Larvae and adults of Haplothrips faurei (Hal.) that prey on the tetranychid mites Panonychus ulmi (Koch) or Bryobia arborea Morgan and Anderson attacked mainly the eggs. When no eggs were present, they attacked the motile stages of the mites but their growth and oviposition were slowed. Adult thrips that fed on winter eggs of the tetranychids lived only a short time, unless they also had access to peach leaves. The mite Aculus cornutus (Banks) and fresh pollen of Chenopodium album L. were eaten by H. faurei; pollen was less satisfactory than tetranychid eggs for growth and oviposition. Adults lived for long periods on leaf juices alone.

One larva ate an average of 143 summer eggs of P. ulmi during its developmental period of 8 to 10 days at 24 °C. An adult ate an average of 44 eggs per day at 24 °C. when fed ad libitum.

Females did not fly when fully fed and ovipositing, but they did so during the preoviposition period and after a short period of starvation.

Most individuals of all stages of H. faurei were on the twigs, in crevices find other places of concealment on peach trees, bur a greater proportion of individuals were on the leaves of apple and plum. This difference in distribution was attributed to differential effects on behaviour by the glabrous foliage of peach and the pubescent foliage of apple and plum. The presence of H. faurei on twigs complicated population sampling in peach orchards.

The egg was the stage most sensitive to low humidity, but there was no evidence that humidity limited the population in orchards.

H. faurei was usually scarce in spring. Later, its numbers usually increased with those of the mites and it may have retarded growth of the mite populations, but its most obvious effect was the destruction of winter eggs in the fall.