The bright yellow insects clustering on your milkweed are oleander aphids (also called milkweed aphids), and the most effective way to remove them is by squishing them with your fingers and rinsing the plant with water. But if you’re growing milkweed for monarchs, every removal method requires one critical first step: checking for monarch eggs and caterpillars before you do anything.
This matters more than you might think. Research published in PLOS One found that monarch butterflies lay three times more eggs on aphid-free milkweed than on infested plants. Larvae raised on aphid-free milkweed consumed and weighed twice as much as those fed infested leaves. Aphids don’t just look bad; they reduce nitrogen content in the plant and trigger defensive chemicals that make the milkweed less nutritious for caterpillars.
Know What You’re Looking At
Oleander aphids are hard to miss. They’re small, soft-bodied, and bright yellow with black legs, antennae, and two small tubes (called cornicles) on their rear end. They cluster on stems, leaf undersides, and especially around flower buds, piercing the plant tissue and sucking out fluids. You’ll often see them appear in dense colonies that seem to explode overnight.
Before removing anything, look carefully for monarch eggs. They’re tiny, pale, and oval, usually deposited singly on the underside of leaves. They can be tricky to distinguish from aphids at a glance, but eggs are smooth and stationary while aphids have visible legs and will move when disturbed. Caterpillars of any size are easier to spot with their black, yellow, and white stripes.
Squishing by Hand
The simplest and safest method is to crush aphids between your fingers. Wear gloves if you prefer, because it gets sticky. Run your fingers along the stem and over leaf surfaces, pressing aphids as you go. This is the approach recommended by the Monarch Joint Venture and multiple university extension programs because it gives you the most control over what you’re touching and lets you work around any eggs or caterpillars you find.
After squishing, you can rinse the plant gently with water to wash off the dead aphids and residue. Some sources suggest using a strong water spray to knock aphids off, but SDSU Extension specifically cautions against high-pressure water because it can also dislodge monarch caterpillars. A gentle rinse after hand removal is safer than relying on water pressure alone.
Alcohol Solution for Heavy Infestations
If aphids have overtaken all of your milkweed and hand-squishing isn’t keeping up, a diluted alcohol spray can help. The Alabama Wildlife Federation recommends this mixture in a 16-ounce spray bottle:
- 14 oz water
- 1 tablespoon liquid soap
- 1 tablespoon rubbing alcohol (isopropyl)
- 1 tablespoon vinegar
Hold the plant steady with one hand while spraying to prevent stem breakage. Before spraying, relocate any caterpillars to clean milkweed or bring them indoors to raise separately. This is not optional: the alcohol solution is lethal to monarch eggs and small larvae.
If you find eggs near aphids and can’t move them, skip the spray bottle in that area. Instead, dip a cotton swab in rubbing alcohol and dab individual aphids. It’s tedious, but it lets you kill aphids within millimeters of an egg without harming it. Just be careful not to touch the egg itself.
Attracting Natural Predators
Lady beetles, lacewing larvae, hover fly larvae, and parasitoid wasps all feed on aphids. Encouraging these predators in your garden provides ongoing control without any risk to monarchs. You can support them by planting a mix of flowering plants that bloom at different times (dill, fennel, yarrow, and sweet alyssum are good choices), avoiding broad-spectrum pesticides, and leaving some leaf litter or mulch where beneficial insects can shelter.
Natural predators won’t eliminate a heavy infestation overnight, but they keep aphid populations in check over the season. If you see lady beetle larvae on your milkweed (they look like tiny black and orange alligators), leave them alone. They’re doing the work for you.
Why You Should Never Use Pesticides
Insecticidal sprays, even organic ones like neem oil and pyrethrin, kill caterpillars along with aphids. The entire point of growing milkweed is typically to support monarchs and other pollinators, so pesticide use defeats the purpose. Systemic insecticides are even worse because they’re absorbed into plant tissue and persist for weeks, poisoning any caterpillar that feeds on treated leaves.
Keeping Aphids From Coming Back
Aphids reproduce without mating, and a single female can produce dozens of live young in a week. Complete eradication isn’t realistic. Instead, aim for management. Check your milkweed every few days during the growing season and squish small clusters before they become large colonies. Early and frequent intervention is far easier than dealing with a plant that’s completely coated.
Avoid over-fertilizing your milkweed. Aphids are drawn to plants with high nitrogen levels in their new growth, and milkweed is a native plant that generally thrives in lean soil without supplemental fertilizer. Planting native milkweed species rather than tropical varieties also helps, since native species tend to go dormant seasonally, which breaks the aphid cycle. Tropical milkweed (Asclepias curassavica) stays green year-round in warm climates, giving aphid populations a permanent home.
If a plant is severely infested and no monarch eggs or caterpillars are present, you can cut it back to a few inches above the ground. Milkweed is resilient and will regrow from the roots, emerging fresh and aphid-free. This is often the fastest reset when a colony has gotten out of control.