Check out this short video I made about the American bumblebee, a gorgeous gentle giant we saw somewhat frequently in our watermelon fields, pollinating watermelon flowers, but also on the wildflowers we planted in those fields. Turn on the sound for my commentary.
The photos below show that we've seen both the males and females in our study. The males have never been seen visiting the watermelon, only the wildflowers and most commonly on the Zinnia elegans. The males do not collect pollen like the females do, so they are probably sipping nectar from these flowers for their own survival. The females have corbicula, or pollen baskets, on their hind legs where they store the pollen they collect on their foraging trips, mixed with a bit of nectar to allow it to stick together and not fall apart in flight. It basically forms this big ball of pollen on their hind leg that becomes quite visible the larger it gets and the more pollen the bee collects. Honey bees are the only other bees that have these corbicula, and you can also see them quite frequently with a big ball of yellow or white pollen on their legs. The corbicula is basically a widening of one segment of their hind legs, with little to no hairs except for these large curved bristles on the edge of this segment that sort of keep the pollen ball together in place. Other bees will have other places on their body where they have special scopa or pollen-collecting hairs, or they may just have extremely dense and feathery hairs on their legs to collect pollen. It is interesting how they have adapted and evolved different ways to do the same sort of thing--except of course that some bees will collect from different types of flowers with different pollen that is unique and some bees collect floral oils, etc. Remember that there are 20,000 species of bees in the world--and that's just the ones we have described and know about--they are certainly many many more we have discovered yet.
Anyway, the American bumblebee male looks quite different than the female, as you can see below. The male has golden/yellow hairs all the way down his abdomen to the tip or almost the tip (he basically has a golden butt). The female bee only has yellow hairs on her abdomen until about halfway down the abdomen, with black hairs the rest of the way to the tip (technically the female has yellow hair on abdominal segments 1-3 if you're insect taxonomy-savvy). The females have a thorax (the body part between the head and abdomen) that is basically yellow near the head and the rest black. Her head is long and narrow compared to some bumble bees with a fatter head, with a long malar space or "cheek" as they would describe in taxonomic keys. That would be the basics of id'ing these beauties in the field, in addition to looking up their geographic range to see the likelihood that they are even in your area.
They are considered "vulnerable" by the IUCN and have experienced huge decreases in their geographic range, which use to span much of N America, including Mexico. Apparently it is mostly their northern range which has been reduced, although even in southern states the historical records show somewhat of a decline. One study found them to be one of the most sharply-declining species in N America, and is only found in 34% of its previously sampled US and Canada range (Colla et al 2012*). I am always happy to see them in my fields and know that our pesticide-free wildflowers are providing them much needed nutrients. They are commonly found in open grasslands and agricultural areas, and tend to nest above the ground in tufts of long grasses, thus are particularly susceptible to grassland habitat loss, intensive agriculture land-use, and management activities that neglect their nesting requirements (Hatfield et al 2012**).
male on Zinnia elegans
male on Zinnia elegans
female on Chamaecrista fasciculata
female on Zinnia elegans
female on watermelon
*Colla, S.R., Gadallah, F., Richardson, L., Wagner, D. and Gall, L. 2012. Assessing the Conservation Status of North American bumble bees using museum records. Biodiversity and Conservation 21: 3585-3595.
** Hatfield, R., Jepsen, S., Mader, E., Black, S.H. and Shepherd, M. 2012. Conserving Bumble Bees. Guidelines for Creating and Managing Habitat for America's Declining Pollinators. The Xerces Society for Invertebrate Conservation., Portland, OR