Can someone explain 'test eggs' please? :)

[skagirl88]

I have one A. fulica, 3 years old, and I've always kept it on its own. I know that snails are capable of storing sperm from earlier matings but I have had this snail since it was a baby about as big as a 20p piece, they don't mate this young do they?

The other day I found a single egg, not buried, just left on top of the soil. I've tried to look online to find out why it would lay one egg and keep finding the phrase test egg. Is this a test egg?

Why do they lay test eggs? are they usually infertile? if my snail has produced eggs without mating will they be infertile or are single snails capable of producing babies (I know that some kinds of animals can do this) If it is an indication the snail will lay a normal sized clutch, is there a time frame for how long after the test egg they lay the rest of the eggs?

Sorry for all the questions, I would appreciate any information people can give

[pinkunicorn]

I'm also curious of any info anyone has on this, especially research material. I've not seen this happen myself but lots of folks have. I wonder about the evolutionary benefits of a test egg; as comments suggest it's usually a tiny amount of eggs or just one laid and thus not a large amount of resources wasted. Since it is done there has to be some reason for it. Are they perhaps comparable to human periods in some way (where the egg itself is not a huge wasted resource, but the effort is put into the baby after fertilisation)? Why do they do it?