Several years ago I was doing research in Florida and I discovered
that, if you look carefully at the eggs on the milkweed plants, some
had been eaten. Then
one day I discovered that they had actually been eaten by monarch
do they get out of their own eggshells? They have to eat their way
out. And, for a few minutes after they have managed to eat their
way out of their own eggshell, if they're walking around and they
happen to find another monarch egg, they will start eating it. So
basically, they young larvae are cannibalistic. They will eat other
individuals of their own species.
we discovered in this field that there were two species of monarch-like
butterflies--the other is called the queen--and it also occurs along
the Gulf Coast states. Both monarchs and queens lay their eggs on
the same milkweed. We found that not only were they eating their
own eggs but they also eat each other's eggs. We found by setting
up an experiment that the queen monarchs ate more monarch larvae
than the monarch eggs than they ate of their own. So one of the
hypotheses that we had many years ago was that the origin of the
migration was to get away from the queen because of this egg cannibalism.
you watch monarch females that are coming in to lay eggs on milkweeds--anywhere
in the country--they usually only lay one egg at a time. There's
good reason for that, and I think you know what it is now.
you find a whole bunch of monarch eggs together that have been laid
on a milkweed it means that something is wrong with the female.
She's either sick or very, very old and can't hold back. Or, she
has been flying along for a long time and several eggs have matured
and she lays all of them at once. We really don't know all of the
details, so there is a place that one could do a very interesting
normally, after they lay one egg, there's a refractory period of
several seconds or maybe one minute. They fly up and they may come
back down again and they may lay an egg on the same plant but usually
not in the same place. If that refractory period is for a minute
or two they'll fly around and by then they'll have found another
milkweed plant. So they really do spread their eggs all over the
place, and one of the reasons they do that is they are cannibalistic.
This is all speculation, but one of the reasons monarchs may just
keep going is so they spread those eggs out over all of those plants.
So, if you're going to fly, keep flying northeastwards and you'll
cross over milkweeds all the way up to the Great Lakes--and that
new generation does that.
when a female monarch is coming back from Mexico and is looking
for milkweed plants, she has to be really, really careful not to
lay more than one egg on the same leaf--or even better on the same
milkweed plant--because if she does lay more than one egg and they're
close together the first that hatches out is very likely to eat