Thrips (Order: Thysanoptera)

A photograph of an adult thrip _Thrips palmi_.

Some species of thrips, like Thrips palmi (depicted), are major crop pests.
J. Marie Metz, USDA

Thrips are also known as thunder flies, because they sometimes take to the air in huge numbers (especially in thundery weather) and are occasionally irritating as they can get into people's eyes when they fly around like this.

Thrips found in the British Isles are tiny insects, just 1-2mm long, but in other parts of the world they can be up to 14 mm. They have two pairs of narrow, fringed wings, although some are wingless. The scientific name for the order - Thysanoptera - comes from the Greek thysanos (fringe) and pteron (wing).

They are not difficult to spot, as they are often found on flowerheads. A close look at a dandelion often reveals a number of them. And they are rather interesting creatures.

More than 6,000 species of thrips are known around the world, with over 300 of these in Europe and only around 150 native to Britain. Telling these tiny insect species apart is not always easy!

And before we go any further - a single thrips is still a thrips - not a thrip (just like a single sheep is a sheep)!

What's special about thrips?

Thrips are certainly a little bit special among the insects.

They are special firstly because of their life cycle. Insect life cycles can be described as either complete or incomplete. Insects that have the so-called 'complete' life cycle go through the stages of being an egg, from which emerges a larva, which then becomes a pupa (within which their wings develop) and then an adult emerges from the pupa. Essentially, incomplete life cyclers miss out the pupal stage and the larvae (called nymphs) look like their parents.

Thrips do have this complete life cycle - except that their wings develop outside the pupa, which makes one wonder why they bother to have a pupa at all. Not only that, but they have more than one pupal stage. Yet, during their larval stages, they look like miniature adults!

Another odd thing about thrips is their mouthparts. They lose one half of their mandibles during development, so they are lop sided, or asymmetrical, with only one mandible on the left hand side!

Thrips families

The Thysanoptera are divided into two main sub-orders, each of which is further subdivided into families:



Friend or foe?

Thrips are generally harmless and rather endearing little creatures (well, the writer thinks so anyway). But some species of thrips are regarded as pests on certain crops.

For example, Thrips palmi is a notifiable pest in the UK. It can cause damage to a wide range of glasshouse crops, such as cucumber, aubergine and sweet pepper. Adults and nymphs feed by sucking the cell contents from leaves, stems, flowers and the surface of fruits, thereby causing silvery scars and leaf chlorosis.

But like many so-called pests, this species of thrips originates from abroad (introduced by man with plants from south-east Asia and elsewhere) and so it tends to be found in glasshouses rather than in the garden.

However, it is also a species of thrips - the Pea Thrips, Kakothrips robustus - that is responsible for the mottled silvery appearance of many pea pods.

Finding thrips

The best way to catch and examine thrips is by beating or sweeping vegetation, using a sweep net (a strong net with a cotton bag) or beating tray (or upturned umbrella). You will then need a hand lens to examine them closely. Alternatively, close examination of flower heads in the garden in the spring and summer will reveal loads of these little animals.

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