Multiworm Egg (Apocalypse)
Pathetic. Absolutely Pathetic. If you run across one of these, just keep going. About the only thing they can do is spit weak acid, so your troops wouldn't even be harmed by a direct hit from this thing. It's not mobile, so it just sits there, and, frankly, if you can't capture one alive, which means that every alien besides this one is dead/unconcious, then you are a horrible X-Com Commander. It just sits there! How can you NOT capture it alive?
Official Entry (Captured Alive): "The gestation period for a Multiworm is approximately two days. During this time the egg will protect itself with a weapon that launches a fluid containing micro-organisms. These organisms consist of various types, some containing acids designed to erode metallic compounds and others containing unusual enzymes that rapidly break down organic matter. Fortunately the range of this weapon is limited. The Alien embryos are not sufficiently advanced to be susceptible to Psionic attacks."
Official Entry (Autopsy): "A large worm-like creature quickly develops inside the protective skin of the Alien egg. This worm appears to contain the embryos of a further four life forms. We cannot tell how the next stage in the life cycle develops from the autopsy results, but the tissues will be useful for our toxicology research."