Barely 3 mm long and shaped like a narrow grain of rice, thrips (order Thysanoptera) carry wings fringed like a feather and rely on the wind to reach new plants. Most species hunt other insects or recycle debris; only a few suck sap and spread viruses, and a magnifying lens is what tells them apart.
Thrips at a glance
Name
Thrips, Frankliniella, Caliothrips among others
Order
Thysanoptera
Lifespan
60 days
Size
1/64th to 1/8th inch (0.2-3 mm)
Danger to plant
rarely deadly, except if spreading virus
Side effects
transmit viral diseases
Beneficial
yes and no, depending on species
Appears in
spring to fall (year-round indoors)
Contagious
very (air-borne)
They can be found both in the garden and in the house. Nearly 6,500 different species of thrips exist. The great majority of them are beneficial insects in the garden. Some, however, are truly pests.
Thrips are tiny animals that are part of the insect world. There are thrips of all kinds: some feed on plants, others chew up decaying matter. Still others are predators that hunt for food, chasing other insects and tiny bugs.
A magnifying glass is needed to see them
They’re extremely small and it’s very hard to see them without a magnifying glass or microscope.
Thrips have a narrow, oval shape, somewhat like a tiny grain of rice.
A common name for thrips is thunderfly. This is because they drop to the ground in large numbers shortly before thunderstorms! The build-up in static electricity interferes with their flying and they simply drop from the sky.
Some thrips pose grave dangers to crops, harvests, and greenhouse growers.
Feeding weakens plants since they suck up sap like a mosquito bites us for blood.
Thrips feed from many different plant species. This makes controlling them difficult. Only a few species like the onion thrips feed on specific plants.
An additional danger is that thrips often spread plant viruses and fungi. Thrips feeding on an infected plant will spread the disease to any other plant it later feeds on.
What do thrips look like?
Thrips are 1/64th to 1/8th inch (0.2 to 3 mm) long, oval-shaped, tiny insects with 6 legs.
They come in many colors from red to blue, but most are brown, yellow, or black.
Wings are made of frills, like the close-up of a bird feather. They’re neither made of scales like the butterfly wing, nor are they a single sheet like wings of dragonflies.
The word “thrips” is always used with an “s” at the end, even when talking of a single individual.
Thrips damage on plants
Thrips species that feed on plants usually damage plants in similar ways. However, each species of thrips is different from the next.
Additionally, most species of thrips feed on different species of plants. Damage due to thrips thus depends on the host plant on one hand and the thrips species on the other.
Main symptoms of thrips are:
Silvery feeding patches later turn tan or brown
Flattened patches on leaves that are white or silver-colored at first and turn tan or brown later on.
Black specks or dots rather randomly distributed along infected areas. These can be brushed or shaken off.
White dots on leaves or stems where eggs are lain.
Folded leaves with the thrips hiding inside (common on the Ficus tree, for instance)
Like many insects, thrips are born from eggs and go through several stages. For thrips, depending on the species, between 4 and 6 stages are needed for an egg to become a mature adult.
Thrips stay on the same host plant
Stages differ from one to the next. Wings, for example, may only appear in the last one or two stages.
Thrips spend most of their lives on the same host plant. The last stage before adulthood is often spent in the ground at the foot of the plant.
More curiously, in some stages, the thrips doesn’t even feed at all, just like the cocoon stage of caterpillars.
Adults can fly, albeit not so well. They rely on wind to reach other plants.
Thrips go from hatching to adult within 1 to 3 weeks. Many species of thrips, as adults, have a lifespan of up to two months.
Treat thrips resistance as a matter of degree rather than a guarantee, since most garden plants rated resistant can still be damaged under heavy pest pressure or unfavourable growing conditions.
In onions and leeks, glossy or semi-glossy cultivars generally host fewer onion thrips than waxy blue-green types, though the effect varies with conditions and the underlying mechanism remains uncertain.
Resistance to a thrips-transmitted virus can keep the pathogen from establishing in a plant, but the insects themselves still feed and scar the leaves, so monitoring remains necessary.
Types of thrips
Two major families of thrips
Biologically speaking, thrips are classified into two different branches (sub-orders) within the Thysanopthera order.
To tell them apart, look at the very last segment of the thrips:
The Tubulifera sub-order has a last segment that is long and cylindrical, like a tube.
The Terebrantia sub-order has a pointed segment. Inside is a saw-like stinger the female uses to lay eggs inside plants. This organ is called an ovipositor. See one in this article describing thrips eggs and ovipositors.
Many pest thrips are from the Terebranthia order. Even before they’re born, the mother is already attacking plants to lay the eggs inside! The Tubulifera order also counts severe pests, too.
Pest, recycler or predator: telling thrips apart by how they feed
Not every thrips on a plant is doing harm. Grouping them by what they eat is the quickest way to know whether to act or to leave them alone.
Pest, recycler or predator: telling thrips apart by how they feed
Type of thrips
What it feeds on
Effect in the garden
Pest thrips
Plants or live plant material
Weakens plants by sucking sap, and can spread viruses and fungi
Recycler thrips
Plant debris, dead plant material or fungus
Beneficial: helps break soil down to produce nutrients
Predator thrips
Other live insects and bugs
Beneficial: helps control other pests
Only the first group calls for treatment; the other two are allies worth keeping.
Smart tip about thrips
Carry a magnifying lens around when on the lookout for these. Sometimes, you’ll have to cut a flower bud open to discover them hiding and feeding inside!
Written by Gaspard Lorthiois | Loves helping out, especially when it comes to growing things. Worked in herbal medicine, runs a farm, and dabbles in tech. Master's degree and engineer.
