Cannibalistic Monarchs???

[Martha V. Lutz & Charles T. Lutz]

Hello!


Can anyone confirm (or refute) for me that Monarch larvae will eat
conspecific eggs?  A few years ago while raising Monarchs I lost an egg.  I
thought I had miscounted eggs, or perhaps misplaced one, or maybe the kids
took it out and didn't put it back.  I thought about that disappearing egg
today--when it happened again.

Today I found three newly-laid eggs and a small larva (probably about 36
hours old) all on the same milkweed plant in Linn Co., IA.  I put all three
eggs and the larva into one large (5-gallon) cage together.  A few hours
later I only had two eggs and a larva in the cage.

The missing egg had been on the upper surface of a leaf; the small larva
was on the under surface of the same leaf about 5 cm away.  After examining
the leaf (post-loss) with a magnifying glass, I concluded that something
ate the egg without biting into the leaf surface.

This raises the intriguing possibility that Monarch larvae are
cannibalistic, and that they will eat conspecific eggs NOT as a careless
side effect of munching on a leaf that happens to have an egg attached, but
as a deliberate act.

Usually I raise Monarchs in age group cohorts, so there have not been many
opportunities for cannibalism in my cages.  It has never (to my knowledge)
happened with the Saturniids that I raise.

I can think of several possible evolutionary selection pressures that would
promote cannibalistic behavior in Monarch larvae, but that does not mean
that any of these hypotheses are correct.  Does anyone else have
information or observations about this phenomenon?

Thanks!


In Stride,
Martha Rosett Lutz

P.S.  We were actually in Lisbon IA for a 5K road race.  I got beaten by my
kids again (which I enjoy, though!) and finished 2nd in the middle-aged
ladies' division.  The Monarchs were a bonus:  found 'em in a weedy garden
next to the race registration area.