Look for glasshouse red spider mite in winter

In the winter, these mites develop thier distinctive orange-red color. Outdoors, they are most active and noticeable from March to October. In heated greenhouses, however, they can be active all year. 

Symptoms of a glasshouse red spider mite problem include a fine pale mottling on the upper surface of leaves as well as the presence of mites, white skin casts, and/or egg shells on the leaf undersides. In heavy infestations, a fine silk webbing can be seen on the plants, usually between leaflets or at leaf nodes. Leaves may lose most of their green colour and dry up or fall off. Severely damaged plants often weaken and die.