabarinus [1]. Auger and colleagues point out that many GenBank sequences labelled T. cinnabarinus are misidentified, which corrupts such analyses [1].
Crossing results are mixed. Several older studies found sterile or partly sterile hybrids between some red and green strains [1]. Gotoh and colleagues (1993) found partial compatibility between a non-diapausing red strain and green mites, but none between a diapausing red strain and the others [1]. Incompatibility between populations is common within spider mite species, so it does not by itself prove two species [1].
Label: synonymy is Supported (strong review, majority view); separate-species status is Contested. Chinese and some applied literature still reports "T. cinnabarinus" as a distinct pest [1].
How do you tell red and green spider mites apart on cannabis?
Red and green twospotted spider mites are told apart by the colour of active adult females under a 10-20x lens: carmine to dark red versus yellowish to dark green [1][7]. Colour is a clue, not a diagnosis.
Colour, and why it misleads
Spider mite colour comes mainly from carotenoid pigments and from the food in the gut, which shows as dark spots [1]. Both forms carry the same pigments in different amounts [1].
Colour darkens with age, shifts with diet, and fades or turns orange in diapausing and cold-exposed females [1]. Hybrids between red and green mites come in many shades: F1 females are pale red to dark red and never green, and later generations range from yellowish-green to bronze [1].
Males of the two forms cannot be told apart by colour [1]. Larvae and nymphs of both forms are pale to green and never orange or red [1].
Skin lobes and aedeagus
Under a compound microscope, the dorsal skin folds of green-form females carry broader, rounded lobes, and red-form females smaller, more triangular ones [1]. The two overlap.
Lobe density also changes with environment: green-form females reared at 35 °C and 15% RH had more lobes per 30 µm than those at 20 °C and 70% RH (Mollet and Sevacherian 1984, cited in [1]). Hibernating females of both forms have smooth folds without lobes [1].
The aedeagus shape varies within populations and overlaps between colour forms [1]. None of this is a field method.
Three look-alikes that are not carmine mites
- Diapausing twospotted females: bright orange-red, spots reduced or absent, not feeding, often hiding in cracks [7][8].
- Phytoseiulus persimilis: bright orange-red, pear-shaped, long-legged and fast, with no dark spots; eggs are larger and oval [7].
- Predatory midge larvae (Feltiella): orange, legless maggots in colonies [7].
Does red vs green matter for spider mite control?
Red vs green form makes no practical difference to cannabis spider mite control: the same predatory mites, environment set-points and acaricide rotation apply [1][7][13]. What matters is how resistant your population is, which depends on its spray history.
Pesticide resistance
Resistance has not been compared between the two colour forms [1]. Auger and colleagues note that existing data cannot tell whether resistance in a colour form comes from innate capacity or from different spray pressure [1].
The whole species evolves acaricide resistance quickly because of short generations, high fecundity and arrhenotoky (males from unfertilised eggs) [11]. Assume any mite on a clone from someone else's room is resistant to something. Rotate by IRAC group (6, 10A, 10B, 12, 13, 20, 21A, 23, 25; sulfur is UN) [13]. Follow the label and local law.
Heat tolerance
The red form is reported mostly from warm temperate and subtropical zones and from greenhouses in northern countries; the green form from cold temperate latitudes [1]. That hints at heat adaptation, but no direct comparison of upper thermal limits between the forms was found.
Cold tolerance differs more clearly. In field studies, hibernating green-form females were far more cold-resistant than red-form ones [1].
Diapause
Diapause is the trait that most often separated the forms, and it fails as a species marker [1]. Many red-form populations do not enter true diapause: they turn orange in autumn but resume feeding and red colour within days of warmth [1].
Yet diapause has been induced in red-form strains from Italy and Greece, the Greek strain at short days and 19 °C [1]. In Lebanon, red-form females diapause on mountains at 1,500 m but breed all year at lower altitude [1].
Diapause ability can be lost by tetranychid populations kept without winter [1]. Green-form diapause also varies with latitude [1]. One green-form strain had a critical photoperiod of about 13.5 h at 18 °C [12].
Cannabis implication. A 12/12 flower room is a short day. A strongly diapausing green-form population in a cool room may produce orange females that stop laying and hide; a red-form or long-indoor population may simply keep breeding. Either way, clean cracks and trays between runs (Supported, inferred, not tested on cannabis).
Host range
Red-form mites were long associated with carnation, which green mites were once thought unable to use [1]. Later work found green populations on carnation too, with success varying by cultivar [1]. Host adaptation varies between populations, not colours [1].
What are the life-table numbers for the red form?
One published life table for the red form ("T. cinnabarinus") on carnation leaves at 29.4 °C and 42% RH gave egg-to-adult development of 12.8 days, r_m of 0.183 per day and 3.9 eggs per female per day [3]. That is slower than green-form figures on cotton or apple, but host plant differs.
| Parameter | Red form, carnation, 29.4 °C, 42% RH [3] | Green form, cotton, 29.4 °C [2] | Green form, apple, 30 °C [4] |
|---|---|---|---|
| Egg-to-adult (days) | 12.84 | 6.1-6.7 (females, range across 3 species) | ~8.0 (computed from thermal constant) |
| Egg-to-adult survival | 80.2% | - | - |
| Female offspring | 76.3% | ~74% | - |
| Female longevity (days) | 24.3 | 9.7 | - |
| Eggs per female per day | 3.92 | - | - |
| Lifetime eggs | - | 64.3 | - |
| R0 (daughters/female) | 40.8 | - | 84.3 |
| Mean generation time (days) | 20.2 | - | - |
| r_m (/day) | 0.183 | ~0.29 | 0.302 |
| Doubling time (days, ln2/r_m) | 3.8 | ~2.4 | 2.3 |
Doubling times are computed here. No study has compared red and green forms on the same host at the same temperature that we could verify, and none on cannabis. Do not read the slower red-form numbers as "carmine mites are slower"; carnation is a different host and the authors used a different lab set-up [3].
What other Tetranychus spider mites could turn up on cannabis?
University hemp extension sheets from Utah, North Carolina and Colorado list only the twospotted spider mite as the spider mite pest of hemp [8][9][10]. We found no verified record of other Tetranychus species on cannabis.
Two western North American relatives are worth knowing because they feed on cotton and many other field crops near where outdoor hemp is grown:
- Strawberry spider mite, Tetranychus turkestani. UC IPM's degree-day model uses a lower threshold of 12.0 °C (53.6 °F), 112.1 DD (°C) egg-to-adult and 125.9 DD egg-to-egg on cotton [6].
- Pacific spider mite, Tetranychus pacificus. UC IPM's model uses a lower threshold of 11.1 °C (52.0 °F) and 121.0 DD (°C) egg-to-adult on cotton [5].
No published record of either on cannabis was found in the sources checked; treat them as possible outdoor visitors, not known cannabis pests. Telling them from T. urticae needs a slide-mounted male and a specialist.
Comparative life tables on cotton
Carey and Bradley reared all three species side by side on cotton cotyledons at 15.5 to 29.4 °C [2].
| Parameter | T. urticae | T. turkestani | T. pacificus | Conditions |
|---|---|---|---|---|
| Female egg-to-adult, 15.5 °C | 25.8-29.0 days (range across species) | same range | same range | [2] |
| Female egg-to-adult, 29.4 °C | 6.1-6.7 days (range across species) | same range | same range | [2] |
| Lifetime eggs, 23.8 °C | 103.3 | 84.6 | 78.9 | [2] |
| Lifetime eggs, 29.4 °C | 64.3 | 73.5 | 68.3 | [2] |
| Female longevity, 23.8 °C | 14.71 d | 12.46 d | 12.71 d | [2] |
| Female longevity, 29.4 °C | 9.71 d | 8.79 d | 8.91 d | [2] |
| Female offspring | ~74% | ~55% | ~57% | [2] |
| r_m, 23.8 °C (/day) | 0.219 | 0.204 | 0.207 | [2] |
| r_m, 29.4 °C (/day) | 0.293-0.295 (range across species) | same range | same range | [2] |
Development rates were similar across the three species, and males developed slightly faster [2]. The twospotted spider mite's edge at 23.8 °C came from more eggs and a more female-biased sex ratio [2]. The sex-ratio values are read from a scanned copy of the paper; check the original if you need them exactly.
Which spider mite looks like what? A quick key
- Mite oval, ~0.5 mm, slow, two dark side spots, colour yellow-green: green form of T. urticae.
- Same shape and spots, deep red to carmine: red form of T. urticae ("carmine mite").
- Bright orange, spots faint or absent, not feeding, in cracks or on old leaves: diapausing T. urticae female (either form) [7].
- Bright orange-red, pear-shaped, long legs, runs fast, no spots: Phytoseiulus persimilis, a predator; leave it [7].
- Mites invisible at 10x, twisted or bronzed new growth: not spider mites; see broad and russet mites and hemp russet mite.
Steps 1 and 2 are managed identically.
What are the common myths about red and green spider mites?
The most common myth is that red spider mites are a tougher, separate species; the best current evidence treats them as a colour form of the twospotted spider mite with no proven extra resistance [1].
- "Red spider mites are a different, tougher species." Myth for most purposes: synonymy is the majority view, and resistance has never been compared by colour [1].
- "You can identify the species by colour." Myth. Colour varies with age, diet, cold and hybrid origin [1].
- "Orange mites are carmine mites." Myth. Bright orange females are usually diapausing females [1][7].
- "Red forms never go dormant." Myth. Many fail to diapause, but some populations do [1].
- "Green and red forms need different control." Established that they do not, in the sense that every tactic in the spider mites article applies to both [1][7].
Common mistakes
- Changing products because "it's the red one now"; check instead whether your rotation repeated an IRAC group [13].
- Killing Phytoseiulus persimilis because it is red [7].
- Counting orange diapausing females as "dead" or "gone"; they come back when it warms [1][7].
- Assuming a clean colour means a clean clone; males and juveniles look the same in both forms [1].
Evidence
- Synonymy of T. cinnabarinus with T. urticae: Supported by a comprehensive review with new crossing and morphological data [1]; Contested by some molecular and crossing studies cited there [1].
- Morphological overlap and colour variability: Established [1].
- Diapause variability within both forms: Established [1][12].
- Resistance differences between colour forms: no published comparison [1].
- Heat tolerance differences: no direct comparison found; distribution data only [1].
- Red-form life table: one study on carnation [3]; not comparable host-for-host with green-form data [2][4].
- Other Tetranychus on cannabis: no verified record found; extension hemp sheets list only T. urticae [8][9][10].
Glossary terms used here
- Glossary: diapause, arrhenotoky, life table, intrinsic rate of increase, Phytoseiulus persimilis, two-spotted spider mite
