Published September 3, 2026
Almost every single bee covered on this site forages for essentially the same two basic things — nectar and pollen. Oil-collecting bees break that pattern entirely: certain native bees, most notably in the genus Macropis, gather floral oil from specialized flowers as a genuinely distinct third resource, using it for purposes nectar and pollen can’t serve. This genuinely extreme, well-documented dietary specialization sits alongside the squash bee as one of the more striking examples of native bee dietary specialization covered on this site.
Table of Contents
- What Are Oil-Collecting Bees?
- Macropis: North America’s Primary Oil-Collecting Genus
- An Extreme Case of Plant Specialization
- How the Oil Is Actually Collected
- What the Collected Oil Is Actually Used For
- Elaiophores: Flowers Built to Produce Oil
- Cuckoo Bees That Target Macropis Nests
- Tropical Relatives: Centris and Other Oil Bees
- Nesting Behavior
- Why This Specialization Matters for Conservation
- Sting Risk to People and Pets
- Common Identification Mistakes
- Frequently Asked Questions
What Are Oil-Collecting Bees?
Oil-collecting bees are bees that gather floral oils from certain specialized flowers in addition to, or instead of, relying solely on nectar and pollen. This is a genuinely unusual foraging behavior in the bee world; the great majority of bee species, including honeybees and most native bees covered elsewhere on this site, never collect floral oil at all, since most flowers don’t produce it in any meaningful quantity.
Macropis: North America’s Primary Oil-Collecting Genus
In North America, the primary native oil-collecting bee genus is Macropis, a small group of species in the family Melittidae. These bees are found across much of the continent, though because of their specialized biology and comparatively small populations, they are far less commonly noticed than more generalist native bees like mining bees or sweat bees.
An Extreme Case of Plant Specialization
Macropis bees show an extreme degree of host-plant specialization, foraging almost exclusively on flowers in the genus Lysimachia (commonly called yellow loosestrife), which are the primary plants documented to produce the floral oils this bee genus depends on. This narrow specialization goes even further than the pumpkin-and-squash-only foraging pattern of the squash bee, since Macropis bees depend on their host plant for a resource — oil — that few other flowers provide at all, rather than simply preferring one plant family among many that could theoretically substitute.
How the Oil Is Actually Collected
Female Macropis bees have specialized, dense hairs on their front and middle legs adapted specifically for absorbing and transporting floral oil, distinct from the pollen-carrying structures found on the hind legs of most bees. A foraging female uses these specialized hairs to soak up oil secreted by the flower, then transports it back to her nest much the way other bees transport pollen, representing a genuinely separate collection-and-transport system layered on top of typical bee foraging anatomy.
What the Collected Oil Is Actually Used For
The floral oil collected by Macropis bees serves at least two documented purposes: it is mixed with pollen to create a nutrient-rich larval food provision, and it is also used to waterproof the walls of the underground brood cells where offspring develop. This waterproofing use is a genuinely interesting parallel to the plasterer bee covered elsewhere on this site, which achieves a similar waterproofing outcome using a different glandular secretion rather than collected floral oil — two unrelated native bees arriving at a similar nest-protection solution through entirely different biological means.
Elaiophores: Flowers Built to Produce Oil
The flowers that produce collectible floral oil have specialized oil-producing glandular structures called elaiophores, an adaptation found in a relatively small percentage of flowering plant species worldwide. This represents a genuine, coevolved plant-pollinator relationship: the plant produces a specialized reward that most pollinators can’t use or don’t seek out, while the specialized oil-collecting bee depends on that exact reward, creating a tightly linked relationship between a narrow set of plants and a narrow set of bee specialists.
Cuckoo Bees That Target Macropis Nests
Like several other specialized native bees covered on this site, Macropis bees have their own documented cleptoparasite: certain species in the related genus Epeoloides are known to invade Macropis nests and lay their own eggs there rather than provisioning a nest of their own, relying entirely on the host bee’s oil-and-pollen provisions to raise their offspring. This parasitic relationship is itself considered rare and closely tied to the health of local Macropis populations, since a cuckoo bee specialized this narrowly can only persist where its specific host is also present in sufficient numbers.
Tropical Relatives: Centris and Other Oil Bees
While Macropis is the primary oil-collecting genus relevant to most of North America, oil collection as a broader bee behavior is considerably more diverse in warmer regions, including the genus Centris, found in the southwestern United States, Mexico, and further south into Central and South America. Centris bees forage on a wider range of oil-producing flowers than Macropis, reflecting the greater diversity of elaiophore-bearing plant species found in tropical and subtropical regions compared to the temperate zones most of this site’s readers garden in.
Nesting Behavior
Macropis bees nest in the ground, typically in damp or wetland-adjacent soil near where their Lysimachia host plants grow, digging burrows that lead to individual brood cells. This ground-nesting, solitary lifestyle follows the same general pattern seen across most native bees covered on this site, with the key difference being the oil-waterproofed cell lining described earlier, which is specific to this genus and closely tied to its unusual foraging behavior.
Why This Specialization Matters for Conservation
Because Macropis bees depend so heavily on a narrow set of host plants, their populations are directly tied to the health and availability of Lysimachia stands in a given area, making habitat loss or wetland-adjacent land-use change a more direct threat to this species than it would be to a generalist forager with many alternative food sources. This is a useful, honest illustration of why native bee conservation often depends on protecting specific plant communities rather than simply planting “pollinator-friendly” flowers in general.
Sting Risk to People and Pets
Macropis bees pose essentially no meaningful sting risk to people. Like most solitary native bees covered on this site, they are not aggressive and have no colony to defend, making unprovoked stings extremely rare and generally limited to situations involving direct handling.
Common Identification Mistakes
The most common mistake is assuming any bee visiting yellow flowers is simply foraging for nectar and pollen the way most bees do, without recognizing that a bee specifically and repeatedly visiting Lysimachia flowers may be engaged in the genuinely distinct behavior of oil collection. A second common mistake is assuming all native bee specialization looks the same; oil collection is meaningfully different from simple pollen-source preference, since it involves an entirely separate resource and dedicated collecting anatomy rather than just a narrowed food choice.
When during the year are Macropis bees active?
Their active season generally aligns with the bloom period of their Lysimachia host plants, typically summer months, and like most solitary bees, adults are active for a limited window each year rather than being seen throughout every season.
Do male Macropis bees collect oil too, or only females?
Only females collect floral oil, since males play no role in nest construction or provisioning; this follows the same general division of labor seen across nearly all solitary bees, where nest-related foraging and construction tasks fall entirely to females.
Do Macropis bees also collect pollen from other plants besides Lysimachia?
Pollen foraging is generally as narrowly specialized as the oil collection itself, with these bees relying primarily on Lysimachia pollen as well as the oil, reinforcing just how tightly this bee’s entire life cycle is tied to a single plant genus rather than pollen and oil coming from separate, unrelated sources.
Is there any competition between oil-collecting bees and honeybees for the same floral resources?
Meaningful competition is unlikely given how specialized Macropis foraging is; honeybees don’t collect floral oil and generally show little interest in Lysimachia flowers compared to more typical nectar-rich blooms, so the two occupy largely separate ecological niches even when both are present in the same landscape.
Are oil-collecting bees found in home gardens, or mainly in wild habitat?
They are more typically associated with wetland edges, damp meadows, and similar semi-wild habitat where Lysimachia naturally grows, rather than typical home garden settings, though a garden with an established, intentionally planted patch of the right Lysimachia species near consistently moist soil could realistically support them.
How rare are Macropis bees compared to more familiar native bees like bumblebees?
They are considerably less commonly encountered than generalist native bees such as bumblebees or mining bees, both because their host-plant specialization limits where they can live and because their populations tend to be smaller and more localized, making them a genuinely notable find for anyone who does spot one.
What size are Macropis bees compared to a honeybee?
They are generally comparable in size to a honeybee or slightly smaller, without any particularly distinctive size difference that would make them stand out at a glance the way some larger native bees do, which is part of why species-level identification usually requires closer observation of foraging behavior rather than size or color alone.
Are there other North American bees that collect floral resources besides pollen, nectar, and oil?
Floral oil collection is the most well documented alternative resource among native bees discussed on this site, though certain other specialized behaviors exist among bees more broadly worldwide, such as resin collection used by some tropical species for nest construction; within North America specifically, oil collection by Macropis remains the most notable example most readers are likely to encounter.
Is Macropis the only oil-collecting bee genus native to the continental United States?
It is the primary and most widely documented one, though the broader family Melittidae, which Macropis belongs to, includes other specialized genera with their own narrow foraging relationships, reinforcing that this family as a whole tends to produce unusually specialized bees compared to more generalist families.
Can gardeners realistically expect to attract Macropis bees the way they might attract bumblebees?
Realistically, this is a harder species to intentionally attract than most native bees covered on this site, since it requires the right host plant, suitable damp nesting soil nearby, and often proximity to an already-existing wild population, making it more a matter of preserving suitable habitat where the species already occurs than actively drawing it into a typical home garden from scratch.
Has floral oil collection in bees been studied for very long, or is it a recent scientific finding?
The broader phenomenon of floral oil collection by specialized bees has been documented in the scientific literature for many decades, though it remains far less widely known to the general public than more familiar bee behaviors like pollen collection, largely because the plants and bees involved are considerably less commonly encountered than typical garden pollinators.
What happens to a Macropis nest if its Lysimachia host plants disappear from an area?
Because the species depends so completely on this one plant genus for both oil and pollen, the local population would be expected to decline and eventually disappear from that specific area if the host plant were lost, underscoring once again why this bee’s conservation is really a plant-conservation question first.
Frequently Asked Questions
Are oil-collecting bees dangerous to people?
No. Like most native solitary bees, they are not aggressive and pose essentially no meaningful sting risk under normal circumstances.
How can I attract oil-collecting bees to my garden?
Planting or preserving Lysimachia (yellow loosestrife) species is the most direct way to support Macropis bees specifically, since their extreme host-plant specialization means unrelated “pollinator-friendly” plantings generally won’t support this species the way they would more generalist native bees.
Do honeybees ever collect floral oil?
No, honeybees are not documented oil collectors; floral oil collection is a specialized behavior found in certain native solitary bee lineages rather than in honeybees or most other managed or commonly observed bee species.
Is Lysimachia the same plant as purple loosestrife, an invasive species?
No, these are different plants despite the similar common name. Yellow loosestrife (Lysimachia) is unrelated to purple loosestrife (Lythrum salicaria), an unrelated and separately documented invasive wetland plant, and the two shouldn’t be confused when discussing this bee’s host plant.
