Triple-spotted Clay (TSC) and Double-square Spot (DSS) are really tricky species to separate with any degree of confidence. Both fly in June – August, both are the same size (fw 17-19mm) and both have a similar basic pattern/markings to the upper forewing. DSS is more common and widespread, which needs to be taken into account.

TSC can be confused with Setaceous Hebrew Character, but mainly with Double Square-spot, which looks very similar. TSC lacks the conspicuous pale wedge on the forewing of Setaceous Hebrew Character.

In comparison to DSS it rests with its wings wrapped together more tightly over the body, giving it a sleek and slender appearance, unlike DSS which shows less overlap and has a broader winged appearance. The ground colour is a rich purplish to reddish-brown, whereas DSS is typically pale brown.

The colour of the hind wings can be of great help. On TSS the hind-wings are a pale creamy grey or light brown, noticeably lighter than the darker forewings. On DSS the hind wings are a smoky, dingy grey-brown colour, with darker veining and similar in tone to or slightly darker than the forewings. On DSS there is a small discal-like spot/chevron mark that exists on the under hind-wing and this mark appears to be a reliable identification feature.

The neck collar on TSC is smooth and nearly monochrome without stark colour contrasts. On DSS there are pale extremities on outer tips of the head creating a pale line from the darket upper section.