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Gypsy Moth Egg Masses
How to Count Egg Masses

Gypsy Moth ProgramBy counting gypsy moth egg masses we can estimate the size of the following year's outbreak.

In 2008 we have greatly reduced egg mass numbers in the county. With many old egg masses left over from the 2007 infestation, it is important that only new egg masses are counted as the old ones are no longer viable.

To estimate how many egg masses you have in an acre, count every one that you see in a circle with a 20ft radius. Then multiply the resulting number by 40.

Old and new egg massesTelling Apart Old & New Egg Masses

Color: New egg masses are light brown in color and have a sheen whereas old ones appear much paler, often almost white.

Feel & Texture: Press gently against a new egg mass and it will feel solid. An old egg mass will feel very spongy and have plenty of 'give'.

Holes: Old egg masses have many holes in them where the caterpillars emerged. New ones generally have a smooth surface, although some may have holes where they have been parasitized.

A new egg mass clump2008 Egg Mass Characteristics

Size: The gypsy moth population in Central PA is stressed (probably due to a virus) and consequently females produced small egg masses. Their sizes usually vary from dime to nickel size.

Position: Weakened females often weren't able to climb a tree, so many of the smaller egg masses are laid very close to the ground.

Clumping: Another phenomenon that's apparent in 2008 is 'clumping', where numerous egg masses were laid close together and have blended to form a single clump.

Numbers: Previously infested areas have experienced a population collapse. If you see that almost every limb on a tree is covered with egg masses, they are probably old ones. Apply the rules above to make sure that you're only counting new ones.