I am extremely pleased that Current Biology has featured my focus-stacked yellow fever mosquito on this week’s cover!
This image challenged me. The small size of the animal required a motionless (=dead) subject for focus-stacking dozens of input photographs. But mosquito bodies are so delicate, so fragile, that they dry out and collapse in a matter of minutes. I burned through a few samples getting the lighting and levels right before finally nailing this one.
The cover accompanies new research from Joshua Raji et al in Matt DeGennaro’s lab showing how mosquitoes find us using our stinky acidic volatiles.
You may remember a recent viral video showing an undescribed predatory ant behavior. It turned out that myrmecologists Christian Peeters and Stéphane de Greef had observed these ants in the field, but they’d not assembled enough data to publish, leaving us all in the dark about how the ants coordinated the amazing millipede-hauling chains.
The astute observer will notice I’ve put flies at the top. This is no accident. Flies are important pollinators, but as Morgan Jackson recently pointed out, they are unjustifiably neglected in favor of the more popular bees.
There’s a story going around about how ants never have traffic jams. It’s a fine bit of science about how ants adjust their speed and don’t overtake each other, leading to smooth, fast speeds down the formicid freeway.
But I wouldn’t recommend humans adopt ant traffic management strategies. The physics of being small gives ants an enormous advantage.
Ant are tiny compared to us, and collisions at their size involve vanishingly small forces (remember F = [m][a]?), even at high speeds. Ants can cruise along with nothing to lose; the cost of veering into an errant stone or oncoming traffic is a slight bump, barely felt. They pick up and move along.
Cars? Not so much. You can imagine how much quicker rush hour traffic would move if drivers were immune to accidents, fearless and fast. People would drive like ants.
While we’re on spider debunkings, Piotr Naskrecki’s “puppy spider” story is making the media rounds this week, spawning the usual juvenile Nopes and Kill It With Fires! With every re-telling the spider gets bigger, of course.
they weigh up to 170 g – about as much as a young puppy.”
170 grams is big. By arthropod standards, it’s huge. But the spider is not, say, the Shelob people are imagining. For perspective, I’ve marked 170 grams on a standard puppy growth chart.
Puppy spider is not a 3 week old Labrador. It’s the weight, at birth, of a Chihuahua. Big, sure, but you’re not going to saddle this thing up and ride it to work.
The spider looks huge in the photographs for another reason, too. Piotr used wide-angle lenses that exaggerate the size of foreground relative to background objects. This wide-angle macro effect is a technique that Piotr does especially well. And it makes big spiders look larger than life.
Anyway, if you’d like one of Piotr’s puppy spiders for your living room wall, he’s just puta print on sale for prices so low he can’t be making any money:
Among the most dazzling products of insect evolution are leafcutter ants, which cultivate an edible fungus on a compost of fresh vegetation. The ants’ digestive chemistry is so simplified that they can only eat the fungus that grows in the underground gardens.
The leafcutter/fungus system is complex enough to seem highly improbable, and indeed, it appears to have evolved only once in the 130 million year history of ants. How could such a complex system appear?
The system did not spring forth fully-formed, of course. I was reminded of the gradual evolutionary transition on our recent BugShot course in Belize, when I happened across Trachymyrmex intermedius.
Contrary to appearances, T. intermedius is not a leafcutter ant.
At least, not technically. True leafcutters belong only to the genera Atta and Acromyrmex. Trachymyrmex is instead the sprawling, paraphyletic genus from which the leafcutters arose. These ants also farm fungus, but they typically use dead vegetation, caterpillar frass, and other bits of detritus. Like so:
Green vegetation is not the usual fare for Trachymyrmex, but T. intermedius and several others do take it on occasion. Seeing a few of these small ants trundling off with a harvest more fit for their larger cousins was just a reminder that animal behavior is naturally variable, and that variation is what allows the evolutionary process to explore new paths.
Those corners of the internet prone to viral outbreaks are abuzz today with an intriguing ant video:
Is it real? Yes.
The quality isn’t great, but the clip appears to show an Asian Leptogenys daisy-chaining their bodies in parallel lines to haul away a large millipede. I have spent the morning searching the technical literature for mention of this unusual behavior, and am coming up empty. Some Leptogenys species, including L. diminuta, L. nitida, and L. processionalis, are known to forage in groups and transport prey “cooperatively” (source, source). What is meant by “cooperative” is often vague. (For more, see this excellent recent review of cooperative transport by Helen McCreery). Yet I didn’t find any explicit description of workers linking up, mandible to abdomen, to pull together.
Is ponerine daisy-chaining an unknown behavior? Possibly. It is also possible my search skills aren’t up to the task. If you know of a description of it, please drop a note in the comments. I am not the only one interested, either:
I presume the swelling music helps motivate the ants to pull harder. But, I digress.
Steve Shattuck took a photograph recently in Borneo capturing a variation on this behavior, with workers forming a chain by biting the legs of a preceding ant.
Again, I don’t think the behavior has been formally described beyond this smattering of visual media.
Regardless of documentation, daisy chaining raises some definitely unanswered questions and will make a fine Ph.D. thesis for some lucky student. How do ants organize themselves in chains? What cues do they use? How do they know to let go? Is chaining employed only for particular sizes or species of prey? How does the behavior effect overall foraging efficiency? What are the evolutionary precursors to chaining? And, do these ants have any other tricks up their coxae?
***Update 8/30/2014 –
In the comments, Roberto Keller suggested that the eminent ponerophile Christian Peeters might know something. And indeed, Christian emails in with the following:
I observed this fascinating behaviour in Cambodia 4 years ago. Stéphane De Greef was with me and some of his photos are attached.
The behaviour was very stereotyped: mandibles grab preceding ant’s gaster (between first and second segment).
Seiki Yamane identified it as Leptogenys sp. 47, closely related to L. chalybaea described from Borneo by Emery (but stronger sculpture especially on gastral tergites).
The millipedes were 130mm long, identified as order Spirostreptida (Diplopoda). Ant is 16mm long.
Back then I reviewed the literature and found no other record of chain behaviour in Ponerinae. No record of millipede predation in Leptogenys. Specialized hunting on millipedes is restricted to Thaumatomyrmex, Probolomyrmex and Gnamptogenys, but these are solitary hunters on a very different kind of millipedes (polyxenids).
I started writing a ms on this behaviour (formation of chains in ants through a self-assembling behaviour) but sadly I have not been able to get further observations. It seems to happen at certain times of the year only.
By an amazing coincidence, two days ago I finished fieldwork in northern Thailand and came across the same Leptogenys species. There were cleaned out ring segments of big millipedes outside entrances. Unfortunately I did not observe any raids.
postscript: The virality of the video also illustrates both the good and the bad about the internet. The good, of course, is that this fascinating ant behavior found its way in front of scientists who otherwise might not have seen it. On the other hand, the viral nature of the video means that actual person who filmed it is drowned out among the hundreds of uncredited, unsourced copies. Securing the information about where and when the video was taken, and verifying the species, is going to be difficult. This is one reason why crediting sources online is important. Lose the credit, lose the data.
Five summers of monitoring the raiding behavior of 11–14 colonies of the slavemakers Formica subintegra and Formica pergandei revealed relatively frequent nest relocations: of 14 colonies that have been tracked for at least three of 5 years, all but one moved at least once by invading existing host nests. Movements tended to occur in the middle of the raiding season and were typically followed by continued raiding of nearby host colonies. Spatial patterns of movements suggest that their purpose is to gain access to more host colonies to raid.
2. Myrmica just can’t catch a break. A literature survey by Witek at al reports an array of about 40 parasites on these common holarctic ants, including butterfly larvae, socially parasitic ants, fly larvae, fungi, and others.
My sense is that Myrmica isn’t unusual in its parasite load; rather, Myrmica geography has lent itself to observation by natural-history obsessed northern Europeans. As myrmecology advances elsewhere, plenty of other ants will turn out to have lives just as miserable as Myrmica‘s.
3. The famous ant-killing Ophiocordyceps fungus, when injected into a non-host species, fails to induce the stereotyped death-bite behavior. From the abstract of a paper by de Bekker et al:
…brain manipulation is species-specific seemingly because the fungus produces a specific array of compounds as a reaction to the presence of the host brain it has evolved to manipulate.
The real news here is the development of a technique to infect the fungus across species and monitor the results. This method will be powerful going forward, especially since the test of specificity in this study is weaker than the title would suggest. The researchers only injected a single non-host Camponotus, and they’ll need more for a proper assay of host range. I presume such work is coming, as the Hughes lab is generally thorough and highly productive.
4. A parasite of fungus-growing ants provides convincing evidence for sympatric speciation. Older generations of biologists have been slow to accept that new species can arise while in physical proximity to their parent species, as mating between forms could erase any nascent differences. But Christian Rabeling et al have genetic data in Mycocepurus goeldii and its parasite M. castrator (ouch!) that make any other scenario highly unlikely. From the abstract:
Based on differing patterns of relationship in mitochondrial and individual nuclear genes, we conclude that host and parasite occupy a temporal window in which lineage sorting has taken place in the mitochondrial genes but not yet in the nuclear alleles. We infer that the host originated first and that the parasite originated subsequently from a subset of the host species’ populations, providing empirical support for the hypothesis that inquiline parasites can evolve reproductive isolation while living sympatrically with their hosts.
It’s the first video of live Tatuidris, among the rarest and least understood of all ants. Until recently, no one had even seen one alive. The video is from a new paper in Insect Science, where a team of Belgian myrmecologists report their observations on a recent collection of live specimens. Here’s the abstract:
Ants of the genus Tatuidris Brown and Kempf (Formicidae: Agroecomyrmecinae) generally occur at low abundances in forests of Central and South America. Their morphological peculiarities, such as mandibular brushes, are presumably linked with specialized predatory habits. Our aims were to (1) assess the Tatuidris abundance in an evergreen premontane forest of Ecuador; (2) detail morphological characteristics and feeding behavior of Tatuidris; and (3) define the position of Tatuidris in the food web. A total of 465 litter samples were collected. For the first time, liveTatuidris individuals were observed. Various potential food sources were offered to them. A nitrogen stable isotope ratio analysis (15N/14N) was conducted on Tatuidris tatusia, other ants, and common organisms from the leaf-litter mesofauna. We found a relatively high abundance of T. tatusia in the site. Live individuals did not feed on any of the food sources offered, as usually observed with diet specialist ants. The isotope analysis revealed that T. tatusia is one of the top predators of the leaf-litter food web.
So Tatuidris is a top micro-predator. But of what?
sources: Jacquemin J, Delsinne T, Maraun M, Leponce M. 2014. Trophic ecology of the armadillo ant, Tatuidris tatusia, assessed by stable isotopes and behavioral observations. Journal of Insect Science 14(108). Available online: http://www.insectscience.org/14.108.