5 weird and wonderful facts

This year the Native Pollinator Initiative team started a new bumble bee research project, where the field team built, installed, monitored, and removed a suite of bumble bee artificial domiciles throughout Ontario from March to October. The wooden nest boxes have been used extensively in research elsewhere in the country but had not yet been thoroughly tested with our Ontario native bumble bees, so we had a lot of questions… will Ontario bumble bees even want to live in artificial nest boxes at all? Will we be able to use these boxes to attract rare bumble bee species like the yellow-banded bumble bee or the rusty-patched bumble bee? What sorts of common bumble bee species might like to use these boxes, and why? What nest box installation methods will work best in this province?

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196 boxes were placed at 15 different sites from Norfolk County to Sudbury, and each site had 14 vacant humble (bumble) abodes set up in 2 different ways – dug underground to mimic abandoned rodent burrows or attached to trees to mimic tree cavities, two favourite nesting places for these important pollinators. Our main goal with this project was to investigate the use of nest boxes for bumble bee conservation, but we learned a lot more about bumble bee nesting ecology along the way!

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Fact #1: Nest Defenders

Bumble bee colonies are made up of 3 different types of bee, or “castes”. Most people know of the queen bee, the worker bees, and the male bees or “drones”. However, what you might not have known is that sometimes individual worker bees can be assigned different jobs within the colony. Some workers might be in charge of cleanup crew – removing dead bees from inside the colony or secreting wax to patch up degrading colony structures, some workers might be responsible for foraging to collect nectar and pollen to feed the growing colony… and some workers are assigned to guard duty! Often when we went to check up on the nest boxes, our first sign that there was a colony growing within them was a cute little bee face peeking out at us from just inside the doorway, keeping a watch out for predators. These guard bees often just sit at the colony entrance, making sure that no one that doesn’t belong tries to invade, and sometimes they might even come out and hover around the entrance if they sense a greater threat.

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Fact #2: How bees beat the heat

We visited one of our sites on an exceptionally sweltering day in July. The air was still, and the heat was seemingly impenetrable… us field biologists were all wishing we had brought some sort of portable fan to cool ourselves as we sweated through our field clothes. Before that day, we hadn’t really considered how bumble bees handle the heat – it can’t be easy being a bee in 40 degrees, given their furry exterior… especially for some of our colonies that nested in tree boxes and were exposed to direct sunlight. Wax, obviously, can melt… and furry bodies are meant to be insulated against the cold!

When we arrived at a colony that was out in the open, we were surprised to see a few workers gathered at the entrance of the colony. As we got closer, we realized what they were doing… fanning their colony to keep it cool! This is a common behaviour for bumble bees when their queen ends up making a suboptimal choice in housing location, leaving them directly exposed to the sun’s rays on a hot summer’s day. Avoiding too much sun exposure may not be at the top of a queen bee’s list of requirements when she is choosing where to live in the cool of early spring.

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Fact #3: Bathroom break

As we were checking on nest boxes through the summer, trying to tell whether or not there were bee colonies residing within them, some were definitely easier to detect than others. Approaching a colony, squinting from afar, sometimes we noticed a distinct… decoration… on the front of a nest box. Yellow spatters spraying out from the entrance indicate – you guessed it – that the bees had been sticking their little butts outside of the colonies to relieve themselves right on the doorstep! Though this may initially come across as a bit rude, it actually indicates that the bees are trying to maintain cleanliness inside the box, where all of the colony structure, stored food, and baby bees (larvae and pupae) reside. Bumble bees will usually try to avoid defecating and urinating directly inside the colony, and what better way to make an artistic statement than to embellish the entrance of their home with a lovely spray of yellow bee poop.

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Fact #4: Unexpected neighbours

We were surprised and interested to find, both when we checked on boxes during the summer and when we collected our boxes in the fall, that bumble bees weren’t the only creatures that revered the new real estate! Often boxes that didn’t have bumble bees in them were full of ear wigs, ant colonies, centipedes… and a few other more surprising tenants…

We also discovered that even if a bumble bee queen took a liking to a box and started a colony in it, that didn’t necessarily signal to other potential lodgers that it was occupied! While sorting through colonies at the end of the season, we unearthed some unexpected squatters – and some were better roommates than others…

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Fact #5: Mystery colonies

When we went out to check our boxes in mid-summer, we tried to avoid disturbing any of the potentially growing colonies, and so we didn’t actively open any tree boxes or unearth any underground boxes. We usually waited for a while to see if we noticed any buzzing activity, looked for evidence of bumble bee bathroom use outside the entrance, and checked for a guard bee hanging out in the doorway. After our summer inspections, we were a little disappointed by the low levels of occupancy that we detected – we only noticed 6 active colonies in total, out of 196 deployed boxes. However, when we returned in the late summer and early fall to start collecting the boxes, it seemed like at almost every site we visited… we were surprised by the discovery of colony after colony, unnoticed in the summer! In the end, we collected a total of 16 fully-grown bumble bee colonies. That means we missed detecting over half of our nests when we observed for activity earlier in the season!

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Fact #5: Mystery colonies cont’d

We have one theory as to why so many colonies were overlooked… different species of bumble bees have different timing of when queens emerge in the spring and when colonies peak and wind down in the summer and fall – this is referred to as a species’ “phenology”. Therefore, some of the colonies we checked on in July may have already completed most of their life cycle, and once a colony starts producing reproductives instead of worker bees, there is a lot less activity at the colony as the queens and males disperse further away from home to find mates. Alternatively, certain species have a more advanced seasonal phenology, and during our visits, may not have yet hit their peak of production until later in the summer.

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What’s next?

Next year, to try to better detect when colonies start and finish, our former field biologist Hayley Tompkins is currently waiting in the wings. Hayley is starting her Master’s degree at the University of Guelph next year, and will be taking over the nest box research project – after participating during this pilot year. With her now keenly trained eye, she will be checking on the 2018 boxes more frequently through the spring and summer. She will make sure to take a closer look at every visit, so that she knows for certain whether there is a colony in a box or not.

We are looking forward to discovering more weird and wonderful things about bumble bees and how they nest in the years to come, and fingers crossed we are able to entice a species at risk – like our target bumble bee species, the yellow-banded bumble bee – to call one of our carefully crafted domiciles home during next year’s field season.