Thrips (Thysanopteran) are very small insects (one or a few millimeters long) and are famous as pests in the agriculture scene.  Some researchers found thrips in flowers as pollinators.  However, we can see thrips which are obviously not pollinators often in flowers of wild plants.  Why the plants do not avoid or remove these thrips, the famous pests?  We focused on the ecological relationships between wild flowers and thrips.  Our observations on the wild flowers of 403 species clarified that thrips preferred flowers of complicated and deep shape rather than ones of simple and flat shape.  Dissecting 20 heads of Cirsium japonicum showed the microhabitats of thrips in a flower head.  The almost thrips were in the interspace among florets in a head, and only a few thrips were inside florets.  In the heads, there was no thrips eating pollens or drinking the floral nectar neither.  Besides, they did not damage any organs of flowers.  Because the thrips help to exclude fungi and/or other small pests, plants may allow their existence in flowers.  We consider that thrips in a flower may play a role of cleaners for the maintenance of fruit developments.