Recently in Ant biology Category

Dear Ant Blog,

All the photographs I see show ants using their mandibles like tongs. Can they rotate them like we can rotate our arms?

Katrina

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Dear Katrina,

Despite the fact that ants use their mandibles for a multitude of different functions including prey capture, manipulation, and escape, there are no ants that have been proven to have fully rotational mandibles. Humans have a ball-and-socket joint that allows great range of motion, and although ants have a ball-and-socket joint for their antennae, their mandibles usually have a single plane of motion. Although this limits range of motion, it allows for much greater strength.

In case you are interested in reading more about mandibles, Chris Schmidt wrote a basic introduction to mandibular function as a part of the Tree of Life project. There are also several academic papers that detail the movements of mandibles (see Jurgen Paul), as well as some of the most extreme mechanical "trap-jaws" that have been convergently evolved by several ant species.

Hope this answers your question!

Best,

Max Winston & the AntAsk Team

Hello!

Thanks for taking the time to answer my question. I was recently traveling in Costa Rica and happened to take a camera shot of some interesting ant behavior. I have no idea what is going on here, but would sure like to find out. Have you ever seen this kind of behavior before? (see attached image)

Please let me know.

Mike

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Mike,

Great image! What you have documented here, quite beautifully, is a number of Azteca workers "spread-eagling" a Pachycondyla gyne (future queen). This is an interesting and well-known behavior of the genus Azteca (Dejean et al., 2009), which is well known for its mutualistic associations with plant species (Cordia, Cecropia). The mutualism between the plants and the ants relies on the plants providing food and shelter to the ants, and the ants fervently defending the plants from herbivores and other competitive plants. This behavior, known as "spread-eagling", is usually employed by the workers to protect the plants from insect herbivores or intruders, and is not restricted to the plant alone.

Because the Pachycondyla gyne has not started her colony yet and become a queen (you can tell because she has not dropped her wings yet), it is likely that the Azteca ants are showing this aggression to defend their territory before she can start a colony and get a foothold in their area. Although the pictures don't show it, I'm guessing the gyne did not escape alive.

Hope this answers your question, I've included the reference below.

Thanks,

Max Winston & the AskAntTeam

Dejean, A., Grangier, J., Leroy, C., & Orivel, J. (2009) Predation and aggressiveness in host plant protection: a generalization using ants from the genus Azteca. Naturwissenschaften. 96:57-63.

Hi guys,

First of all: this blog is really helpful, great work!

So now, while trying to write a report on ants --focusing on aspects of evolution-- I stumble upon many many questions. I'm hoping you can help me out!

1a. Micro-evolution
I was thinking about invasive species that are nowadays found in several continents, like for instance the Argentine fire ant.. Do all of their populations still belong to the same species? (no subspecies)
If so, how come? And would a male and female both from a different continent still recognize each other as potential mating partners or not. (If not, what's the term for that?)

What are specific factors that trigger origination of (sub)species of ants, or what causes the absence of it.

1b. Macro-evolution.. Can we speak of macro-evolution within the ant family, since there are so many different varieties. If not, could the relation between wasps and ants be an example of macro-evolution or is macro-evolution really about even bigger events?

2. Sexual selection
In the mating of ants, is there any 'conscious' selection going on from either gender. Are there species where an individual for mating is picked over another, based on qualities perceived?

Thank you!

Greetings :)
Zoe

Dear Zoe,

Thanks for your questions! You've gotten to some really awesome, fundamental evolutionary biology questions here, and you're asking me to make generalizations across a family of insects with more than 100 million years of evolution and more than 10,000 species, so I'm not sure I can do them justice in a blog post, but I'll try!

Your sub-question under heading 1a: "what are the factors that trigger origination of (sub)species of ants, or what causes the absence of it," is a question that can only be answered in a very generalizable way: speciation occurs when some factor causes populations of organisms to begin separate evolutionary trajectories. Often, as you suggest with respect to invasive species, this happens because of geographic isolation (allopatric speciation), but there are many theoretical and empirical studies that allude to the possibility of sympatric speciation, which is when speciation happens while populations of organisms are still within "cruising range" of each other. A previous blog post elaborates on speciation in the context of nest parasites.

Your first question about invasive species is great and very timely! There have been at least two studies in the past few years which demonstrated that Argentine ants (Linepithema humile) from different continents actually recognize each other as nestmates! So I can't imagine there would be any trouble with mating there.

The authors of both papers suggest that nestmate recognition is maintained across different continents because there is a steady stream of new arrivals, which prevents the populations from drifting apart. However, the question of when exactly a speciation event happens is very difficult to pin down. In a classic paper on the "Evolutionary species concept," the icthyologist EO Wiley states that "A species is a single lineage of ancestral descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate."

By this definition, you would really have to be able to predict the future: how can you know whether a newly isolated population will come into contact with propagules from its ancestral range? The idea that newly isolated populations are incipient species is tempting, but in practice, species can only be delimited if there are morphological and/or molecular differences in them, or, if you subscribe to the biological species concept, things could be argued to be different species if they generally choose not to mate with each other (for more information, you might want to look up pre-zygotic isolation and assortative mating...). In the case of the Argentine ant, I would expect a sudden drop in propagule pressure would result in the actual isolation of the disparate populations, but I would only expect this to happen if humanity drastically changed or ceased its practice of global trade and travel.

Sexual Selection
Speaking of pre-zygotic isolation and assortive mating, I think it makes sense to talk about sexual selection in the context of micro-evolution, because that's potentially a pretty important driver of speciation and trait evolution in sexually-reproducing organisms. Stearns and Hoekstra, an often-recommended text in evolutionary biology, defines sexual selection as: "The component of natural selection that is associated with success in mating." While at first somewhat disappointing, I think this definition is useful because it underscores the fact that sexual selection is a component of natural selection. Many ants form mating swarms, or leks, especially in desert and temperate zones. In these cases, there is a certain amount of "scramble competition," and differential levels of mating success have been demonstrated to correlate with individual traits. However, I am not aware of anything approaching the level of mate choice and the resultant secondary sexual ornamentations that has been demonstrated in some butterflies, odonates (dragonflies and damselflies), or other animals.

For a variety of reasons, the exaggerated secondary sexual traits that seem to emerge in classical examples of sexual selection (i.e., the tail of male peacocks) seem to be less likely to develop in eusocial insects (for a more in-depth perspective on this, check here, here, and here). In lekking species, there is likely to be a very important trade-off between the relative sizes of the flight muscles and the testis and ovaries. Some species of ants do not lek, and either engage in within-nest mating (intranidal mating: for example, some Cardiocondyla exhibit this incestuous behavior), and others engage in "mate-calling," like some moths. For these species, ability to give off (for the females) and recognize mating cues (for the males) is likely to be selected upon, but, to the best of my knowledge, selection on particular traits in these species has not been selected upon. By Stearns and Hoekstra's definition, sexual selection is likely to occur in any sexually-reproducing species, regardless of escalating selection for mate-choice.

Macro-evolution
I'll defer to Stearns and Hoekstra again for their definition of macro-evolution: "The pattern of evolution at and above the species level, including most of fossil history and much of systematics." By this definition, macro-evolutionary patterns are evident in any taxon above the species level, for example, the fact that genera such as Pheidole, Strumigenys, and Camponotus have many species, while Paraponera, Tatuidris, and Rostromyrmex have very few species is a macro-evolutionary pattern. More ant genera than usual seem to have arisen when the earths terrestrial vegetation came to be dominated by flowering plants, which is another macro-evolutionary pattern.

Traits can also exhibit macro-evolutionary patterns: ants are all eusocial - we don't know of any solitary ants. Asexual reproduction has cropped up several times in a variety of ant lineages, but does not seem to have persisted beyond a speciation event. The ability to cultivate fungus has only occurred once in the ants. The processes that gave rise to these patterns are somewhat outside of the realm of macro-evolution, but the justification for using the term "macro-", instead of referring to these patterns as just plain old "evolution," is that they cannot be predicted by an understanding of intra-specific evolution alone. This is analogous to the anti-reductionist argument that cell biology cannot be usefully predicted by chemistry alone--simply understanding osmosis and organic chemistry would not allow us to predict the utility of sexual reproduction, which in some situations can give rise to heterogamy, which in turn drives the emergence of a fertilization envelope, uniparental organelle inheritance, and, in one case, the tail of the peacock. In another case, irreducible patterns and processes random-walked their way to the population of weird little wasps that would become the ancestors of all ants.

As I said at the outset, one would need quite a bit more time and space to fully answer your questions, but I hope I've at least given you some food for thought.

best,
Jesse Czekanski-Moir & the AntAsk Team

Hello,

How come when it gets really hot ants are still able to run around on bitumen and pavers without burning their feet?

Regards
Anna W
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Dear Anna,

Although the thermotolerance of ant tarsi (feet) on hot bitumen or pavement has not been directly studied, there are a few biomechanic studies out there that can help us make some educated guesses.

Part of the reason ants may be able to run quickly over hot pavement is that their tarsi are composed of sclerotized chitin, which is a really tough polymer of many connected glucose molecules. The toughness of this biomaterial is often compared to the keratinized tissue seen in vertebrate hooves--such as horse hooves--many of which are also able to walk on hot bitumen and pavement. This is very different than human feet, which have many nerves and soft, burnable tissue on the bottom of our feet. Yet, even humans can walk on hot pavement if repeated friction and pressure forces the formation of calluses that insulate the sensitive tissue in your foot from the pavement.

While this explanation helps us understand how ants don't burn their tarsi (feet), it does not get around the larger of issue of how the ants on hot pavement deal with the increased body temperature (ants are small!). Well, as it turns out, there are some extremely interesting studies on ants that have adapted to hot, dry environments. One ant in particular--the Sahara Desert ant (Cataglyphis bicolor)--has adapted such a high thermotolerance that its proteins can operate at higher temperatures (4-5 degrees Celsius) and it can forage normally at body temperatures above 50C or 122F. Considering this ant makes a living by running on the hot sand to find and consume insects that have died of heat exhaustion, it makes sense that it can withstand this heat. While you wouldn't commonly find Cataglyphis running on pavement, there has been recent research showing that ants found in urban and suburban areas are more likely to come from hotter, drier habitats because of the prevalence of open areas in the urban and suburban landscape. Thus, it is logical that the ants you see running around on pavement might have also have some thermotolerance themselves!

Thanks for your question,

Max Winston & the AskAnt Team

Hi there.

I am a science teacher who traveled to Northern Kenya in July. While in Ndonyo Wasin (near Archer's Post), I observed many ant mounds under acacia trees. I was wondering if you could identify the type of ant that built this mound. I am also interested in learning more about their mutualism. I am writing a science curriculum about the environment that surrounds our sister school there, and would really love to learn more about the ants that inhabit the region. Any help would be greatly appreciated.

Thanks,
Maria
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Dear Maria,

The mounds in your pictures were made by termites, not ants. They are potentially interesting for their complicated caste system and symbiosis with certain fungi, similar to Attine leaf-cutting ants in the Americas.

However, I am guessing that the mutualism you are referring to is that between acacia trees and ants, not between termites and fungi. Such relationships do occur in Kenya between Acacia drepanolobium and three species of ant in the genus Crematogaster and one species in the genus Tetraponera. Unfortunately, the plant pictured here is not an Acacia drepanolobium, but that does not mean they are not present in the area. These plants typically grow on "black cotton" soils and are often the only overstory plant in the area.

Acacia drepanolobium trees are very easy to identify because they are full of hollow swollen thorns and are typically rife with ants, as in the picture below.

Photo by Eric Denemark

The basic idea behind the mutualism is that the plants grow the hollow thorns pictured as well as extra-floral nectaries and protein-rich food bodies. Ants nest in the thorns and feed on the nectar and food bodies and in exchange, they aggressively protect their host plants against herbivores. The ants are so effective that they can even protect their plants against elephants (Goheen and Palmer 2010)! The ants will not nest anywhere else and without ant residents, the acacias are quickly destroyed, making the mutualism obligate. Both organisms involved are completely dependent on each other. However, when researchers (Palmer et al. 2008) used fences to exclude large herbivores from a plot of acacias for a period of ten years, the plants actually stopped producing resources for the ants, because they no longer needed their protection. Without their host plants, these ants have nowhere to nest. This is yet more evidence that the extinction of single species can have wide-ranging and unexpected results.

In reality, the acacia-ant mutualism is much more complex than what I have outlined. For example, there is a high level of competition between ants of both the same and different species for nesting space because nearly every tree is occupied and founding new colonies or expanding current colonies necessarily means that confrontation must occur. The dominance hierarchy between species is closely related to average colony size (Palmer et al. 2000). No single ant of a species involved here is much better at fighting than any other ant so the largest colony usually wins. Ants also provide differing levels of protection to their hosts so plants experience different benefits depending on who is nesting in their thorns.

If you do find these plants and ants in the area, I would strongly encourage you to incorporate them into your curriculum. The four species of ant are easy to tell apart by the shape of their body and coloration of segments. See how the first two segments are red and the last segment is black in the ants in the picture? That means they are C. mimosae. C. nigriceps is black, black, red and C. sjostedti is all black. The single Tetraponera species, T. penzigi is also all black but has a long and thin body unlike the stocky Crematogaster species.

As you may have guessed, a lot of research has been done on the Kenyan acacia-ant relationship, predominantly by Todd Palmer's research group at the University of Florida and Maureen Stanton's group at the University of California Davis. I have listed a number of their publications below but you should definitely check out their websites as well. They have been featured in quite a few popular science articles that may be useful.

Thanks for your question and good luck,
Ben Rubin, James Trager & the AntAsk Team

Goheen JR, Palmer TM. 2010. Defensive plant-ants stabilize megaherbivore-driven landscape change in an African savanna. Current Biology 20, 1768-1772.
Palmer T. 1994. Wars of attrition: colony size determines competitive outcomes in a guild of African acacia ants. Animal Behaviour, 68, 995-1004.
Palmer TM, Brody AK. 2007. Mutualism as reciprocal exploitation: African plant-ants defend foliar but not reproductive structures. Ecology 88, 3004-3011
Palmer TM, Stanton ML, Young TP, Goheen JR, Pringle RM, Karban R. 2008. Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna. Science. 319, 192-195.
Palmer TM, Young TP, Stanton ML, Wenk E. 2000. Short-term dynamics of an acacia ant community in Laikipia, Kenya. Oecologia, 123, 425-435.
Stanton ML, Palmer TM. 2010. The high cost of mutualism: effects of four species of East African ant symbionts on their myrmecophyte host tree. Ecology 92, 1073-1082
Stanton ML, Palmer TM, Young TP. 2002. Competition-colonization trade-offs in a guild of African acacia-ants. Ecological Monographs, 72, 347-363.

Hi!

I am Natalie, I'm in 8th grade in chicago and i Am doing science fair, I am putting ibuprofen in ants food and drink. My question is: Will trace amounts of ibuprofen affect the behavioral patterns of red harvester ants? I have both on my ant farms set up, and 15 ants in each, I just would like some help along the way so i can do a great science fair!

Thanks and hope to hear from you soon.
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Dear Natalie,

We are glad to hear that you are participating in a science fair and that you are planning to include ants in your experiment. Regarding the experiment you are planning to conduct, here are a few things to consider:

- How will you measure the behavioral patterns of the ants to see if they are different? There are many ways to do this, but you will want to come up with some way to standardize your measurements. Will it be how much food they consume and how will you determine this? How often the ants are active versus not moving for specific periods of time that you are watching them? How often do the ants engage in different behaviors between the treatments (grooming themselves, grooming other ants, etc.)? There are lots of observations you could make, just be sure to decide ahead of time what you will do. One idea might be to just spend some time watching your ants before starting the experiments to get ideas.
- To insure that you are measuring the effect of the ibuprofen, you will need to have a "control", which in your case would be a group of ants that you are not feeding ibuprofen, but otherwise are treated and fed exactly the same. This will allow you to determine if the ibuprofen is what is causing the differences.
- You would ideally also like to have multiple pairs of ants that are and are not fed ibuprofen (but I realize this may not be possible for your project this year).

We hope this helps and have fun watching your harvester ants! Harvester ants from the genus Pogonomyrmex are beautiful animals (to see what they look like up close click here).

Enjoy,
Corrie Moreau & the AntAsk Team

Thanks for your question, Nathalie!

It is true that ants are proportionately much stronger than we are. I don't think any human could dangle from the ceiling with 100 times his or her body weight, like the weaver ant Oecophylla pictured here. There are many adaptations that are working together to allow ants to perform impressive feats like these: hairs on their feet that can stick to very smooth surfaces, large muscles in their heads to close their jaws, and light lean bodies. Most worker ants don't have functional reproductive systems, so their strength-to-weight ratios are higher than many other insects that are weighed down with the burden of perpetuating their genes.

However, comparing the proportional strength of even the strongest humans to an ant is unfair. Even lions, tigers, and bears (oh my!) can't lift more than 10 times their own body weight, as many insects can. Some of the physics behind this is explained here. The strength of ants is "super," but it is not super-natural. It all makes sense once you know a little more about physics.

Briefly, smaller organisms will always have bigger strength-to-weight ratios, because it's the surface area of the muscle cross section that determines strength, but the volume of the animal that (all else being equal) determines mass.

Less briefly: imagine three perfect cubes, each of a different length: 2cm, 5cm, and 10cm. The 2cm cube has a cross-sectional area of 2x2=4cm^2 and a volume of 2x2x2=8cm^3. The 5cm cube has a cross-sectional area of 5x5=25, and volume of 5x5x5=125, and the 10cm cube has cross-sectional area of 10x10=100 and 10x10x10=1000. If these cubes were animals (admittedly, very strange ones), the 2cm cube could have a strength-to-weight ratio that was proportional to 4/8, while the 5cm animal's strength to weight ratio would be 25/125 = 1/5, and the largest, 10cm cube-animal would have a strength-to-weight ratio of 10/1000 = 1/100. Of course, this is an oversimplification, but I hope this helps clarify why all of the proportionately strongest animals are very small.

Although this is an ant blog, I feel it is only fair to point out that ants are not the strongest insect, even proportionately to their body weight. The prize goes to a dung beetle, which can drag more than 1000 times its body weight. These beetles are larger than any ant, which makes their strength-to-weight ratio even more impressive.

The feat of strength in which ants have beetles beat is how rapidly some of them can close their jaws. Ants of the genus Odontomachus can close their jaws at speeds of up to 230 km/hr (143mph), generating a force that is 500 times their body mass. Not only are these forces very effective at subduing prey and smaller enemies, some of them can use their jaws to launch themselves into the air. This youtube video is completely worth checking out if you like wathching slow-motion ants flail through the air. For a more dignified synopsis, one of the original articles on Odontomachus jaws is here.

I hope this helps!
best,
Jesse Czekanski-Moir & the AntAsk Team

I'm thinking about doing a science fair project on ants. I was hoping to create a habitat for two colonies of ants and then connecting them by removing a plastic divider. Wanted to observe what the colonies would do and how it would change their behaviors finding food, etc. Also, I read that certain ants can float by linking together on top of water. Is this true? Will ants from two colonies link to survive?

Marion

Hi Marion,

We have several posts on ant farms here, and particularly this post might be of interest to you.

Almost all ant species will viciously defend their colony against ants from a different colony. This being said, once you remove the plastic divider, the two colonies would fight each other. If the two colonies are from the same species, workers usually fight one-on-one in often lethal fights and the larger colony would win. Check out this post by Alex Wild on territorial fights of pavement ants. If the ants you bring together are from different species, it is hard to predict which one would survive.

To answer your second question, fire ants can link together to float. This behavior actually helps this invasive species to survive during floods and to colonize new habitats. (To find out more about fire ants read this post.) Researchers have discovered the mechanisms behind these living floats and found that ants use the buoyancy of air bubbles to float. Linking their bodies together increases water repellent activity. Here is an article on the study by Mlot and colleagues, which was published in 2011 ("Fire-ants self assemble into waterproof floats to survive floods" PNSA 108:7669-7673).

I hope this answers your questions!

Steffi Kautz & the AntAsk Team

Dear AntBlog,

I have ants in my yard and garden. Should I leave them there or try to get rid of them? What good are ants?

Thanks,
David

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Dear David,

Ants are very important and we are glad you asked!

Although ants can spoil our picnics or become unwelcome visitors inside our homes, most ants are actually beneficial to have in our yards. Ants are important to many organisms through their environmental and ecological impacts. There are over 12,000 species of ants that scientists have given names and there are at least double and maybe triple out there waiting to be discovered. Not only do ants turn more soil than earthworms, aid in decomposition, and disperse the seeds of many plants, but they also kill pest species.

Soil Makers: Like earthworms, ants help create healthy soil. By digging tunnels, ants aerate and turn over the dirt, bring nutrients closer to the surface, and allow rainwater to circulate more fully through the soil.

Seed Sowers: Seed-harvesting ants increase the dispersal, survival, and germination rate of seeds. By carrying them to new habitats and storing them in nutrient-rich ant nests, the seeds can sprout in a safe environment, protected from seed predators as well as drought. This helps plants thrive in the wild.

Pest Police: Many ants prey on the eggs and larvae of bothersome household insects such as flies, fleas, silverfish, bed bugs, and even cockroaches. If left to colonize the pe- rimeter of your yard, ants can act as a barrier to termites and help keep pest populations down overall. The diversity of the total ant species in an ecosystem can be an indicator of overall environmental health. Having a diverse community of ants and other insects helps keep the entire ecosystem in balance, which is important for all the plants, fungi, and animals (including us) that share the environment.

So unless the ants are coming into your home, I would suggest that you leave them to preform their important roles in your yard. If you are having problems with ants in your home, then you can try following some of the advice we have given in the past:

http://www.antweb.org/antblog/ask-an-ant-expert/ants-in-your-house-or-yard/

So the next time you come across ants in your yard, take a minute to watch them and appreciate the important role they are playing in maintaining a healthy planet.

Enjoy the ants,
Corrie Moreau & the AntAsk Team

How far back does speculation go regarding the ancestry of ants? I have found that ants are thought to have come from wasps and I was wondering if speculation went further back to an ancestor for wasps etc. Is there a common ancestor that goes back to the sea?

Another question that I have is rather or not some wasps or wasp like creatures could have evolved from a line of ants, in other words the reverse of the theory that ants evolved from wasps?

Lastly, I am fascinated by ants that have an iridescent or blue hue and I found bees on-line that have an iridescent metallic green turquoise color. Is there an ant with a comparable appearance to this type of bee? Could these be related to the metallic bees? They look surprisingly alike.

Dear Pamela,

Ants and wasps are insects and are therefore members of the subphylum Hexapoda. Hexapods in turn belong to the phylum Arthropoda which includes crustaceans (crabs, lobsters, shrimp), myriapods (centipedes, millipedes), and chelicerates (spiders, scorpions, horseshoe crabs). All of these groups likely evolved from a shelled, aquatic ancestor. The evolution of land-dwelling behavior from aquatic ancestors appears to have occurred several times within this group. You should take a look at this study by Regier and colleagues and definitely check out Alex Wild's blog post discussing this paper.

Some of the strongest evidence that wasps are ancestral to ants and not the other way around is that the oldest known ant fossils are from about 100 million years ago, whereas the oldest known wasp fossils span back to around 150 million years ago. The changes in physical characteristics are also suggestive of a wasp to ant transition as an ancestral ant would mean that wasps had to reacquire wings and the ability to fly, rather than the far more likely loss of wings in ants. Lastly, phylogenetic analyses show that the ant clade (Formicidae) consistently nests within what we consider to be wasps, suggesting that ants are derived from a wasp-like ancestor (see this paper by Pilgrim and colleagues). All of this evidence taken together mean that it is far more likely that ants evolved from wasps than vice versa.

Ants and bees are related but every ant is more closely related to all other ants than they are to any bee. The same is true of bees in relation to ants. This means that the iridescent green color that is found in both ants and bees is a result of convergence to that character, not the close relationship of a particular pair of ant and bee species. In fact, there are many wasps that also have this type of coloration (see some of Alex Wild's beautiful photos here and here). These similarly colored species may use the same mechanisms for generating the necessary pigments, and these mechanisms may be present as a result of common ancestry but their expression is a result of convergent evolution.

Great questions!
Ben Rubin & the AntAsk Team