Spear thistle is often a
ruderal species, colonising bare
disturbed ground, but also persists well on heavily
grazed land as it is unpalatable to most grazing animals. The flowers are a rich nectar source used by numerous pollinating insects, including
honey bees,
wool-carder bees, and many
butterflies. The seeds are eaten by
goldfinches,
linnets and
greenfinches. The seeds are dispersed by wind, mud, water, and possibly also by
ants; they do not show significant long-term dormancy, most germinating soon after dispersal and only a few lasting up to four years in the
soil seed bank. Seed is also often spread by human activity such as
hay bales. and a
noxious weed in Australia and in nine US states. Spread is only by seed, not by root fragments as in the related
creeping thistle C. arvense. It is best cleared from land by hoeing and deep cutting of the taproot before seeds mature; regular cultivation also prevents its establishment. Despite this label, the plant has beneficial qualities beyond its very high
nectar production. It produces seeds eaten by the
American goldfinch, down from seed pods that is used by those birds for
nesting material. However, despite this serving
generalist pollinators and animals, it is highly recommended to plant
native thistles and other plants as it can wreak havoc on natural ecosystems. == Other names ==