Most Spanish slugs have an annual life cycle. They hatch in spring; the adults are present in the summer and subsequently die in late autumn. The main egg-laying period is between August to September. Spanish slugs can lay 70 eggs per clutch and a total of 400 eggs in their lifetime.
Slugs typically spend the winter as eggs in protected sites, like under plant debris, mulch, boards or in the soil. Eggs hatch the following spring.
In spring they can cause the first signs of damage, but maximum seasonal feeding and mobility occurs in summer. At the end of the summer, they reach sexual maturity and reproduce.
Some Spanish slugs overwinter in thermally buffered hibernation sites where temperatures rarely dip below 0°C. These are usually underground and provide protection from the worst winter frosts. These Spanish slugs may live two years.
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The hole you see on the right side of the snail’s mantle is for breathing and is called pneumostome.