If you're asking where do spider mites lay eggs, the answer is on the undersides of your plant leaves. Females tuck their eggs near leaf veins and inside protective webbing. This spot shields the eggs from rain, wind, and hungry predators. It also makes them very hard for you to see unless you flip the leaf over and check the bottom side with care.
I first found spider mite eggs while checking my tomato plants with a 10X hand lens. Tiny round spheres sat in neat rows along the midrib vein on the leaf's underside. Each one measured about 0.14 mm across, barely visible even with the lens. They looked like tiny clear glass beads lined up in a neat row. Without that hand lens I never would have spotted them at all.
The numbers behind spider mite eggs are what make them so dangerous to your plants. Ohio State reports that one female lays 5 to 6 eggs per day and can produce over 100 eggs in her lifetime. Colorado State puts the count even higher at about a dozen eggs per day for a couple of weeks. Those eggs hatch in just 3 to 5 days when your garden is warm. One female you miss can start a full colony on your plant in under two weeks of good weather.
Fresh spider mite eggs are round and clear when you first see them. UC IPM notes that they darken as the mite inside grows closer to hatching day. By the time an egg looks dark, it's about to pop open. This quick cycle means new mites pour onto your plants every few days during warm weather. Each new female starts laying her own eggs within about a week. That kind of spider mite reproduction creates a growth curve that gets steep fast if you're not paying attention to your plants.
You should check your plants for eggs at least once a week during the growing season. Flip leaves over and look near the main vein where females like to lay. If you see clusters of tiny round dots, you know the colony is active and growing. Catching eggs early gives you a chance to act before the next generation hatches and spreads to your other plants nearby.
To target eggs on your plants, you need to spray the undersides of every leaf where they hide. Horticultural oil is your best choice for egg kill because it coats and smothers them on contact. Insecticidal soap only kills mites it touches while they move around. Soap can't harm eggs since they just sit there without moving. Spray oil every 5 to 7 days for at least three rounds so you catch each new wave of hatchlings before they mature and start laying their own eggs on your plants.
Knowing about spider mite reproduction helps you see why skipping even one treatment matters so much. In my experience, pruning off your worst leaves and tossing them in the trash removes thousands of eggs at once. This won't fix the whole problem on its own, but it gives your oil sprays a much smaller target to hit. Pair leaf removal with thorough sprays on what's left and you'll break the breeding cycle on your plant for good. Stay on that weekly schedule and you'll catch any new egg laying before it turns into a full blown problem again.
Read the full article: Spider Mites: Full Guide to Control
