Thrips are a class of extremely tiny insects – almost microscopic – that either destroy or protect plants. They can be found both in the garden and in the house.
Key thrips facts
Name – Thrips, Frankliniella, Caliothrips among many
Order – Thysanoptera
Lifespan – 60 days
Size – from 1/64th to 1/8th inch (0.2 to 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 (wind-borne)
Nearly 6,500 different species of thrips exist. The great majority of them are beneficial in the garden. Some, however, are truly pests.
What are thrips?
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.
- 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.
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.
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.
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.
- There are different stages in the life of a thrips. These are often found together when they form colonies.
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:
- 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.
Learn about thrips damage in more detail.
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.
- 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.
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.
- Go into more detail about the different thrips species
Predator, recycler and pest thrips
From a practical point of view, it helps to group these insects into different types of thrips according to how they feed.
- Pest thrips feed directly on plants or live plant material.
- Recycler thrips feed on plant debris, dead plant material, or fungus
- Predator thrips feed on other live insects and bugs.
Of course, predator and recycler thrips are beneficial thrips for the garden.
- They help control other pests.
- They also help break soil down to produce nutrients that plants can use to grow.
- More on what makes different thrips types unique
Are thrips dangerous to people and pets?
Thrips aren’t interested in either people or pets. However, it has been shown that when they land on something soft, some thrips try to bite.
- It’s very rare though.
- Not necessarily a sign of defense.
Simply, skin patterns are similar in feel and thickness to some types of leaves, at least from a thrip’s point of view. As such, don’t be surprised that they try to feed off whatever they land on!
It hurts a bit, like the bite of a mosquito, but the itch thankfully doesn’t last as long.
- There isn’t any risk of contamination, disease, or other such ailment (unlike the tick, which is (in)famous for spreading Lyme disease).
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!
Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Leaf with a thrips by Katja Schulz under © CC BY 2.0
Flattened and whitened portions of thrips-infected leaf by Scot Nelson ☆ under Public Domain
Thrips on cute flower by Gary Chang under © CC BY-SA 2.0
Leaf with thrips by Maximilian Paradiz under © CC BY 2.0