Macropis nuda is a ground nesting, univoltine bee native to northern parts of North America.

All species of the genus Macropis are oligolectic, as females forage for loosestrife plant oil to line their nests and provision to their eggs.

Macropis bees are commonly referred to as oil-bees, as they are the main pollinators of oil-plants such as plants of the genus Lysimachia.

Females have dense white scopa on their posterior tibiae that are foraging adaptations used for collecting and carrying floral oils and pollen.

M. nuda has historically been found from British Columbia, Idaho, and Utah east to Newfoundland and New Jersey, though evidence suggests its range may be shrinking due to climate change.

Burrows are approximately 3.0-3.5mm in diameter and are coated with a waterproof lining created from the floral oils collected by the female.

Males and females spend the winter in cocoons as mature pupae, and recommence development in the spring as the temperature increases.

[7] Larvae rapidly develop into pupae within 10 days, feeding on a provision that is a mixture of floral oil and pollen.

The larval feeding period lasts approximately 10–14 days, after which they are pupae and begin to spin cocoons.

Not only does the cocoon allow safety from the cold of the winter, it may also serve as a barricade to protect against parasites and predators.

Females will feed themselves with nectar of a variety of flowers, but will only use oil and pollen from Lysimachia ciliata plants for provisioning.

Females are found around Lysimachia plants in times of full sun and collect oil and pollen simultaneously.

There has been no observed scent marking,[2] and males and females do not produce any kind of sound to attract one another like other solitary bees such as Meganomia.

On warm days, M. nuda females will guard the entrances to their nests, impeding the cuckoo bees' mode of parasitism.