Goofy Bees

Nature can be incredibly complex and difficult to understand.  Every creature is always reacting to the conditions around them, and continually evolving strategies to keep up with an ever-changing world.  Because we don’t always understand the full spectrum of challenges facing organisms their behavior sometimes seems illogical.  (And, sometimes, it probably is.)  Regardless, trying to understand that behavior sure makes ecology fun!

Over the last month, I’ve seen two behaviors that are really interesting but don’t quite make sense to me.  Both involve bees.

On several occasions during the last several weeks, I’ve seen bumblebees spread out across the prairie, sitting on prominent high perches.  When approached, the bees fly a short distance and then either return to the same perch or land on a nearby one.  The second time I saw this, Anne Stine (Hubbard Fellow) and I were out collecting data for a research project.  There were dozens of bees on perches, and I just had to know what was going on.  Fortunately, I was able to catch Mike Arduser by cell phone and ask him.

A male bumblebee (Bombus griseocollis) scans for females.  Platte River Prairies, Nebraska.

A male bumblebee (Bombus griseocollis) sits above the prairie on an unopened stiff goldenrod flower. Platte River Prairies, Nebraska.

I didn’t even finish my description of what we were seeing before Mike was able to tell me the species and gender of the bumblebees, as well as the reason for their perching behavior.  He said we were seeing males of the species Bombus griseocollis, and they were on the lookout for new queens making their first foray from of the nests they were raised in.  Sure enough, a few minutes later, we saw a gigantic female bumblebee being swarmed by eight or ten smaller males trying to mate with her.   Apparently, the perching behavior is successful.

So I guess sitting on perches makes sense.  However, wouldn’t it be more effective for the bees to wait right outside the nest exit instead of at apparently random locations across the prairie?  Surely these bees – or at least some of them – hatched from the same nest as the queens, so they should know where that nest is.  I’d think the males would want to be as close to that exit as possible so they could be the first one to “welcome” the female to the outside world.  Maybe there’s a good reason not to do that, but I don’t know what it would be.  As I said earlier, this kind of thing is what makes ecology fun!

(Another thing that’s fun is tossing small flower heads or other bumblebee-sized objects near the perched bees and watching them dart out after them…)


The second bee observation came from the little prairie across town from my house.  I was out on a dewy morning, taking a few photographs before heading to the office.  It was cool and wet enough that most insects I saw were sitting very still, encased in droplets of water – a very nice situation for a photographer.

Many of those insects had found relatively sheltered and hidden locations in which to spend the night. A few, though, were right out in the open – something that seemed foolish to me, but certainly made it easier to photograph them.  One such insect that caught my eye was a medium-sized bee hanging upside down on a grass stem.  As I approached it, the bee spread its legs out (defense mechanism?) and by the time I set up my tripod to photograph it, the bee looked like a circus acrobat – hanging upside down and holding on only with its teeth (mandibles).

A female bee (Anthophora walshii) clings upside down to a grass stem with her mandibles.

A female bee (Anthophora walshii) clings upside down to a grass stem with her mandibles.  Lincoln Creek Prairie – Aurora, Nebraska.

I don’t even know where to start as I question this behavior.  First, why would the bee spend the night out in the open, rather than in a more sheltered location?  One explanation, I guess, is that it fears predators that hang out in sheltered locations than those that hunt in the open.  More confusing, however, is that this bee is a female ground-nesting bee.  She should have nearby a nest tunnel with eggs in it – why doesn’t she stay in that and protect her babies?  I asked Mike about this (of course) and he suggested it was possible that she had just become an adult and hadn’t yet had time to build her own nest.  I saw two or three other females of the same species nearby –  had they also just emerged as new adults from the same nest?  I guess it’s possible.

Another view of the same bee.

Another view of the same bee.

So, maybe the bee was a young female, still in the process of trying to find a good spot to dig her own nest tunnel.   I can buy that, and I wish her good luck if that’s the case.  However, that still doesn’t explain why she was hanging upside down by her mandibles…  I’m sure there’s a good explanation for that too, but I’m not sure I’ll ever figure it out.

Fortunately, my lack of understanding doesn’t make it less interesting to watch bees – and all the other organisms in the prairie.  In fact, quite the opposite is true.  If I knew what I was going to see – and why it was happening – there’d be no reason to go to the prairie at all!

Thanks (again) to Mike Arduser for confirming the identifications of these bees and for explaining at least some of their behavior!

Butterfly Aggression

We started seeing our first regal fritillary butterflies of the season last week, and began our second year of data collection on their habitat use in the Platte River Prairies.  As always, male fritillaries have emerged first and now have to wait a couple more weeks before females arrive on the scene.  In the meantime, they do some nectaring, but mostly seem to just fly around.  They look like a bunch of teenage boys who arrived at the school dance before the girls…

A regal fritillary butterfly seen last week in the Platte River Prairies, Nebraska.

The above regal fritillary was nectaring on a plant that will remain a mystery until my next post (sorry).  I was expecting to see them nectaring on common and showy milkweeds (Asclepias syriaca and A. speciosa) because those plants were just starting to bloom.  In some studies of regal fritillaries, milkweeds are major nectar plants.  Last year we saw regal fritillaries using hoary vervain (Verbena stricta) more than anything else, but I didn’t see a lot of milkweed blooming last year – for some reason.  This year, I figured maybe we’d see something different since milkweeds seem to be having a good year.

As I walked around checking milkweed flowers for butterflies, I saw a number of insect species using them, but none more abundant than the gray copper butterfly.  In fact, I saw one flower that had six coppers on it at the same time.

A gray copper butterfly on showy milkweed. The Nature Conservancy's Platte River Prairies, Nebraska.

I did see a few regal fritillaries nectaring on milkweeds, but surprisingly few, given the high numbers of both fritillaries and milkweeds I was seeing.  Eventually, I decided to just sit for a few minutes in front of one milkweed plant to watch the gray copper butterfly that was nectaring on it.  I figured I’d get to see a parade of other insects come by and nectar there as well.

I saw a fritillary making its way toward the flower and got my camera ready so that I could capture both the fritillary and the copper on the same flower.  However, when the fritillary got within a few feet of the flower, the copper suddenly erupted off the flower and flew straight at the fritillary, chasing it like a small bird chases a hawk.  The fritillary swerved off and sped away.  I saw the same thing happen twice more within the next several minutes.

What looks like a peaceful scene with a pretty butterfly nectaring on a flower belies the bottled up aggression waiting to boil over when another butterfly strays too close...

Throughout the day, I saw the same aggressive behavior by coppers on other milkweeds as well.  It’s hard to say, of course, whether the coppers were really protecting their nectar source, but that’s what it looked like to me.  There has been considerable discussion in the scientific literature about whether or not male butterflies (of some species) defend territories like birds do – keeping other males away.  There seems to be consensus that at least a few species do.

What I was seeing, though, was not mating territory defense.  Assuming that coppers can recognize the difference between their own and other butterfly species, they didn’t appear to be chasing away potential competitors for mates.  Instead, they appeared to be monopolizing a valuable food source.  Even when there were multiple milkweed flowers on a plant, or several plants in a clump, coppers successfully chased fritillaries away as they approached.  Interestingly, while coppers wouldn’t tolerate fritillaries, they didnm’t seem to mind sharing flowers with other coppers…  There weren’t many individuals of other butterfly species around, so I didn’t get a good feel for whether coppers chased away all other butterflies or just fritillaries.

I’ve not seen or heard of this kind of behavior before, but I’m sure other people have.  I’d sure appreciate hearing from you if you know anything about it.

Aggressive butterflies… who’d have thought?