Insects go through the larva stage before metamorphosing into an adult. The type of insect will determine where the eggs can be found. For example, dragonfly and mosquito larvae are found near water while caterpillars are found near plants and moist areas. The mother lays the eggs in an area she feels the eggs will hatch, be safe, and find plenty of food. If larvae appear on a window screen then there must be food nearby for them to eat once they hatches. They can be identified by analyzing their size, color and residue left behind.
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Analyze the coloring of the larvae. Insect larvae that would be on a window screen are either white or brown with black or white heads. Moth and butterfly larvae are caterpillars. Caterpillars vary in color in accordance to their surroundings and as they grow larger. Maggots are completely white.
Examine the size of the larvae. Caterpillars will have a hardened head with a soft body. They begin at about 1/16 inches long, growing longer and thicker the more they eat. Maggots are less than 1/8 inch long and soft bodied.
Look for small white residue on the window screen. Caterpillars leave behind sticky or silky white threading.
Analyze how long the larvae stays on the screen. Caterpillars can remain in its larvae stage for at least one week to a month. The more it eats, the faster it grows, the quicker it becomes an adult.The larvae may also move slowly to a decaying matter nearby or a plant, depending on the type of insect.