Thursday, October 27, 2016

Bumble Bees in our yard in Jonesboro, summer 2016

For a long time we have wanted to get interested in studying bees, but they are notoriously difficult to identify and there must be some 3000 species in the United States. But we decided if we started with one small, relatively easy to identify group, it might be a way in, and our friend Herschel Raney suggested we look at bumble bees this year, and they seemed perfect. So in 2016 we became seriously interested in the bumble bees that visited our garden. (We knew nothing at all about them.) We had a guide to identification (Bumble Bees of North America, Thorp et al.,[2014]), and as our first step we checked their distribution maps to see what species were possible in our area. Here is the list we came up with:

Bombus bimaculatus, the Two-spotted Bumble Bee
B. griseocollis, the Brown-belted Bumble Bee
B. vagans, the Half-black Bumble Bee
B. auricomus, the Black and Gold Bumble Bee
B. pensylvanicus, the American Bumble Bee
B. fraternus, the Southern Plains Bumble Bee
B. impatiens, the Common Eastern Bumble Bee
("pensylvanicus," by the way, is the correct spelling. It's just something that happens when you latinize a word.)

We had beds of flowers designed, over the years, in such a way that when one group of flowers finished blooming, another flower series would take over,  so that we had almost continuously blooming flowers. This was designed to attract butterflies, but it now also turned out to attract a continuously changing suite of bumble bees. By the time the first bumble bees showed up in early June, the pink phlox flowers were up, terrific for long-tongued moths and butterflies, but with their single deep narrow holes to the nectaries, they did not attract a single bumble bee. However, the pink coneflowers with their daisy-like flowers, each flower with an abundance of florets, and, in our pond, pickerelweed, with spikes of purple flowers, so that in each case a bumble bee could visit several nectaries by crawling around, without having to take off with its heavy body and land again, were both very attractive to bumble bees. At first we had mainly Bombus bimaculatus, Two-spotted Bumble Bees. I assumed the two black squares on the sides of the second abdominal segment were the source of the name, and these made the species easy to identify. ( I have recently read it is because of the two yellow spots, so now I’m not quite sure where I am.) Anyway, here is the Two-spotted Bumble Bee.

Most bumble bees are more or less alike, except with different patterns of black and yellow. So let's take this picture to orient ourselves, and see marks we need to see to identify the different species. Starting from the front, we see that this one has yellow at the top of the head. Some species have yellow at the top of the head, some have black. Next, we see that the thorax is completely yellow. Some species have a band of black over the top of the thorax, or black on the sides of the thorax. Different species have different segments of the abdomen black or yellow. On this species the belly is black, but the upper half of the first abdominal segment is yellow, and the second abdominal segment is yellow in the middle, but black along the sides, and then the remaining five segments (seven segments altogether) are black. Here it is now from the back:

The black spot is frequent in the center of the thorax on top. It is usually a sort of bald spot.

This was the first of the seven species we might see, and at first it was the only bumble bee around. It was particularly common on the dense bed of flowering pickerelweed in our pond. But occasionally we would see a Brown-belted Bumble Bee in the pink coneflowers out in the front yard.

This species similarly had yellow on top of the head and an all yellow thorax, and the first abdominal segment yellow. But the second segment was brown or at least brownish.

 And also occasionally we saw the Half-black Bumble Bee.

And once more, in this third of seven possible species, the top of the head was yellow, and the thorax was completely yellow. But in this case, the first two segments of the abdomen were more or less yellow, and the following segments were black, though with lengthy yellow fringes.

But with individuals with more modest fringes, it was easier to see why the species was called the Half-black Bumble Bee.

Then there was a change. The Two-spotted Bumble Bee became increasingly scarce, while a new species appeared. This one was very natty and quite different from the others. The front half of the thorax was yellow, the back half black, a broad black band pulled over the top. Two or three segments of the abdomen were yellow, then the last four formed a solidly black end.

This fit the pattern of B. auricomus, the Black and Gold Bumble Bee, and so that was what we called it, the fourth of our seven possibles.

Now the basket flowers were blooming out in the front yard, and we got a new species.

On this one, the back half of the thorax was black, the sides of the thorax were black, and all the segments of the abdomen were yellow, except the very last, which was dingy. Now we had a problem, because two species seemed to have that pattern, B. pensylvanicus, the American Bumble Bee, which was common everywhere, and B. fervidus, the Yellow Bumble Bee, which was common almost everywhere, though the range map did not quite touch our region. We went back and forth on this for quite a while until we remembered that other field mark. B. fervidus had yellow sides to the thorax, while pensylvanicus had black, and on ours we could see the black clearly. So pensylvanicus was the fifth of our seven possibles.

But then we found another problem. In the cup plants, also very popular with bumble bees, which were taking over from the fading basket flowers, we began seeing bumble bees marked like this:

This was the pattern of auricomus, the Black and Gold Bumble Bee, but something was not quite right. When we checked carefully through the descriptions of the various bumble bees, we discovered that pensylvanicus had an alternate pattern that looked exactly like this. This was confirmed for us when we were lucky enough to see a male pensylvanicus in the typical pattern mating with a female (a queen, that is to say) in this new pattern.

So these were pensylvanicus in a new pattern. But what about those first ones we saw? Were they Black and Gold? Alas, we remembered another field mark we needed to look at. The Black and Gold Bumble Bee has yellow on the top of the head; pensylvanicus has black, and that meant black in both of its color patterns. We checked all our photographs, and where the top of the head was at all visible, they were all black. We eliminated Black and Gold from our list, and now we were back to four of our seven possibles.

We felt much better however when, for one day only, we had a visit from a very handsome new species, Bombus fraternus, the Southern Plains Bumble Bee.

This one, in very clean black and pale yellow, had the first two segments of the abdomen pale, the rest black, and had a very slim black band over the back of the thorax just between the wings. So we now had five of the seven possible. We decided we weren't going to get Black and Gold, but we thought we were still likely to get the last one, B. impatiens, the Common Eastern Bumble Bee. We waited day after day for it to show up. The season was moving towards fall, however, and all of our seasonal flowers were coming to an end, and it didn't seem like any were left to come to serve as an attractant. Our scraggy weedy goldenrod plants, off in an untended corner of our yard, had not come out yet, but they didn't seem like they would draw in any bumble bees when they did.

That was the situation when we left to go to Arizona to see our brand new grandson.

Three weeks later we returned to find the goldenrod in full bloom and crawling with Bombus impatiens for a nice finish to the year, six out of the possible seven, not too bad for one garden.

B. impatiens (the name comes from the Latin name of a flower it particularly favors, jewelweed, though evidently goldenrod will work in a pinch) has yellow on top of the head, yellow thorax (with a particularly large bald spot), first segment of the abdomen yellow and the rest black.

I read now that the favorite habitat of B. auricomus, the Black and Gold, is not the garden, but open fields and farmland. That's where we will be looking for it next spring.