🐛✗ Tested and false“Misting your plants or raising the glasshouse humidity will get rid of red spider mite”
Raising humidity slows this mite down rather than removing it. Regular syringing and spraying of plants with water, and maintaining high humidity, reduce the risk but will not, on their own, control the mite. Garden Organic frames the same practice as keeping the pest in check through misting or damping down the glasshouse floor, not as an eradication method. Both sources treat it as one part of a routine, not a fix on its own.
Our read The two sources describe the same limited effect from different angles: RHS as a reproduction-rate slowdown, Garden Organic as a preventative habit. Neither claims misting clears an existing infestation.
What to do: Mist and damp down as prevention alongside good ventilation, but treat an actual infestation with a predatory mite or midge rather than expecting humidity alone to solve it.
In Scotland: A cool, poorly ventilated Scottish glasshouse that gets misted heavily without matching ventilation trades one problem for another: grey mould thrives in the same damp, still air this practice creates.
2 sources
- RHS: Glasshouse red spider miteRegular syringing and spraying of plants with water, and maintaining high humidity, reduce the risk but will not, on their own, control this mite.
- Garden Organic: How to tackle red spider mitesRaising humidity through misting or damping down the glasshouse floor in sunny weather helps keep the mite under check, alongside a warning that too much moisture can encourage fungal disease.
“Red spider mite is an insect”
It is a mite, not an insect, and not a true spider either despite the common name. The RHS classifies it directly as an arachnid, part of the group Acari, and describes it as under 1mm long and yellowish-green when active. Garden Organic makes the same point from the other direction, noting that despite the name, these are not spiders. Both sources agree the mite has eight legs as an adult rather than the six of an insect, placing it with ticks and true spiders rather than with aphids or whitefly.
What to do: This matters for control choices: insecticides aimed at true insects are not built for mites, which is part of why the recommended control is a predatory mite or midge rather than a generic bug spray.
2 sources
“Red spider mite only attacks greenhouse and polytunnel crops, never plants growing outside”
This mite can also feed on garden plants during summer and can cause problems outdoors, especially in hot, dry weather. It is not confined to covered crops; it simply thrives fastest wherever conditions are warm and dry, which a glasshouse supplies reliably and open ground usually does not.
Our read The claim survives in a weaker form: this mite is overwhelmingly a glasshouse and polytunnel problem in Scotland specifically, because the crops most named against it (tomatoes, cucumbers, peppers, aubergines) need cover to grow here at all, and a hot, dry outdoor spell long enough to matter is the exception rather than the rule this far north.
What to do: Prioritise checking under-cover crops, but do not assume outdoor plants are automatically safe during a genuinely hot, dry Scottish summer, particularly runner beans and strawberries grown outside.
In Scotland: Runner beans are the one outdoor Scottish crop named against this mite independently of its glasshouse hosts, which is the clearest sign the outdoor risk is real here even though it is uncommon.
2 sources
“Watching for fine webbing on the leaves is how you catch a red spider mite problem early”
Webbing is a late-stage sign, not an early one. The RHS notes that in heavy attacks a fine silk webbing may be seen on the plants, by which point leaves are already losing colour and drying up or falling. Garden Organic places webbing after the mottled discolouration and puncture-mark damage has already developed, describing it as something you notice once large numbers of mites are present. By the time webbing is visible, the population has already built to the point of doing real damage.
What to do: Check the undersides of the oldest leaves with a hand lens for early pale mottling or tiny yellow-brown dots, and shake a suspect leaf over white paper to spot moving mites, rather than waiting for webbing to confirm the problem.
2 sources
“Introducing predatory mites like Phytoseiulus persimilis is an effective way to control red spider mite”
This is the established, first-choice control rather than a fallback. The RHS names Phytoseiulus persimilis as the most commonly used biological control for this mite, released as nymphs and adults that prey on all its life stages, and notes it can succeed against outdoor infestations in summer too. Garden Organic goes further, reporting that commercial glasshouse growers have adopted it widely because they have found it cheaper, safer and more effective than synthetic chemical sprays.
What to do: Wait until damage is actually visible before releasing it, and only once the glasshouse or polytunnel is reliably at 15°C or above, since the predatory mite will not establish in cooler conditions.
In Scotland: The 15°C threshold is worth checking rather than assuming, particularly early or late in the Scottish growing season when an unheated structure may not have reached it yet.
2 sources
- RHS: Glasshouse red spider mitePhytoseiulus persimilis is the most commonly used biological control for red spider mite, and can be successful against it on outdoor plants in summer too.
- Garden Organic: How to tackle red spider mitesPredatory mites are so effective that commercial glasshouse growers have widely adopted them, finding them cheaper, safer and more effective than synthetic chemicals.
