wild bees and native bees

The link between honey bees and resin bees

A honey bee is not a resin bee, at least not by definition. But if you compare the behavior of honey bees and resin bees, you will find uncanny similarities.

I was a beekeeper for many years before I began to understand bees. Insight finally came, but not from studying honey bees. Only when I began to contrast honey bees with the rest of them did the bee world begin to make sense. Resin collection is a perfect example of cross-species behavior.

Honey bees are the outliers

Honey bees are outliers in the bee world, unique in many ways. But they are also surprisingly similar to other species, sharing any adaptation that proved useful through the ages.

Remember that Apis mellifera is just one species of about 20,000 named species and perhaps another 20,000 unnamed ones. Scientists have to guess at the total number because many species are tiny with small ranges. And sadly, many are endangered or have already gone extinct, even before we’ve had a chance to name them.

Resin bees are a type of mason bee

Resin bees are a large group of solitary bees belonging to the Megachilidae family. Technically, resin bees are mason bees, and like other mason bees, they build structures with materials they find in their environment. You may be familiar with mason bees that collect mud or tiny pebbles, but resin bees collect—you guessed it—resin. The resin they use is exuded from the stems, buds, and bark of various plants, especially the conifers.

Unlike sap, which is mostly water, plant resins are insoluble in water, often with a glossy appearance. Resins are often sticky, flammable, and may be brightly colored in shades of red, yellow, and brown. They contain a variety of complex organic compounds which are useful to bees.

Resin bees collect a ball of exudate in their mandibles and carry it home to their nests. Like other bees in the Megachilidae family, these bees nest in the long and narrow cavities of hollow reeds, insect burrows, or even soda straws. The resin is used to line the nest cavity and to build partitions between consecutive egg chambers or cells.

Resin bees: an Australian resin bee completes her nest

This striking Australian resin bee is putting the finishing touches on her nest entrance. First she seals the nest with resin for waterproofing, then she adds a layer of mud. Photo courtesy of Mark Berkery.

Laissez faire child rearing

After she has lined the nesting cavity with resin, the female places a ball of pollen mixed with nectar in the far end, lays an egg on top of the ball, and then builds a partition of resin. She repeats the process over and over until the entire cavity is filled, one egg to a cell. The concept of “one egg to a cell” should be familiar to any beekeeper because honey bees, too, build a separate cell for every egg.

Like most other solitary bees, once the female seals a cell, she is finished rearing that particular offspring. Eventually, the egg will transform into a small larva. This larva will eat the ball of pollen and nectar until it is gone. Then it will defecate, spin a cocoon, and pupate. This type of feeding—“Here’s the food, kid. Now you’re on your own,”—is called “mass provisioning,” meaning the provisions are supplied en masse. One and done. The kind of feeding that honey bees do is called “progressive” feeding, because the larvae are fed continually until they spin a cocoon.

The benefits of resin

The resin from plants provides several benefits to these bees. It provides waterproofing for both the interior of the nest cavity and the entrance, and many of the chemicals in resin have antibacterial properties that help to prevent disease in the developing larvae. This, too, should sound familiar to any beekeeper, because honey bees also collect resin.

Although we don’t think of honey bees as resin bees, the collection of plant resins is vital to the health of a honey bee colony. Honey bees collect resins from similar sources: bark, buds, and stems. The honey bees stuff these resins into their pollen baskets and carry them back to the hive. Inside the hive, the resins are kneaded with their mandibles and mixed with bee saliva and beeswax. Once the material becomes soft and malleable, the workers smear it on rough surfaces, cracks, holes, or any place where they want a smooth, waterproof, or antimicrobial surface. Resin processed by honey bees is known as propolis.

Propolis surrounds a honey bee nest.

In this photo of an open-air colony in Oregon, you can see the ring of propolis surrounding the nest. This ring provides a barrier to disease organisms. Photo © Naomi Price.

Plant exudates are vital to bee health

Feral honey bee cavities are often surrounded with rings of propolis to help deter pathogens, just as the entrance holes of resin bee nests are coated with a glistening layer. Plants produce these resins to keep themselves healthy. When a plant is injured, the resins ooze out of the wound, and the sticky consistency along with the antimicrobial components allow the plant to heal. By borrowing some of this sticky goo, the bees add layers of protection to their homes. Although it’s easy to remember that bees depend on plants for nectar and pollen, we sometimes forget they also raid the plant medicine chest.

If you mention propolis to a beekeeper, you can expect a groan. It’s messy, stains your clothes, cements bee boxes together, and won’t come off your hands. It destroys the look of comb honey and must be scraped, cracked, or otherwise dealt with. Unfortunately, early bee breeders spent a long time selecting for bees that collected little propolis. They believed beekeeping would be much easier if they could breed a bee that didn’t collect the stuff. But modern researchers are finding that propolis is vital to colony health no matter how inconvenient it may seem to the beekeeper.

Propolis is carried in pollen baskets

Honey bees carry plant resins in their pollen baskets. © Robert Lunsford.

In a recent article entitiled, “Darwinian Beekeeping: An Evolutionary Approach to Apiculture” (American Bee Journal, March 2017), Thomas Seeley suggests that beekeepers build bee boxes of rough-sawn lumber because the irregular interior surface will encourage propolis deposition. These deposits, Seeley says, will enhance the health of the colony by providing “antimicrobial envelopes.” Other researchers, too, are beginning to re-assess the role of propolis in honey bee health.

Resin bees become confused by the modern world

Bellflower resin bee

The bellflower resin bee, Megachile campanulae, has been known to collect artificial materials in place of resin. USGS public domain photo.

Normally you don’t hear much about resin bees, but one species made the news back in 2013. Megachile campanulae, more frequently called the bellflower resin bee, lives in the northeastern US and parts of Canada. Researchers discovered that some urban populations of these bees were collecting man-made materials, such as builders’ caulk, to use in place of resin. This is believed to be adaptive behavior compelled by urbanization: when the proper plant materials become scarce, the bees find alternatives. Unfortunately, the chemical polymers in caulk are not good for bees.

Although I have not heard of it, I wouldn’t be surprised to find honey bees collecting similar materials. Since we know honey bees collect sawdust and coffee grounds when pollen is scarce, it doesn’t seem far fetched that they might look for resin substitutes as well.

Glued together through time

As you can see, resin is a common feature in the bee world. To me, the existence of resin collection in multiple species is a strong indicator of its evolutionary value. We should pay attention. Far from being a mere annoyance, resin may be a beekeeper’s best friend.

Honey Bee Suite

Bee with me . . .

The gorgeous photo of an orange-tailed resin bee sealing her nest was provided by Mark Berkery in Australia. Mark is a remarkable nature photographer who specializes in macro shots of insects. I’ve been following Mark’s blog and photos for about six years and I continue to be amazed by his work. He also writes about macro photography and every spring, just before bee season, I re-read his macro advice. If you want to awed by bug pics, be sure to take a look. You won’t be disappointed.

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  • Hymenoptera is the third-largest order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 species are recognized, with many more remaining to be described.

    Aculeata is a subclade of Hymenoptera. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger (thus, the group could be called “stinging wasps”, though the group also contains the ants and the bees). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom. Not all members of the group can sting; a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether.

    This group includes the bees and ants and all of the eusocial Hymenopterans. It is commonly believed that the possession of a venomous sting was one of the important features promoting the evolution of social behavior, as it confers a level of anti-predator defense rarely approached by other invertebrates.

  • I’ve had to recaulk 2 mobile homes after my bees striped all the caulking from around the door and windows. It was a mess just trying to open the lid and even worse getting the frames out. Another time the bees worked a oil well head same scenario.

  • Thanks for the article. Many of us who have raised mason bees have encountered resin bees. They are a charming bee, but when they “glue” together a bundle of tubes or a couple of grooved boards, the frustration is memorable — vexing. It is easy to conceive of them teaching curious humans about natural glue because, especially when unsought, their skills are unmatched –and ruinous.


      • How is it that I only see your question 18 months later, following a link from another post of yours? (“Bee love: sealed with a propolis kiss”, Sept 2018) But really it doesn’t matter, because I am clueless who my resin bee is. I only discover their work long after the fact, when I try (and often fail) to open some firmly glued structure. By evidence they are small and a bit sneaky, and I’ve never seen one either enter or emerge.

        For a while I placed out reusable grooved boards sized 1/4″ holes for leafcutter bees, and regularly got resin bees – regular enough that I stopped setting out the block despite my fondness for leafcutters. Before that, when I still used bundled cardboard tubes for my osmia, I’d get resin bees using the gaps between the straws.

        • Glen,

          It takes 18 months because you’re not clicking “Notify me” at the end of your comment. Try it!

          The resin bees I’ve been able to identify here are Heriades. They are small, black, and inconspicuous but easy to i.d. to genus with a good photo.

  • Hi Rusty, Is it a detriment to the hive then to use a propolis screen and collect the propolis from the hive?

    • Donna,

      In my opinion, whenever you take something from a colony, it is a detriment to the colony. It doesn’t matter if you take honey, propolis, brood, bees, wax or anything else. The colony collected or produced those things for their benefit and survival, not yours, and they wouldn’t produce them if they didn’t think they needed them. So it’s up to the beekeeper to be prudent and observant about taking whatever he takes. It’s like taxation: the government can take a certain amount from your paycheck and you keep going. But if they took too much, the system would collapse and the government would have no one to tax the next year.

  • Mark Berkery’s photo is the best I’ve seen of head and neck anatomy! Thank you.

  • Hi Rusty,

    Numerous articles recommend encouraging honey bees to produce excess propolis by “roughing up” the interior of the hive parts, but I have not found further descriptions of how to actually do this. Any suggestions?

    I try to leave propolis inside the hive where I find it. Does it accumulate toxins like wax?

    • Margaret,

      I don’t know how people roughen the interior. Would a coarse grit sandpaper make it rough enough, or does it need to be gouged? Maybe someone else can answer.

      Toxins accumulate more easily in oil- or wax-based materials than water-based materials because of the way the chemicals are prepared. So I would suspect that there are some toxins in propolis, depending on the plants where it came from. I think generally, conifers are not treated as aggressively as field crops, but there is some background level of pesticides they probably pick up. I’m speculating here, but I assume the level is greatly less than the levels found in beeswax.

  • Thanks for this lovely article Rusty. There was some work done back in the 70s or 80s on the Apis mellifera colonies in Hawaii. The bees didn’t have access to the conifers that produce the typical resins, but the bees quickly found new sources of resin that had the same antibacterial, antifungal properties of traditional propolis. In S. America the bees collect both red and green propolis. The animal world seems highly adept at self-medication. I personally love the smell of propolis and tend to select from colonies that build a large curtain of propolis at the hive entrance, as those colonies winter well for me.

  • I wanted you to know that I found four resin-covered holes in an old drilled hole wood bee condo this week. When I did a search for resin and mason bees your articles were at the top of the list!

    The end caps on at least two of them is just resin and they have no mud cover as in your example. Heriades was suggested as the owner of my condo but I will have to try to spot them next year to find out for sure (and upgrade their space by providing a longer tubed home to boot). August Jackson suggested Douglas fir as the resource. I noticed that my sunflowers are also very sticky but he did not know if bees use that too.

    • Lisa,

      I too have small resin-covered holes in my bee boxes without any mud. I think mud and gravel are optional, depending on the species.

  • In 2017 my wife and I owned a farm in Central Michigan and had honey bees swarm our Eastern Pine trees one evening to collect the resin. It was a bit scary at first to hear the intensive hum, but awesome to watch. The collecting lasted until sunset and we never saw or heard from them again.

    • Phil,

      That’s interesting. I’ve seen large numbers of honey bees in our Alaska cedars at times, scraping up the resin. It’s fun to watch.