They range in size from too small to see to about five millimetres. They love wet soil and while they may attack tender, new growth, they prefer material that is already dead. If you have them you could be over-watering. Try treating the soil with Pyrethrum or Malathion at the rates mentioned earlier. Transplanting to new sterile soil after washing the roots is another control.
Thrips are small, thin pests, the young being yellow and the adults brown or black.
The adults are winged and tend to fly around the plant when disturbed. They rasp the plant tissue and suck the juice, leaving silver specks on the surface. Their black droppings can be seen on a badly infested plant. Females leave a small scar on the tissue where they deposit their eggs. Decent control can be achieved with the same materials used on aphids.