Archive | February, 2013

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.

Fluourescent Scorpions: Love and Danger in the Dark

8 Feb
Scorpions fighting at night in the desert, viewed with a blacklight.

Scorpions  at night in the desert, viewed with a blacklight.

One of the coolest night collecting tricks is to take a black light out to look for scorpions.  In the desert (and even in the woods where I live) these cryptic stinging critters emerge at night to hunt, and although they are well camouflaged a simple black light reveals them in glowing color.  There’s a lot of debate about why scorpions fluoresce under ultraviolet light but it may be a further mechanism to help them avoid light (which makes them vulnerable to predators and dehydration).

Scorpions that are not hungry reduce activity on brightly moonlit nights.  Being able to detect and head towards dark areas can also help an organism with relatively poor eyesight to quickly identify refuges such as rocks and bushes (Camp & Gaffin 1999).  Gaffin et al. found that, when blindfolded, scorpions could use their entire exoskeleton as a sensor to detect UV light (2011).  I am now enjoying picturing scorpions in tiny blindfolds.

Two scorpions fighting in the desert at night.

Two scorpions fighting (or courting?) in the desert at night.

I encountered this particular pair of scorpions in the desert in Arizona.  At first I thought they might be engaged in courtship behavior, but later I thought they might just be fighting (possibly both?).   Yes, I know the pictures look a bit violent with the wrestling and the stinging, but scorpion courtship is, well, probably only fun for scorpions.  I can’t find the excellent clip from Life in the Undergrowth, but there are some lovely videos of scorpion mating dances on Youtube.  For many species, stinging is involved.  Also elaborate dancing, and chewing on each other’s faces (“kissing”).  The courtship is completed when the male manuevers the female backwards onto a spiky spermatophore he has placed on a flat surface.

Scorpion chews on the face of a smaller scorpion with its chelicerae while pinning its telson in a claw.

Two scorpions: fighting or making out?


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.