Invertebrates
Thrips
Thysanoptera · also called thunderflies, thunderbugs
A thrips is barely large enough to see clearly, a sliver of an insect with fringed wings and an oddly lopsided mouth built to pierce a single plant cell at a time. On its own it is a minor nuisance. In large numbers, especially in the close, humid air before a thunderstorm, thrips become the “thunderflies” that land on skin and prickle, and on farms they are a serious pest, both for the damage they do directly and for the plant viruses they carry between crops.
Overview
Thrips are the order Thysanoptera — tiny, 1–2 mm, cigar-shaped insects with narrow, fringed wings found on flowering plants worldwide. Most feed on plant cell contents using a unique, asymmetrical mouthpart with a single piercing mandible, while a smaller number are predatory on mites and other tiny insects.
Thunderflies and viruses
Large numbers become active in hot, humid weather ahead of thunderstorms, landing on skin with a faint prickle rather than a true bite. Beyond direct feeding damage — scarred, silvered, or distorted leaves and fruit — several thrips species spread serious plant viruses between crops, often a bigger economic threat than the insects themselves. Many species reproduce by parthenogenesis, letting populations explode within weeks under warm conditions.
Status
Least Concern — abundant worldwide and, if anything, expanding, with pest species spread far beyond their native range through the international plant and produce trade.
Thrips: common questions
Do thrips bite people?
Thrips do not bite or feed on people in the way a mosquito or a bedbug does, since their mouthparts and digestive system are adapted specifically for piercing plant cells rather than skin, but during hot, humid, thundery weather large numbers can become active and land on exposed skin, where their small, sharp mouthparts can produce a brief, prickly, itching sensation as they probe experimentally, sometimes described as feeling like a static shock or a pinprick. This is a minor irritation rather than a genuine bite, and it does not transmit any disease to people.
Why are thrips called thunderflies or thunderbugs?
The names come from the well-known pattern of thrips becoming suddenly abundant and highly active during hot, close, humid weather of the kind that often precedes or accompanies thunderstorms, when rising temperature and humidity trigger mass movement and flight in local populations. Swarms appearing just before a storm, sometimes landing on people's skin, clothing, and windows in large numbers, gave rise to the folk names thunderfly and thunderbug long before the underlying weather-driven biology was well understood.
How do thrips damage plants?
Thrips damage plants in two main ways. Directly, their piercing-and-sucking feeding on individual cells in leaves, flower petals, and developing fruit leaves behind tiny scars, silvering, discoloration, or distorted growth, which can significantly reduce the visual quality and market value of ornamental plants and crops even without killing the plant outright. Indirectly, and often more seriously for agriculture, several thrips species act as vectors for plant viruses, picking up virus particles while feeding on an infected plant and transmitting them to healthy plants they visit afterward, which can cause much more extensive crop losses than the physical feeding damage alone.
How can thrips populations grow so quickly?
Several biological traits combine to let thrips numbers explode rapidly under good conditions. Many species can reproduce by parthenogenesis, meaning females can produce offspring without mating with a male, removing the need to find a mate before reproducing. Generation times are also short, sometimes just one to a few weeks in warm conditions, and a single female can lay a substantial number of eggs over her lifespan. Combined with their tiny size, which lets large numbers develop unnoticed in a small space such as a single flower bud or leaf cluster, these traits allow thrips populations on a host plant or in a greenhouse to increase from barely noticeable to a serious infestation within a short period.