I apologize in advance for putting up an ARKive video that is self-starting (they all are from that site), but thank Ceiling Cat it is relatively silent. And it’s worth the watch.
I learned about this phenomenon from reading The Folly of Fools, Bob Trivers’s new book on deceit and self-deception, and have read the paper in Nature (reference below) that describes it. It’s a case in which a group of larval beetles work together to imitate a bee, fooling a real male bee into copulating with the mass of larvae, who then are transferred to female bees via real bee-to-bee copulation, and then taken to the female’s nest, where they spend the next stage of their life.
According to the paper by Hafernik and Saul-Gershenz, the larvae of the blister beetle Meloe franciscanus emerge from the sand in the Mojave Desert and immediately aggregate, crawling as a mass onto vegetation. They then form a bee-sized ball that “responded to outside stimuli, such as nearby movements, by waving their front legs or by contracting as a unit.”
You can see all this on the video below.
This moving ball of blister beetles beckons to male bees, who think it’s a female and try to copulate with it. That’s also on the video. The researchers watched 42 bees of the species Habropoda pallida approach the mass (this is a species of “solitary bee,” that is, they don’t nest communally, but a single female builds her own nest in the ground or in vegetation, and provisions the offspring with pollen rather than nectar.) All of these 42 bees were male. Nine of them tried to copulate with the mass, and when that happens a bunch of of beetle larvae climb onto the bee, temporarily debilitating it (see below).
The male bee falls to the ground and then grooms off most of the larvae—but he can’t remove the ones on his ventral service. (This is also true in the Drosophila I work with: when I dust them with fluorescent powder, they can groom all of it off except for some on their ventral side of the thorax.)
Now the male bee has a beetley venereal disease; in fact, every male has it: all the male bees that the authors sampled in one year carried beetle larvae.
The next problem is getting the larvae to females so they can be deposited in the nest. That’s essential because the beetle larvae eat the pollen that the female stores for her offspring. But transfer of larvae from males to females is easy: it happens during copulation. The author saw lots of females with beetles on their dorsal (top) surface, where they’d be transferred during mating, and witnessed at least one actual transfer during bee copulation.
The authors are careful to frame their hypothesis tentatively, which is of course that the beetle larvae have evolved a social behavior that helps them achieve the next stage of their life cycle: eating pollen in a bee’s nest. To that end, their behavior has evolved to make them aggregate and move as a unit. Genes that mandate this behavior would, of course, be advantageouos. This was (at least in 2000) the first known case of cooperative behavior in blister beetles, and the first known case of any cooperative behavior among individuals associated with mimicry. The authors also suggest that pheromone mimicry might be involved, since the bees appear to be interested in individual beetles before they form aggregations. Perhaps the beetle larvae (like some bee-fooling orchids) produce pheromones resembling those of female bees.
Note, too, that not all of the beetle larvae make it onto the bee (see comments below); many may die of dehydration. But note that they’re all brothers and sisters, and thus share many of their genes. You can thus see the communal behavior as the result of kin selection: you may die, but the genes for that behavior are present in your siblings who ride off on the male bee.
With that long introduction, showing once again the power of natural selection to create amazing forms of mimicry, I present the film that shows the whole ball of wax; the photography is remarkable:
And here’s a figure from the Nature paper showing a). an aggregation of beetle larvae on a twig (aggregations have a mean number of 549 larvae), b) A male bee with a bunch of beetle larvae on its ventral surface, and c) A female bee, presumably having mated with a beetle-laden male, showing the larvae on its dorsal surface.
Hafernik, J. and L. Saul-Gershenz. 2000. Beetle larvae cooperate to mimic bees. Nature 405:35.
26 thoughts on “A remarkable case of mimicry: beetles as a venereal disease of bees”
Jerry, your suggestion that pheromones may be involved is dead right. There was a subsequent paper in PNAS about 2005 which showed this, including videos showing male bees approaching extracts of tringulids. I teach this in my final year Chemical Cimmnication in Aimals course.I’ll post links later.
Matthew—can you give the reference for those who might be interested?
Or, better still, how ’bout a guest post on the subject?
I mention this amazing phenomenon in my book, too. But I wonder what happens as the larvae that don’t make it onto the bee remain stranded on the stem; the bee only takes a portion of them, and I don’t know how the likelihood of making it onto the bee is related to one’s position within the clump, say. After all, at some point it must get increasingly desperate trying, so to speak, to imitate the bee shape, and hence you have to ask how the last few siblings interact. For that matter, I wonder if the larvae can attempt to move to a more favorable place on the bee, or if that’s random.
Here’s the more recent reference:
Saul-Gershenz, L.S. & J.G. Millar. 2006. Phoretic nest parasites use sexual deception to obtain transport to their host’s nest. PNAS USA 103: 14039-14044.
Millar is actually in the Entomology dept at my university. Enjoy!
Thanks for the reference and the interesting questions.
Given the Mojave location of this case, I’d guess that the larvae left hanging onto the stem succumb to desiccation before their numbers get low enough for the mimicry to break down.
I’m using this in class on Wednesday.
Are there any other insects that show an at least somewhat similar behavior?
There are a lot of phoretic pollen- or nectar-feeders. For example, mites on a flower go up the proboscis of bees and butterflies, or the beaks of hummingbirds, when they visit the flower. They go back down when the bee, butterfly, or hummer visits the next flower. But those are pretty simple behaviors compared to this.
Here’s the Ateenborough original of the video, starting about 3:30.
Great link thanks, I didn’t think there was any Attenborough I hadn’t seen! Talk about adding insult to injury, eating the bee larvae after the pollen runs out seems to be pretty dreadful. If you’re a bee anyway.
Not to mention, counter-productive. (Reducing host ranks…)
Well, what with beetles bonking stubbies and actually BEEing a venereal disease, I wonder that the Christian Right doesn’t turn its attention away from human beings.
I notice also that beetles that bonk stubbies are Australian, which seems, shall we say, not altogether unsuitable, but the others are red-blooded American… though I suppose, what with gay marriage, the repeal of DADT, etc, Pat Robertson, Michelle Bachmann and her hubby, Albert Mohler and others would not be surprised.
It’s worth noting that in this situation, if a larva is more likely to end up on a female bee by being a member of one of these clumps than by its other alternatives (whatever those may be), high relatedness to other members of the clump is just icing on the cake. Cooperation is beneficial and should be selected for either way; it’s just -more- beneficial with high relatedness.
TL,DR: group selection!
Selection on individuals for joining groups is not what ‘group selection’ means.
To demonstrate GS, you’d have to show a benefit to groups (of behaviour that actually or potentially differs among groups) that outweighs a cost to individuals of taking part in the group behaviour. I don’t see that here.
Another example of ‘social mimicry’ could be the little-studied flatid ‘petal’ bugs form Madagascar (or not at all? I cannot find anything with a quick search):
The often sit together & look like flowers on a thin branch or stem – thus perhaps avoiding predation by looking like (cauliflorous) flowers? (Cauliflory, flowers arising directly on the stem, is a widespread trait in Madagascar).
….and their nymphs look like lichen; quite the mimicry-ing lifestyle they’ve got going here!
I don’t know if this proves anything; I know the bee in this video and he’ll screw ANYTHING.
If male bees are able to scrape off the beetles on their dorsal surfaces, why can’t the females? Why do the beetle larvae hang out on her back? And why can’t insects (most of them? all of them?) remove parasites from the ventral surface of their thoraxes – do legs just not bend that way?
Regarding the contact of the bee with the Meloe larval aggregation, the best place to see how this really happens is to look as the supplemental video attached the the 2006 PNAS paper. The ENTIRE mass attaches instantaneously, first on the ventral side of the male bee, then some shift to the dorsal side. The male is not able to scrape off the most of the larvae. He may get a few off (a range of 100 to more than 1000 larvae) when he hits the hot sand before flying off. A few (10-20) may be left on the blade of grass, which will not have enough collective pheromone dose to attract male bees so they well perish. If an aggregation gets picked up most of the larvae make it onto the male bee, they then get distributed possibly to other males (in mating ball tussles) and to females in mating attempts and matings.
Only one Meloe can survive in each Habropoda bee nest. Of the many larval aggregations in a given year only ~42% get picked up by a male bee so the siren call of most of the aggregations seems to fall a bit short, luckily for the bees.
Saul-Gershenz, L.S. & Millar. J.G. 2006. Phoretic nest parasites use sexual deception to obtain transport to their host’s nest. PNAS USA 103: 14039-14044.