Progress on Bumblebees

by Carl Strang

Earlier I posted some background on bumblebees . I find that I made an error or two there, I since have found additional species at Mayslake Forest Preserve, and also some added web sites specific to Illinois bumblebees that have helped immensely. The total list for Mayslake at this point includes 5 species, and I showed a photo from Fullersburg Woods of a 6th, Bombus vagans, in that earlier post. There are 9 species total for Illinois, of which 2 are rare. (Here I am not counting the nest-parasite “cuckoo bumblebees,” of which there are 2, but which I have not yet encountered). To this point in the season, the most common species has been Bombus bimaculatus, both at Mayslake and in my garden at home. It has a yellow thorax except for a black dot on top, the first (basal) abdominal segment is yellow, the second segment is yellow in the center front edge but black on the ends and back edge. Otherwise the abdomen is black.

Bombus bimaculatus 2b

The patch of yellow on the second segment often is small and hidden by the wings, so care is needed to distinguish bimaculatus from another common species (though perhaps less common locally than I implied in that earlier post), Bombus impatiens. The main difference from bimaculatus is that the yellow on impatiens’ abdomen is confined to the first segment.

Bombus impatiens queen 2b

One correction I need to make to that earlier post is that the dead bumblebee I featured was not Bombus fervidus after all. That bee had a black basal abdominal segment, where in fervidus the first 4 segments all are yellow. I have found a few live members of the dead bee’s species at Mayslake.

Bombus auricomus 10b

This is Bombus auricomus, which is regarded as “uncommon” in Illinois. Here, the first segment is entirely black, segments 2 and 3 entirely yellow. The sides of the thorax are black, and as the next photo shows, there is a large black area in the center of the dorsal (top) thorax.

Bombus auricomus 2b

At Mayslake I have seen only a few of these, always in the same place, so I believe there is only one colony of them on the preserve. Compared to other bumblebees they are large and very active. Bombus fervidus is at Mayslake, too.

Bombus fervidus 3b

Here you can see that the basal segment also is yellow, as is the entire thorax except for a black band across the back between the wings. In that earlier post I mentioned the ecological significance of differences in tongue lengths among species. Get a load of the tongue length on that fervidus!

Bombus fervidus tongue b

The 5th Mayslake species to date is Bombus griseocollis.

Bombus griseocollis swamp milkweed 3b

In this one the forward edge of the second abdominal segment is orange, but the back edge is black. The color on the second segment extends closer to the edge than it did in bimaculatus.

Bombus vagans, which I have seen at Fullersburg but not yet at Mayslake, has the first two abdominal segments yellow all the way to the back edge.

Bombus vagans 1b

That leaves only one species of bumblebee which is said to be common in Illinois but which I have not yet observed: Bombus pensylvanicus (listed in some references as B. americanorum). That one is most similar to B. auricomus, but typically has the top rear part of the thorax black or orange, and the first abdominal segment has some yellow on its rear edge.

Here are some web references. For a really nice diagrammatic comparison of these color patterns you can download a pdf file called “Bumble Bees of Illinois and Missouri”. A site with additional identification and ecological information is the beespotter site.

Bumblebees

by Carl Strang

Bumblebees are fascinating insects, and I have much to learn about them. So far I slowly am getting a handle on some of the local species. It happens that they are generally easy to distinguish through their different arrangements of yellow and black fur. I call it fur; it certainly holds in heat generated by their flight muscles, allowing them to range through temperate climates into the Arctic. I remember seeing bumblebees on my study area in western Alaska. In our area the most common species may be Bombus impatiens. Here is a queen of that species.

Bombus impatiens queen 2b

Bombus impatiens is marked by the thorax being almost entirely yellow, especially on the sides, and by the black abdomen with only the first segment yellow. The queens are all you see early in the season. Only they survived the winter. By June their much smaller daughters are visiting flowers. I suspect this may be why Solomon’s seal (mentioned yesterday) waits to bloom until now. The tiny faces of bumblebee workers just fit in the suspended flowers of that species. I doubt that a queen could manage it.

Ecological studies of bumblebees emphasize tongue length, with different species subdividing the range of flower sizes accordingly. B. impatiens, being a generalist, has an intermediate tongue length. As I get a handle on the species I will want to learn about this difference and see which bumblebees visit which local flowers. Here is Bombus vagans, which I photographed visiting wingstem at Fullersburg a couple years ago.

Bombus vagans 1b

Note that it has two yellow abdominal segments. It also is larger than impatiens. The next shot illustrates the significance of tongue length.

Bombus vagans 2b

A third species is Bombus fervidus. This one I haven’t caught in action. The photo is of a dead one I found on the trail at Tri-County State Park.

Bombus fervidus 3b

Note the large black area on the thorax and the mostly yellow abdomen. I have seen it at Mayslake, as well. In recent days the picture has become a little clouded as I have found another species at Mayslake that is very close to impatiens, and so needs close study to distinguish it.

Bombus bimaculatus 2b

Bombus bimaculatus has the first abdominal segment yellow plus the central part of the second segment. The feet are yellow, as is a tuft of hairs on the top of the head, barely visible in the next photo.

Bombus bimaculatus 3b

Those last minute features help distinguish it from another species, B. griseocollis, which I have yet to find.

Here is a website with a key to bumblebees of Wisconsin, which I have found helpful in making identifications.

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