Tephritis formosa is a species of tephritid fly. It is one of many species known commonly as gall fly. It is found in most countries across Europe and it also occurs in the Near East. The adult female is about 5 to 6 mm in length with wings of about 4 to 5 mm. The male is 4 to 5 mm long with wings about 4 mm long. The host plants for the larva are hawksbeard, cat's ear and sow-thistle. It invades the flower heads, causing galls to form.