Spot cards are simple devices for measuring fly activity when lower thresholds are desired, such as when neighbours are close or animal facilities are open to visitors (for example, horse stables).
Spot cards are white 7.5 x 10cm file cards which are fastened flush to pre-chosen locations in a facility.
They are fastened to posts, rafters, partitions, feed troughs, etc., where the animals will not disturb or soil them.
Flies resting on the spot cards leave light straw-colored regurgitation spots and dark faecal spots. The number of spots per card is easy to count after an exposure period of about 3–7 days.
Exposure for longer than 7 days is not practical because the cards become too soiled.
Cards may be labelled, counted, and kept for later reference if needed (such as in legal proceedings relating to fly complaints).
Most spots are caused by the house fly. However, if other flies are present (especially Ophyra spp.), they will spot the cards. Therefore, spot card counts are only an index of fly activity. The species of flies cannot be determined from spot card counts.
Other observations should be made to verify whether or not the house fly is the most abundant species.
The placement of spot cards (like ribbons and jug-traps) is important, and they must be placed where flies are observed to rest or where fly specks are present.
Generally, locations in higher areas, as high as a person can reach, are desirable.
Several cards are necessary depending upon the level of fly activity to be measured, and the precision desired.
At least 10 cards should be used in a facility.
In poultry houses, an index of 50 spots per card per week has been used as a threshold for chemical treatments.
In different situations, lower thresholds may be chosen.
