Spotted knapweed (Centaurea maculosa or C. stoebe ssp. micranthos, Asteraceae) is an invasive plant that has spread throughout most of North America since being introduced here from Europe in the late 1800s. It outcompetes and displaces native plant species through a variety of traits including phytotoxicity (it literally poisons other plants). By disrupting food webs and reducing biodiversity it has become a serious problem in ecologically sensitive areas.
In spite of its infamy, spotted knapweed flowers produce nectar like any other. A couple of weeks ago I found this flower fly (Diptera: Syrphidae: Taxomerus geminatus) feeding on a knapweed along a driveway here in southeast Michigan.
This unusually warm day brought out a number of insects to feed on the limited late-season plants. With our low temperatures now dipping below freezing and highs only in the 40s F, insects will be few and far between until spring.