Sunday, May 7, 2017

Praying for an Epidemic

I sat out in the backyard for an hour a few days ago and stood up covered with tiny gypsy moth caterpillars.  I would guess there were over fifty--mostly on my pants and around my shirt collar.  Thankfully, I didn't find any in my hair.  After the bumper crop of eggs laid last year I expected this would be a bad year, but thought I'd be okay under my little shelter.  I'm guessing they parachuted down at an angle on caterpillar silk. 

Gypsy moth caterpillars start out tiny, spindly and blackish, but quickly grow to become colorful and (gritted teeth) quite handsome with red and blue spots.  In a bad year, their frass (poop) falling on dry leaves can sound like rain.  Besides soiling the wash hanging on the line, the frass causes an allergic reaction in some people. 

Of course, the caterpillars are merely an annoyance to us; to trees it can be deadly.  I've seen trees (even whole forests) denuded by gypsy moths come back later in the season with a full suit of new leaves--but growing that new foliage can deplete a tree's resources so that other stresses tip it over the edge. 

Recent rain is very welcome: wet encourages the spread of the caterpillar's nemesis, the parasitic fungus Entomophaga maimaiga.  This fungus--which affects only the gypsy moth caterpillar--spreads through the air from an infected, dead caterpillar to others.  It cannot wipe them out, but keeps the population in check most years.

(The story of this imported, species-specific fungus is interesting in its own right: a century-old attempt at biological control that failed--then later succeeded when the fungus was accidentally reintroduced thirty years ago.) 

Technically, I'm praying not for an epidemic (which is "upon the people"), but an epizootic.

Almost-full-grown caterpillar in June; male with female moths laying eggs in July last year.

In other news,

the rains these last few months have been ending the drought.  Our local reservoir, Silver Lake, went from one hundred inches below normal at the beginning of the year, to just a foot below normal recently.  This weekend's rain may be a double blessing.

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