When small, unusual deposits appear on a window screen during warmer months, the immediate thought is often that a pest has moved in. These strange-looking dots or clusters are a common sight that prompts many to wonder what insect is choosing this surface for reproduction. This information identifies the insect responsible for these deposits and explains why it selects this unique location, providing a clearer understanding of this frequent summertime observation.
The Green Lacewing and Its Stalked Eggs
The insect responsible for the distinct, small eggs found on window screens is most frequently the Green Lacewing, a delicate creature known scientifically in the family Chrysopidae. The adult insect is typically pale green, about a half-inch to three-quarters of an inch long, and features four large, translucent wings with intricate, lacy venation. They also have an unusual characteristic: prominent, often metallic-looking, copper or golden eyes.
The identifying feature of the Green Lacewing is its unique egg-laying method, which distinguishes its clutch from almost all other insects. The tiny, oblong eggs are not laid directly on the surface but are individually placed at the tip of a fine, hair-like silken stalk, which can be about a half-inch long. A female will lay these eggs singly or in small groups, with each egg on its own separate filament. This stalked placement is an evolutionary adaptation designed to prevent the newly hatched larvae from immediately consuming their unhatched siblings, a common behavior among many predatory insect young.
Once they hatch, the young are known as “aphid lions” due to their predatory nature. The larvae are grayish-brown, resemble miniature alligators, and are equipped with large, sickle-shaped jaws. These larvae feed for two to three weeks before pupating, making the Green Lacewing a beneficial insect in gardens and agricultural settings.
Common Look-Alikes Mistaken for Eggs
While the stalked appearance is a definitive identifier for lacewing eggs, other debris and insect deposits can be mistaken for them. Moth eggs are a common look-alike, but they are generally laid in tightly packed, yellowish or brownish clusters that sit flush against the screen surface. They lack the fine, hair-like stalks characteristic of the lacewing’s clutch.
Another item often mistaken for eggs is the ootheca, or egg case, of a Praying Mantis. Mantis oothecae are much larger, featuring a distinctive foamy, hardened texture that resembles dried spray foam insulation. These large cases are usually attached to plant stems, fence posts, or siding, not the fine mesh of a window screen. Non-insect deposits like pollen or dust can also collect on the screen, but these are easily wiped away and lack the uniform, oblong shape and structure of true insect eggs.
Why Screens Are Chosen and Their Role in Pest Control
The adult Green Lacewing is attracted to the window screen because of its proximity to an outdoor light source, as the adults are nocturnal flyers. The screen provides a stable, vertical surface that the female insect can easily cling to while laying her eggs. The woven texture of the screen mesh offers a suitable anchor point for the delicate silk stalks, ensuring the eggs remain suspended until they hatch.
The presence of lacewing eggs is generally a positive indicator for the surrounding landscape, suggesting the adult female detected a nearby food source for her offspring. The emerging larvae are generalist predators that feed on a wide variety of soft-bodied garden pests, including:
- Aphids
- Mealybugs
- Spider mites
- Thrips
- The eggs of pest moths
A single larva can consume hundreds of aphids during its short developmental period, making it a natural form of pest control.
Cleaning and Discouraging Future Egg Laying
If the eggs are found in an undesirable location, such as on a frequently used window, removal can be done safely without chemicals. The simplest method involves using a soft-bristled brush, a piece of tape, or a dry sponge to gently dislodge the eggs and their stalks from the screen mesh. Following this, the area can be wiped down with a solution of mild soap and water to remove any remaining residue.
To discourage adult lacewings from choosing window screens for future egg-laying, modify exterior lighting. Since the adults are drawn to light, switching exterior bulbs to yellow-spectrum or sodium vapor lights can reduce their presence near windows. Periodically spraying the screens with a light stream of water can also remove recently laid eggs and make the surface less appealing to adults seeking a stable place to deposit their clutch.