Beneficial insect
Braconid wasp
Tiny, stingless wasps that turn hornworms and aphids into nurseries.
Too small to sting you. Most are smaller than a grain of rice.
How to spot it (and its larva)
These are not the wasps you fear. The garden's parasitoids are minute, often 1–3 mm, and cannot and won't sting a person. You almost never see the adult. What you see is the evidence: a tomato hornworm covered in what look like grains of white rice (braconid cocoons), or a papery, bloated bronze 'mummy' where an aphid used to be.
The white rice on a hornworm is the tell most gardeners get wrong. It means the wasp has already won, so do NOT kill that hornworm. Leave it so the next generation of wasps hatches and patrols your garden.
What it hunts
The pests it clears for you. Tap any one for the full identify-and-control guide.
- Tomato hornworms: The 'white rice' cocoons mean the hornworm is already doomed, so leave it.
- Aphids: Aphidius wasps leave bronze, papery aphid 'mummies.'
- Cabbage worms: Trichogramma wasps parasitize the eggs before they hatch.
How to invite it in
You don't buy most beneficials. You build the habitat that keeps a wild population breeding on-site. Do these and they come, and stay.
- Plant tiny-flowered nectar sources
The wasps are too small for big blooms; they feed on minuscule flowers. Sweet alyssum, dill, fennel, cilantro, and yarrow are the classic parasitoid feeders.
- Tolerate the first pests of the season
Parasitoids need hosts to reproduce. If you nuke every aphid and caterpillar in spring, the wasps have nothing to lay in and never build up. A little early damage buys season-long control.
Plants and habitat that bring them in
Small-flowered plants feed the adults so they stay and breed. A packet of these does more for lasting control than a bag of mail-order bugs.
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Don't undo it
The fastest way to lose a beneficial is a broad-spectrum spray. It kills the predators faster than the pests and triggers a worse rebound.
- Killing a 'white-rice' hornworm, since those are wasp cocoons; leaving it releases dozens more wasps
- Broad-spectrum insecticides, which are lethal to the tiny adults
- Spraying aphid 'mummies'. Each bronze mummy is a wasp about to emerge and hunt
Should you buy them?
Trichogramma wasps are sold on little cards for release against caterpillar-egg pests (cabbage worms, corn earworm, borers) and can work well in a targeted release. For hornworms and aphids, habitat plantings do the job for free.
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Questions about braconid wasps
My tomato hornworm is covered in white rice-like things. Should I remove it?+
No, leave it. Those are the cocoons of a braconid wasp that has already parasitized the hornworm. It will stop feeding and die, and dozens of new wasps will hatch to protect your garden. Killing it throws away free pest control.
Will these wasps sting my family?+
No. Garden parasitoid wasps are a millimeter or two long, have no interest in people, and are physically too small to sting you. They are nothing like yellowjackets or paper wasps.
Plan a garden good bugs want to live in
PlotToTable sizes your beds, spaces every crop for airflow, and flags the pests that hit what you grow, so the predators that eat them have a reason to stay.