They have a slender body and three pairs of legs. Thrips vary in color from dark brown to yellowish. They are active insects and move about rapidly when disturbed. Adult and immature individuals are found together on the plant and there are several generations per year.
Thrips rasp the leaf surface with special mouthparts and then suck up the plant juices.
Such feeding causes the surface of the leaf to become whitened or silvery and somewhat flecked or stippled in appearance. The damage caused by thrips is largely aesthetic. There is no evidence that feeding by thrips causes a reduction in either yield or quality of alfalfa hay. Thrips may play an important role in alfalfa by serving as prey for various predatory insects found in alfalfa. Nymphs of western flower thrips can also be important predators of spider mite eggs.