Harmless. No sting, no bite, nothing that reacts with skin. The only thing it costs anyone is brassica leaves, and that is the caterpillar's doing rather than the butterfly's.
SizeWingspan 45–55 mm
MarkingsPlain chalky white above with black wingtips · One black spot on each forewing in males, two in females
WhereGardens, allotments, farmland and waste ground — anywhere brassicas or wild mustards grow.
SeasonEarly spring through autumn, in several overlapping broods
How to tell it apart
Plain chalky white above with black wingtips
One black spot on each forewing in males, two in females
Underside of the hindwing is pale yellow-green, visible at rest
Wingspan 45–55 mm, with a restless low fluttering flight
Caterpillar is velvety green with a faint yellow line, on cabbage and kale
Where you’ll find it
Across the entire United States. Introduced from Europe in the 1860s and now one of the most widespread butterflies on the continent.
Gardens, allotments, farmland and waste ground — anywhere brassicas or wild mustards grow.
Early spring through autumn, in several overlapping broods.
How it behaves
The white butterfly crossing almost every American garden is this one, and its abundance is the point: it produces several broods a year, uses both cultivated brassicas and wild mustards, and tolerates disturbed ground better than most native butterflies. Males patrol low over vegetation looking for females rather than holding territory. The caterpillars feed openly on leaves rather than hiding, which is why the damage is obvious before the animal is.
You’ve found one indoors
If you grow brassicas and want them intact, fine netting before the butterflies arrive is the only thing that reliably works — picking caterpillars off is endless once eggs are laid. Nothing needs spraying for the butterfly itself, which does no damage at all.
Common questions
Is every white butterfly a cabbage white?
Most in a garden are. Pale female clouded sulphurs are whitish and get mistaken for them, and a few native whites overlap, but the plain white butterfly around vegetables is nearly always this.
How do I tell males from females?
Count the forewing spots. One black spot means male, two means female. It is visible in most photographs.
What is eating my cabbages?
If the caterpillar is velvety green with a faint yellow stripe and sits openly on the leaf, this. If it is smooth and loops as it walks, that is a cabbage looper, which is a moth.
Jon Sullivan · CC-BY