Massachusetts bumblebees are in trouble

This follows a trend of declining bumblebees in the northeast US

There are about 50 species of bumblebee in the US and Canada, and over the last decade, it has been well documented that multiple species of bumblebee are declining. However, the picture is complicated, with some species declining, some increasing, and other species lack the data to know one way or the other. It also varies by region, since some declining bumblebees are still doing okay in certain areas of their range. As a result, bumblebees in some areas seem to be doing much better than others.

So how are bumblebees doing in Massachusetts?

Starting approximately 100 years ago, scientist Otto Plath (also notable for being the father of poet Sylvia Plath), conducted an in-depth investigation of the bumblebees of Massachusetts. Based at Harvard’s Arnold Arboretum, he excavated and studied hundreds of bumblebee nests and exhaustively documented the biology of the different species. He published his work in various scientific journals, and then finished with his magnum opus, the 1934 book “Bumblebees and Their Ways.”

As a result of that book, there is a fairly complete picture of how common different bumblebee species were in Massachusetts back in the period spanning 1921 to 1933, when Plath did most of his research. This research can be used to see how the historic bumblebees compare to the present day. From that record, one thing is clear — Massachusetts bumblebees have undergone some big changes, and they’re mostly bad.

The Rusty-patched bumblebee (Bombus affinis) used to be common in Massachusetts but not it no longer occurs in the state.

In total, Otto Plath documented 13 different bumblebee species in the vicinity of Boston. By comparing them to more than 8000 recent observations on the community science platform iNaturalist, we can get a rough idea of how they’ve changed, particularly whether any of the species he reported are no longer around, or if species that were previously common have become rare.

Here are how the 13 species Plath documented are doing now:

1. Bombus affinis, the Rusty patched bumble bee. Status: Extremely Bad. Plath reported this to be one of the more abundant bumblebees, describing it as a “common” species and he reported finding 66 nests. In recent times, the rusty patched bumblebee has experienced precipitous declines and no longer occurs in Massachusetts. Instead, it is restricted to a relatively small pocket of its former range in the midwestern United States and it has the dubious distinction of being the first bee in the continental United States to gain endangered species status.
2. Bombus bimaculatus, the Two-spotted bumble bee. Status: Good. Plath referred to this species as a “common Eastern species” and reported finding 37 nests. In the present day, Bombus bimaculatus is the third most commonly observed species in Massachusetts, suggesting that it hasn’t undergone major changes.
3. Bombus borealis, the Northern amber bumble bee. Status: NA — not enough information to draw conclusions. This primarily northern species has apparently always been rare in Massachusetts, with Plath reporting that he had seen “only seven living specimens.” It is also rare in Massachusetts in the present day, with just a few observation of this species in the western part of the state reported on iNaturalist. This suggests there haven’t been major changes but there’s not enough information to know for sure.
4. Bombus fervidus, the Golden northern bumble bee. Status: Declined. This species is still present in Massachusetts, but it appears to be much less common than in Plath’s time. Plath referred to this as a “common American species” and reported finding 49 nests. In contrast, present-day observations on iNaturalist show this species to be present but relatively uncommon.
5. Bombus griseocollis, the Brown-belted bumble bee. Status: Increased. This species is common across the United States, and Massachusetts is no exception. Indeed, Bombus griseocollis comes in as the second most commonly observed MA bumblebee on iNaturalist. However, Plath reported this bee as much less common in his time, stating that the bee was “rather common in the Southern and Middle Western States, but comparatively rare in the vicinity of Boston.” Further, Plath only found three nests of this species, supporting the idea that it was rare, at least in eastern MA. Overall it seems clear that this bee has increased markedly in relative abundance.
6. Bombus impatiens, the Common eastern bumble bee. Status: Increased. This bee is by far the most common bumblebee in Massachusetts, with more than 3 times the number of sightings of the second most common bumble (Bombus griseocollis) and more than 10 times the observations of the third most common bumble (Bombus bimaculatus). Bombus impatiens appears to be increasing in relative abundance across most of its range, and it has even spread to the west coast from bees that escaped from managed colonies being used for greenhouse pollination.
7. Bombus pensylvanicus, the American bumble bee. Status: No longer occurs in MA. This species used to be one of the most common bumblebees in the US but it has declined in many areas of its range. Recently, it was petitioned for endangered species status. However, Bombus pensylvanicus was never common in Massachusetts, with Plath calling it “comparatively rare.” Nonetheless, with no iNaturalist records in MA, this species has likely been lost from this part of its historic range.
8. Bombus perplexus, the Perplexing bumble bee. Status: Good. Plath called this species “comparatively rare” and only discovered 5 nests. On iNaturalist, it is currently the fourth most sighted species, so it seems like this species could have potentially increased compared to 100 years ago.
9. Bombus ternarius, the Tricolored bumble bee. Status: Unchanged. Plath reported this species as “exceedingly rare in the vicinity of Boston” and that situation appears to be unchanged. Though with only a handful of records from eastern MA, this species is potentially declining.
10. Bombus terricola, the Yellow-banded bumble bee. Status: Declined. This is another bee that has experienced widespread declines and it’s doing poorly in MA. Plath said it was “somewhat less common in the vicinity of Boston than Bombus affinis” and reported finding 20 nests of this species. In the current day, Bombus terricola does not appear to occur in eastern MA anymore. Instead there are only about a dozen records in western MA.
11. Bombus vagans, the Half-black bumble bee. Status: NA — not enough information to draw conclusions. Plath reported Bombus vagans as “fairly common” and found 20 nests, but it’s difficult to know how this species is doing because it is difficult to accurately identify from photos. This is because another species, Bombus sandersoni, that can have an identical color pattern, and it can also look similar to Bombus perplexus. As a result, many photos that are likely Bombus vagans are unable to be identified.
12. Bombus ashtoni, Ashton’s cuckoo bumble bee. Status: Terrible. This is another species that has undergone drastic declines. Bombus ashtoni is a cuckoo bumblebee, meaning it invades other bumblebee nests and has them raise its young. The hosts for Bombus ashtoni include Bombus affinis and Bombus terricola, which have both declined. Plath found 13 colonies with Bombus ashtoni in the vicinity of Boston but there are not recent records from Massachusetts. In eastern North America, there are just a handful of recent sightings of Bombus ashtoni in Maine and Quebec, so it is extremely unlikely that it still occurs in MA.
13. Bombus citrinus, the Lemon cuckoo bumble bee. Status: Declined. Plath called this bee the “most common [cuckoo bumblebee] in the vicinity of Boston” but there is currently just 1 record of this species on iNaturalist in MA. This is odd because the primary host of Bombus citrinus is thought to be Bombus impatiens, which has increased in relative abundance. You would expect the fortunes of the cuckoo to rise with their host, but that isn’t the case, and it’s not clear why.

Overall, out of the 13 bumblebee species that Plath reported as occurring in the vicinity of Boston, 3 no longer occur in Massachusetts, 3 more have clearly declined, 3 seem about the same, 2 have increased, and 2 have insufficient information.

Clear declines in 6/13 species is rather worrisome. Before looking into this, I didn’t expect the results to be that bad. Worse, these results are in line with other studies from New England. For example, a 2018 study by researchers at the University of Vermont looked at historic records of 17 Vermont bumblebees and could not find 4 in the state and found another 4 that had clearly declined. Similarly, a 2017 study by researchers at the University of New Hampshire looked at 13 species of New Hampshire bumblebees and found a “drastic decline” in 3 species and a “significant decline” in 1 species. Overall, we see declines of 6/13 species in MA, 8/17 species in VT, and 4/13 species in NH. Three species in particular — Bombus affinis, Bombus fervidus, and Bombus terricola — have declined in all three states and other areas of their range as well.

The Lemon cuckoo bumble bee, (Bombus citrinus) has declined in Massachusetts.

It’s possible that iNaturalist observations may be missing some species that do actually occur, but the similar findings by more rigorous scientific analyses in neighboring states suggests that what we see on iNaturalist is a good representation of the species that are present. While it would be good to confirm the Massachusetts results with a more complete analysis using specimens in museums and natural history collections, the changes over the last 100 years are so dramatic that many of the trends are already clear.

One of the most worrying aspects of these bee declines is that scientists have been largely unable to pinpoint the cause. It’s thought that an introduced disease played a role in the decline of at least some species, but so far research has been inconclusive.

The combined pressure of multiple factors plays a role in bee declines, including disease, pesticide use, lack of flowers, habitat loss, climate change, and competition with non-native honeybees. Unfortunately, that means saving these bumblebees will require major changes in how we manage and interact with our environment. Saving bumblebees will require massively reducing pesticides, preventing invasive pests and diseases, increasing native habitat, regulating managed honeybee and bumblebee colonies, and tackling climate change. Whether people are willing to tackle these big challenges is less clear. How many more bumblebee species does Massachusetts need to lose before taking action?