Thursday, July 16, 2015

Giant Resin Bees

     Giant Resin Bees (Megachile sculpturalis), perhaps better called Sculptured Resin Bees since there are bigger ones in the world, are quite active this time of year. The largest Megachilid bees in North America, they're not supposed to be part of our landscape. They can reach an inch long, particularly the larger females, and are among the largest of any bees in our region. Megachilids such as Mason, Leaf-cutter, Carder bees, and their allies mostly carry their pollen on modified "hairs" (setae) on their bellies as opposed to the pollen baskets on the hind legs of many other bee families.  

Two Giant Resin Bees facing off. You can see the pollen on the "scopa" or pollen hairs on the belly of the lower one. They actively compete with each other, even stealing each others resin.

     Giant Resin Bees are native to Japan and other parts of Asia. They first appeared in North Carolina in 1994 and have since spread throughout most of the South and into Canada. They have also now been introduced into Europe, having been captured in France and Italy in 2008. What affect they have on native bees, other pollinators, and plants still needs to be confirmed, but they certainly compete for similar resources at least. It appears that despite their large jaws, Sculptured Resin Bees do not actually excavate very much or make their own holes. So they use cavities and holes they find, often competing with other creatures who also need them. This is especially true with Carpenter Bees, with the Resin Bees often using their old holes and perhaps keeping the Carpenter Bees from then using the burrows later on when they need them. Some claim the resins the bees use can harm or even kill Carpenter Bees. Others have reported that they attack other bees, even killing Honey Bees. 

A Giant Resin Bee takes over a Carpenter Bee hole.

     I myself have noticed them using Mason Bee boxes and tubes that I've put out. Luckily almost all the Mason Bees have completed their active life cycle by mid summer when these exotic bees emerge and become active. The Mason Bees are nestled in sealed tubes by then. But I've seen Sculptured Resin Bees trying to make use of the empty holes and tubes, which are then not available the next spring for Mason Bees, or the Leaf-cutters that sometimes also utilize them. More disturbingly, I have often found the paper tube inserts or tubes themselves (both empty and those with sealed Mason Bee larvae) either completely pulled out or half way pulled out of the boxes with Giant Resin Bees then utilizing the now-larger holes. I've never caught one actually pulling them out (though I've seen them mouthing them), but I think it's perhaps more than a coincidence.

Two Sculptured Resin Bees seal their own tubes and provision others in a Mason Bee box. Some tubes are still empty and available and some have had their paper inserts removed. 

     Like most members of the Megachilidae family, both males and females visit and pollinate flowers. These are solitary bees, with each female choosing a hole or cavity to set-up housekeeping. With no queens, workers, or guards (like the vast majority of bees), she takes on every role by herself. Sometimes many females will utilize the same area or piece of wood if the location or situation is very favorable. Pollen is collected and mixed with nectar to make a ball of food that is deposited in the hole. After enough is collected, she lays a single egg and seals the cell, often with tree resin as well as mud and bark. She might complete up to 10 cells per hole or tube before sealing everything off again, often with an extra layer of resin.

A Giant Resin Bee egg attached to its food hoard at the end of a cell.

     When the eggs hatches, the developing bee larva feeds on these food stores throughout the summer. It will pupate and spend the winter in its cell before pupating and emerging in mid summer as an adult bee that then starts the cycle all over again.

A newly hatched Giant Resin bee larva on top of its food stores. 

An opened Mason Bee house that instead is full of various stages of developing Giant Resin Bees and their cells. 

     On the Capital Naturalist YouTube Channel you can see a video of Giant Resin Bees around an old shed. Please copy and paste if this link doesn't work for you: 
     Again, no one is sure if these exotic bees affect our native pollinators and especially our bees. It appears though that at minimum they compete for food and nesting sites, if they don't outright attack or kill other bees. That they are also one of the primary pollinators for Kudzu in their native lands is also unnerving, since this invasive plant certainly doesn't need any more help reproducing. Giant Sculptured Resin Bees have spread dramatically through both North America and Europe and may indeed be something to worry about. We shall see.


  1. Hi Alonso!
    I really appreciate you writing about these bees, as little is still known about them and I've had an experience that makes me feel they are unwelcomed predators to our other bees!

    My husband and I live in an old NYC apartment on a higher up floor, with old wooden windows that have been inhabited by carpenter bee families for years. We love our bees, and were deeply disturbed to find 3 carpenter bees - 1 dead, 2 barely alive, seemingly covered in a sticky substance and crawling around on the window sill. Later that day we saw a large wasp or bee-type insect hovering around the carpenter bee nests. My husband was able to catch it and we researched it for a while, determining without a doubt it was an Asian Resin Bee. It also had a ball of "resin" with it, which confirmed our suspicions.
    After reading a bit about these bees, we guessed that it must have evicted the poor carpenter bees from the nests, somehow covering them completely in the sticky resin. We tried our best saving them but to no avail, and it was very upsetting. Also, the next day we noticed a sticky (VERY sticky) substance dripping down our screen, from the carpenter bee hole, and strange pieces of yellow remnants on the sill below.
    We are afraid these introduced resin bees are wreaking havoc on other bees, and I would love it if there were more studies done, as our bees are quickly dwindling. I'm in the process of contacting someone in our area to come look at the nests.

    I'd love to hear your opinion on this!


  2. 2nd the pulling out of tubes by these bees. I had no issue with tubes till these guys took over after the leaf cutters then all of sudden the smaller diameter tubes would be pulled 1/2 out every few days.