Monday, December 9, 2013

Antlion


Remember back last summer when you could see soil, insects and other forms of warm life?  I saved this just to warm us up on a cold day.  This summer, Kim Christensen called me over to look at some mysterious holes in her raised bed gardens.  As we looked at the conical depressions, a small beetle slid down the side of one and bits of sand started flying upward.  Check out this video before reading on.

Out of a dark recess in my aged brain the term "antlion" emerged.  These creatures tend to live in warmer regions where there is sandy soil so our exposure is most likely from National Geographic* or the nature shows on TV.  Kim's imported garden soil was unusually sandy, a rarity in our rock covered Ozark hills.

Adult antlion - Click to enlarge -  Marshal Hedin- Wikimedia
Antlions are the larval stage of a very fragile looking winged insect which looks like a cross between a lace wing and a slow moving damselfly.   One key to differentiating them from the others are their clubbed antennae.  The adults are short lived, focused on reproduction and many species don't eat.  They may occasionally be found around lights at night.

Although some species have larvae that hide in wood or rocks to hunt by ambush, our common species use sand traps.  After they mate, the female lays her eggs in sandy soil.  Once the eggs hatch, the larvae become little eating machines.  By selecting fine grained sand to lay their eggs, the mother insures that her babies will have the perfect place to feed for up to three years of their larvalhood.

The consistency of the sand is critical.  The antlion will dig out a crater, hiding in the sand at the bottom.  The slope has to have a steep enough angle of repose so that anything on it automatically starts a little sand slide.  Once the prey slides to the bottom of the funnel, it is in deep trouble.  As it tries to climb out, the antlion tosses up the fine grains like a demented golfer in a sand trap.  The sand you see flying up as the victim tries to climb out both creates a small avalanche and loosens the footing underneath so that it continually slides down to the base.  Eventually the antlion grabs its prey and drags it under the sand.

The antlion larva is equipped with impressive hollow jaws with tubes that inject venom into the prey, digesting their body before sucking out the juicy predigested soup.  Although ants are frequent victims, they will take on any arthropod that wanders into their trap.  The larva may persist for 2-3 years before pupating, possibly a mechanism to compensate for its variability of food supply as it depends entirely on "who" drops in for dinner.

Our antlion larva
I recall a grade-school joke about the meanest animal in the world, the two-headed Wuwu.  And how did it poop?  It didn't, that was what made it so mean.  Badump bump!  This may be a factor in the antlion's ferocity.  It lacks an anus and stores all its solid waste from the larval stage until it is eventually passed as meconium near the end of its pupal stage.  This helps it retain fluid in its dry surroundings, even if it doesn't contribute to its temperament.

Sand coated pupa
 









The larva pupates by spinning a coating of silk with sand glued to it, a great camouflage.  The antlion holds the record for the greatest disparity of a small larva to a large adult among the insects undergoing complete metamorphosis.  This is primarily due to the long, thin frail exoskeleton of the adult.  Since it only needs to fly to find a mate, it doesn't require the heavier body of an insect that eats and survives for a longer time, the ultimate in reproductive efficiency. 

Citizen science doesn't require a lot of expensive equipment.  I would urge you to read the blog by Atmeeya Nayak, an observant student in India.  He provided the two pictures above as well as reporting on some very interesting personal experiments.


After the first beetle in Kim's garden quit struggling, a second larger beetle slid into the funnel shown above.  Twelve seconds into this video you can see the antlion jump out and try to subdue the larger beetle.

* Here is National Geographic's antlion video from Africa - loads slow but "a little" better quality than ours.
The antlion has a long history in literature, at first as mythical beasts until they were described by Albertus Magnus in his Opus Naturarum of 1255-1270.  See Antlion Pit.
As always, waynesword has a lot of information and pictures.

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