Thrips prefer Outdoor-Living, but may hitch Rides to Indoor Plants

Also known as storm flies, thunder blights, thunder bugs or thunder flies, thrips have a slender, cigar-shaped body typically ranging from 0.5 to 1 mm (0.02 to 0.04 in) in length, although predatory thrips can grow to lengths of 14 mm (0.55 in).

Typically light to dark brown in colour, most adult thrips have pairs of fuzzy wings, but many of them will hop rather than actually fly. Those that do fly will move on to neighbouring plants when disturbed, spreading the infestation in the process.

Females produce minute kidney-shaped eggs, from which the typically wingless, yellowish young will hatch. Hatching may, depending on species, take a single day or several weeks.

Though not common on house plants - they much prefer to live on outdoor flowers - thrips may hitch a lift on plants, pets or people to get indoors. Once there, their only choice is to feed on whatever is available, namely house plants. As they reproduce rapidly, it is quite possible to have a full blown infestation within a very short time.

For this reason, it is essential to carefully observe preventative measures, such as isolating new plants and plants returning inside after spending the summer in the garden; washing pots and tools carefully and inspecting plants on a regular basis.

Signs of Infestation

Because thrips rasp into flower petals and leaves to get at the sap, leaves and petals often appear distorted and feature visible scars. Thrips often also leave visible dark spots on flower petals and silvery streaks on foliage. In addition, it may be possible to detect the movement of congregations of larvae on the soil.

Dealing with Infestations

Infested plants should be isolated immediately; followed by removal of affected plant parts. Light infestations can often be removed by simply spraying the plant with water to wash them off. This should be repeated periodically (every couple of days).

Heavier infestations may benefit from sprays containing insecticidal soap or Neem oil, and placing blue (unlike most other pests, which are attracted to yellow, thrips are attracted by bright blue) sticky traps near plants will also help.

Diazinon or malathion sprays, systemic insecticides or biological insecticides, such as, for example, Verticillium lecanii or Beauveria bassiana (both of which have a very clear effect on adults, eggs and larvae of thrips) should help to control more serious, stubborn infestations.

Staff at nurseries/ garden centres or online experts will be able to advise which method will be the most suitable solution under any given circumstances. Naturally, reading labels and following instructions carefully is important.