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If you give an ant a cookie…

22 Feb
Harvester ants fighting to carry off a cookie crumb.

Pogonomyrmex and Aphaenogaster ants wrestle for a cookie crumb.

At the Southwest Ant Course last summer, I got the chance to participate in some cool biodiversity assays of the local ants, comparing assemblages before and after a flash flood.  Among other things, we pit-trapped, counted nest entrances, and scoured the ground for wandering ants.  To encourage ant activity, quadrants were sprinkled with cookie crumbs.  We were using crumbled up pecan sandies because, and I quote, “those are ants’ favorite cookies.”

I can’t speak for any given ant (I, personally, prefer Thin Mints), but the desert ants of Arizona certainly did seem to like pecan sandies.  I’m also going to go out on a limb and speculate that these cookies are useful as assay tools for their combination of sugars, proteins, and lipids in order to attract ants with a broad variety of diets.

Ants fighting for cookie

Two different species of desert ants continue to wrestle for a cookie crumb.

Pogonomyrmex (harvester ants) and Aphaenogaster (BugGuide calls these the “spine-waisted ants”) were by far the dominant species in the area.  The ants pictured above wrestling over a cookie crumb were in between two nests, and each was determined to get the prize back to her own colony.  I watched the ants play tug-of-war for several minutes, sometimes even picking up the cookie crumb with the other ant attached (as in the photo above).  Finally, the Aphaenogaster was joined by two of her nestmates, and the out-numbered pogo almost immediately surrendered the prize and fled the scene.  A rousing victory for Aphaenogaster-kind, who I assume went home to celebrate with cookies and tea.

Numbers win wars.

Aphaenogaster ants team up to wrestle a cookie crumb away from a lone Pogonomyrmex ant.

FYI, I believe these were Aphaenogaster albisetosa and Pogonomyrmex maricopa but don’t quote me on that.

Biting and Stinging: The Ants

1 Feb
Red imported fire ant (Solenopsis invicta) close up.

A fire ant biting and preparing to sting.

Do ants sting or bite?  I get this question a lot, and the answer I give is: “both–sometimes–it depends.”  This is the kind of helpful answer that makes me near and dear to friends and family.  So let’s break this topic down.

Most ants bite–or in other words they have mandibles (jaws) with which they can grab or pinch objects.  However, many ants are too small to effectively bite humans.  Ants are in the order Hymenoptera, and like their bee and wasp relatives, most female ants have venom and many have a stinger modified from the ovipositor (egg-laying structure).  Thus, many ants both bite and sting.

Fire ant (Solenopsis invicta) sting up close.

Close up of a fire ant stinger.

For example, fire ants first bite, grabbing hold with their mandibles, and then sting repeatedly, injecting venom into their victim.  This is why a quick swat at a biting fire ant can often remove them before they sting.  Some very small ants, such as the fire ants’ tiny relatives the thief ants, have stingers too delicate to pierce human skin.  On the other hand, some ants like leaf-cutter ants are so well adapted for biting that they no longer have a stinger.

Leafcutter ant heads used to pinch a cut closed.

Leafcutter ant heads used to pinch a cut closed (Photo courtesy P. Lenhart).

However, not all ants with venom have stingers.  Ants make use of a number of structures to spray, wipe, rub or otherwise dispense harmful chemicals.  One prominent example is the formicine ants (Formicinae), a large sub-family of ants which make use of an acidopore to disperse venom.  The acidopore is basically a round nozzle at the tip of the abdomen which ants use to spray formic acid.  Many formicines have a ring of hairs surrounding the acidopore which  can be used to help direct the spray.

Myrmecocystus (Honeypot Ant) close up of acidopore (formicidae: formicinae) under high magnification.

The acidopore of Myrmecocystus, a formicine ant.

Spraying formic acid is a very effective technique when used against many other arthropods and small animals, but generally goes completely unnoticed by humans.  However, for the myrmecologist collecting ants with an aspirator, formicines are extremely noticeable, and suction collection is often followed by a cough.  Inhaling formic acid is not fun.

A curated specimen of Myrmecocystus

Full shot of the honeypot ant (Myrmecocystus) pictured above.  The curled under abdomen is a typical posture for spraying formic acid.

Spiders raiding ant nest

3 Sep
Spider predating on Pogonomyrmex nest at night.

Spiders slip inside a sleeping harvester ant nest to prey on the worker ants.

Last week I had the pleasure of attending the new Ants of the Southwest course at the Southwest Research Station in Arizona, and I thought I’d jump right and share with you my favorite entomological encounter.  While black lighting in the desert we happened across a harvester ant nest that was being raided by dozens of small hungry spiders.  The spiders would slip inside the nest entrance individually and emerge some time later, dragging worker ant prey.   It was pretty impressive to watch, particularly as there was no evidence that the spiders’ raiding was provoking any kind of response from the colony.  Harvester ants (or “pogos,” from Pogonomyrmex) are a group of ants with a fairly vicious sting, and the workers dwarfed their tiny spider predators.

I’ve included more pictures as well as a video below, with bonus excited chattering commentary.

Spider entering Pogonomymex nest and killing workers.

A spider drags its harvester ant prey from the sleeping nest.

I don’t have an ID for the spider as of yet.  Several group of spiders are known to mimic ants, either to help them obtain prey or to help them avoid predators.  If these spiders don’t look like ants to you, it’s possible they may smell enough like ants to fool the colony.  Cosmophasis jumping spiders use this scent-disguise tactic to enter weaver ant nests and prey on workers and larvae.  Meanwhile certain spiders in the genus Masoncus take this a step further and live only inside harvester ant nests, where they prey on another nest symbiote, collembolans.

Spider feeding on its harvester ant prey.

A spider hangs from a grass blade, feeding on a harvester ant many times bigger than itself.

Update:

Thanks for the feedback here and over at Bugguide.  These spiders appear likely to be members of the family Theridiidae and the genus Euryopis.  Many members of this genus appear to be specialist predators of ants.  I poked around in the literature and there are a couple of papers about the species E. coki, a specialist predator of another species of harvester ants, Pogonomyrmex owyheei.  (I believe the harvester ants pictured above were P. maricopa.)  There were a number of similarities to the behavior I observed.  E. coki was observed to lurk outside nest entrances and ambush ant workers, first tacking down a leg with silk and then biting the ant.  When bushes or grasses were nearby the spiders employed a dangling feeding behavior (Porter and Eastman 1982).  Dale Ward has a great shot of a male Euryopis mating with a female spider near the nest entrance of P. rugosus.  Tetramorium’s Ants of Arizona page also has some great shots and info.  I haven’t been able to find any literature on thespiders actually entering the ant nests, though.

We Have to go Deeper

25 Jul
Yellow fuzzy braconid wasp cocoons (egg-like) clustered on a stick.

A mass of yellow cocoons attached to the end of a twig.

Hi!  It’s been a few weeks, hasn’t it?  I have all these pictures and draft posts but no time to finish any of them because I am trying to get my analyses done for the ecology conference this August.  I am tragically productive.

Here are some cocoons I found up at the Oklahoma biostation back in spring.  Cocoons are awesome because they are basically insects you can rear without actually doing any work.  I stuck these guys in a jar for a week or two to see what would emerge.  What I got was tons of tiny black and brown wasps.  I took some pictures under a scope and threw them up on BugGuide where I they were quickly ID’ed by the excellent Bob Carlson.  BugGuide is awesome, because it is basically network of experts you can access without actually doing any work.

Close up of a female parasitoid wasp.

A female braconid wasp (Cotesia), emerged from the cocoons.

The black wasps turned out to be members of the genus Cotesia, in the family Braconidae.  These are parasitoid wasps which lay their eggs on (or in) caterpillar hosts.  The larvae develop inside the caterpillars Alien-style, slowly eating them alive, before eventually emerging to pupate and seek out new hosts.

A female hyperparasitoid ichneumonid wasp.

A female ichneumonid wasp (Mesochorus) emerged from the cocoons.

The brown wasps turned out to be a species of Mesochorus which are hyperparasitoids of the original black wasps.  These are parasitoids of parasitoids which lay their eggs in the egg or early instar larvae of the Cotesia parasitoid wasp as it develops in the caterpillar host.  (Read that sentence back to yourself until it makes sense.)  If this arrangement seems unnecessarily complex to you, just realize that hyper-hyperparasitoids also exist.  Every “hyper” kicks it down another level.  It’s basically the plot of “Inception” but with innards-devouring bugs instead of dreams.  (“Insection“?)

Green Rooms and Gall Wasps

16 Mar
Galls formed by cynipid gall wasps in a leaf.

Eucalyptus leaf galls formed by gall wasps.

This is a green bug for St. Patrick’s day.  (I’m reaching; I know.  Happy Birthday, Eric!)

I’ve talked a bit about gall-forming insects in the past, but I think it bears repeating how extremely cool this adaptation is.  Galls are created by parasites (fungi, bacteria, mites, wasps, aphids, flies, midges, psyllids, etc.)  that use chemicals to co-opt the physiology of their host and cause the plant to grow abnormal structures that make a comfy little home for the parasite in question.  Opening up these particular leaf galls revealed tiny wasp pupae, developing in the safety and luxury of their own private green room.  Chemical warfare at it’s most refined.

Cynipid gall wasp pupae inside a leaf gall (Cynipidae).

Tiny gall wasp pupae inside a leaf gall.

P.S.  Does anyone know if any wasps outside Cynipidae form galls?  That’s the only family I’m familiar with.

Fire ants vs. Rasberry crazy ants

2 Mar

Here’s an interesting video for you of some interactions between fire ants (the invasive ant species closest to my heart) and a newly invasive ant species beginning to spread across Texas.  Rasberry crazy ants (Nylanderia sp. nr. pubens) were first noticed in the Houston area around 2002.  (For people who don’t keep up with the world of ant taxonomy, most of the genus Paratrechina was moved into Nylanderia in 2010.)

Crazy ants take their name from the way in which they run about very quickly while turning frequently.  The common name is applied to a number of ant genera.  As you can see in the video these ants are fast.  I’ve personally witnessed another invasive “crazy ant” (Paratrechina longicornis) fall into my fire ant colonies and become trapped many times.  Although they can’t climb out again and they are vastly overnumbered they’ll hang out in little groups by the water tube for days, apparently too fast for the fire ants to catch.  Trying to squish them is like playing whack-a-mole.  They also got into the sterile buffer and the coffee.

Thanks to Danny McDonald for providing the Rasberry crazy ants and helping to referee their valiant battle.  Danny is one of the few researchers working in this system right now.

Baby, Baby, Baby (Ants queens and brood)

20 Jan

Since I’m on the topic of mating flights and founding colonies, here’s a video of some fire ant foundress queens tending their eggs, brood, and young workers.

…I sort of really, really want to add Justin Bieber’s “Baby” as the sound track to this video.  Would that be too much?

Swarms of Fire Ants

16 Jan
Solenopsis invicta and alates swarming for nuptial flight.

Fire ant workers swarm defensively prior to a mating flight.

Sexual fire ants typically fly on clear, windless afternoons following a rain.  Workers open large holes in the nest, and then spread out, swarming the surrounding area to eliminate any potential threats.  Male and female alates are urged out of the nest, where they typically climb surrounding plant material before taking to the air to seek a mate.  Below are a few clips of a colony I found swarming on a sidewalk near my house.

See related:

Alates Leaving Home

A Heap of Queens

The Sad Plight of Male Ants

Queen Ants: Founding a new colony

Alates leaving home

13 Jan
Pyramid ant workers guard an alate at the nest entrance.

Pyramid ant workers (Dorymyrmex) guard alates as they emerge from the nest (Argentina).

Many ants mate in nuptial flights, taking to the air to seek out a mate among swarms of their kind.  After walking through one such swarm on his way to class, my labmate Collin told me, “Help, I’m covered in queens.  Would you like any?”

These flights are often synchronized by seasonal and environmental cues to insure everybody makes it to the party at the right time.   Winged future queens and their short-lived male counterparts then emerge from underground tunnels and prepare to take to the skies.  As the alates gather, the workers mill around protectively, making sure everyone stays safe and nobody leaves until the time is just right.  Sometimes workers drag out reluctant alates–the free ride is apparently over and it’s time to kick the kids out of the house.

Most of these alates (and all of the males) won’t make it.  But some of the female alates will eventually drop their wings and become the mothers of a new generation of workers and alates.

See related:

A Heap of Queens

The Sad Plight of Male Ants

Queen Ants: Founding a new colony

 

 

Big-headed ant majors need to be 20% cooler

6 Jan
Tiny major and minor pheidole ants and brood.

Major and minor worker big-headed ants (Pheidole).

Pheidole, the big-headed ants, are a charmingly hilarious genus of ants.  The typical workers (minors) are small and delicate.  The soldier caste (majors) are just a bit bigger with hugely over-sized heads.  They always make me smile.  The ants above are from a polygyne colony I picked up in a dead branch.  They live in the lab with my fire ants (okay, not with my fire ants) and come on visits when I do outreach.

Pheidole majors defend minors from a pen.

Pheidole workers examine a pen.

These guys are in the news recently because of research that has been done on a rare third caste that occurs in some Pheidole species: the supermajor.  These guys are majors, squared.  Their hilariousness is also squared.  Intriguingly, recent research indicates that this caste may have independently arisen by the same mechanism each time–a mechanism which scientists can mimic in other Pheidole species to create false supermajors.  Alex Wild has an excellent break down of the topic over at Myrmecos.

Pheidole ants and brood in rotting wood.

Pheidole majors (upper right) defend an opened nest while minors carry brood to safety.

And of course, check out his follow up post,  These People are Killing Journalism, to see the media handling the topic with their usual intelligence and dignity.

On the other hand, I do have a new career aspiration.

Mutant Ant Shirt by WearScience
(Shirt via WearScience)