Egg Cases

Winter is only days away (December 22), animals of all sorts are participating in the next step of the life cycle; the reproduction stage. A majority of animals have their young emerge during the warmer seasons, spring/summer, where food is more plentiful. Insects, arachnids, and gastropods lay eggs in the fall/winter months to allow the next generation a better opportunity to survive.

Egg cases come in all different shapes and sizes as they relate to their species. Some animals such as slugs lay eggs under moist logs; praying mantises lay their egg case on trees and arachnids leave their egg sac on or near their web. Their purpose in life is to produce the next generation, after they succeed, they will die. Here are three examples of egg cases and their young that will hatch from them in the spring.

Praying Mantis
The egg case of the Praying Mantis is composed of a frothy substance that eventually hardens. Inside the egg case, which is called an ootheca, the number of eggs can range from 10-400 individuals. They emerge from the mass once the temperature warm up, usually in April. The praying mantis then goes through 3 stages of metamorphosis, egg, nymph, and adult.

Black and Yellow Garden Spider
After copulation the female produces an egg sac that is only 25 mm in diameter but still encompasses 400-1,400 eggs. The sac is protected by the female in the center of the web until she dies from the first frost. The eggs hatch within the autumn months but they stay within the sac until spring time; this is called overwintering. During the winter months, the spiderlings are protected within the layers and layers of silk that was produced by the female.

The small opaque eggs found under rocks and logs come from the slimy slug. The mating ritual of this organism is very unique because they are hermaphroditic (has both male and female reproductive organs). One slug will follow and devour the mucous path from the other slug. As they meet up, they make a circle around each other to start the reproduction process. After the completion of copulation, it takes 8-10 days for eggs to develop. Depending on the species, slugs lay between 500-1,000 eggs in small batches throughout the forest floor. They will hatch out of their eggs once the warm season arrives.


Chinese Praying Mantis (Tenodera aridifolia sinensis)


Black and Yellow Garden Spider (Argiope aurantia)


Slug (Family Limacidae)