Ohio State University Extension Fact Sheet

Ohio State University Extension Fact Sheet


1991 Kenny Road, Columbus, OH 43210-1090

Grass Thrips


William F. Lyon

Common Name Scientific Name
Grass Thrips Anaphothrips obscurus (Mull.)
Onion Thrips Thrips tabaci Lindeman
Pear Thrips Taeniothrips inconsequens (Uzel)

Grass Thrips or "Oat Bugs" occasionally bite people. Bites produce an itching sensation usually causing a skin rash. When swarming in enormous numbers, they annoy people by getting in their eyes, nose, mouth and clothes. Many enter the home from fields and neighborhood yards. These plant-feeding pests are attracted to potted plants with excess water in their drainage pans, hitchhike indoors on cut flowers, occur near swimming pools, ornamental waterfalls, grassy areas, etc. Thrips are very small (less than 1/8 inch), and are responsible for entomophobia or delusionary parasitoses.


Adult thrips are very active and usually less than 1/8 inch long, tan-to-dark brown bodied with four very thin, veinless, featherlike wings. The wing margins are fringed with close-set long hairs. Wings are laid back over the body while at rest. The head has compound eyes and less noticeable, simple eyes. Mouthparts are rasping-sucking. Nymphs are creamy white and wingless. Eggs are laid on the tissues of plants or inserted into plants. Magnification is required for best identification.

Life Cycle and Habits

Thrips are serious pests on vegetables (especially onions) and flowers (chrysanthemum, gladiolus, iris). Plant injury is caused by both nymphs and adults rasping the bud, flower and leaf tissues of the host plants, and then sucking the exuding sap. This causes distorted and discolored flowers or buds and gray or silvery, speckled areas on the leaves. Gladiolus thrips also feed on the corms in storage, causing russeted areas and lowering vigor, which retards growth and makes the flowers smaller.

After successful mating, eggs are laid on plants with the young developing to maturity in about two or more weeks. The number of generations produced each year depends on the thrips species, temperature and other climatic factors. Most species produce many generations in a season. Females may lay fertilized or unfertilized eggs, the latter developing into males only. (Parthenogenesis is reproduction without a male.) There are four or more nymphal instars exhibiting gradual metamorphosis. Both nymphs and adults overwinter concealed in grass stems or other plant debris with activity continuous in warmer climates.

Control Measures

Try to locate the source of infestation. Nursing homes, interior scapes, greenhouses, grassy areas, pool areas, etc. may produce the habitat and food sources for a thrips population. Check for host plants such as potted plants, vegetables, flowers, fruit trees, etc. Thrips may feed between the leaves well down toward the plant base where it is difficult to see. Be sure to check swimming pools or ornamental waterfalls nearby. Collect specimens in vials of rubbing alcohol for accurate species identification.

To reduce and eliminate a thrips infestation, remove excess water around plants and vacuum up thrips. Discard infested plants or treat with insecticides labeled for the host plant. Surface applications may aid in control efforts. Review labels before selection and application of any pesticide. Several species of lady beetles and the minute pirate bug are thrips predators.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-6181

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