Posts Tagged ‘blue-winged wasp’

Predators of Predators in the Insect World

September 12, 2011

Here’s a better photo of a blue-winged wasp (Scolia dubia) than the one I posted a few weeks ago when I was showing how they destroy my grapes.  This photo is from google images.

A few weeks ago I gingerly picked grapes from my vine because yellow jackets and blue-winged wasps were also enjoying the fruit.  It occurred to me that I knew nothing about the latter insect, so I mind-melded with google for some interesting facts about them.  Blue-winged wasps are a member of the mutillid family which also includes velvet ants and cicada-killers–predatory insects that sting and paralyze their victims, carry them to underground lairs, and lay their eggs on them.  The eggs transform to the larval stage and feed upon the helpless insect.  That’s all the protein they’ll ever need.  When they become adults they only require sugar for energy, explaining why the creepy creatures haunted my grape vines.   Blue-winged wasps specialize in preying upon green june bugs.  June bugs are a garden pest, so blue-winged wasps are beneficial insects.

Photo from google images of a cow-killer ant, a kind of velvet ant (Dasymutilla sp.).  They’re not actually ants but instead are wingless wasps.  They’re pretty common in my yard.

Cicada-killers (Sphecius sp.), as the name would suggest, specialize in preying upon cicadas.  But velvet ants, also known as cow-killers because their sting is painful enough to kill a cow (an exaggeration, of course) parasitize cicada-killers and bumble bees.  They show no mercy to their close relatives, nor to their distant bee cousins.  They are predators of predators.  I often see these wingless solitary wasps scurrying about bare soil areas in my yard, especially where the grass has been killed by the cars I park on the lawn.  (I purposely park on the lawn.  Less grass to cut.)  Bare soil was a common habitat during the Ice Ages.  Frequent drought and megafauna overgrazing, trampling, and digging created many spots devoid of vegetation.  Moreover, many species of wild grasses grow in clumps rather than forming carpetlike lawns.  The mutillids like bare soil because it’s easy for them to dig their chambers without having to go through a grass barrier.  Because favorable habitat was abundant during the Ice Ages, mutillids must have been as well.

I didn’t think I’d find a Pleistocene angle for this group of organisms.  Studies of Pleistocene insects are rare although there are some.  Insects are less likely to be preserved than fossil vertebrate bone or shelled molluscs.  I was surprised to find that there has been a study of Pleistocene mutillids.  Scientists determined that changing Pleistocene climate phases increased species diversification of nocturnal velvet ants in southwestern North America where at least 300 species live.  Speciation occurs more rapidly in the insect world because several generations of the short-lived creatures can live within the timespan of just a year, greatly speeding up the possiblity of evolution.  Scientists used an analysis of velvet ant DNA to make this determination.

Reference:

Pitts, VP;  JS Wilson, and CD von Dohlen

“Evolution of the nocturnal Nearctic Sphaeropthaliminae velvet ants (Hymenoptera: Mutillidae) driven by Neogen Orogeny and Pleistocene glaciations”

Molecular Phylogenetic Evolution 56 (1) July 2010