Don't let the name worry you — parasitic wasps are tiny, stingless and completely harmless to you, but they're a nightmare for garden pests. They lay their eggs in or on pests like aphids and caterpillars, and the young wasps finish the job from the inside out.
What they do
They parasitise aphids (leaving swollen, papery “aphid mummies”) and caterpillars. If you see a caterpillar with a cluster of little white rice-like cocoons on its back, leave it — it's already been dealt with, and you're about to get a fresh batch of wasps.
How to spot the signs
- Bloated, bronze or papery aphid “mummies” among a normal colony.
- White, rice-grain cocoons on a caterpillar's back.
- The wasps themselves are usually too small to notice — which is fine, they're busy.
How to attract and keep them: The adults feed on nectar from small, open flowers, so dill, coriander, fennel and alyssum keep them around. Plant a variety of flowers among your veggies (see our companion planting guide), go easy on sprays that kill the good bugs along with the bad, and leave a shallow dish of water out in hot weather.
These are the reason we go so easy on sprays — a single blast of broad insecticide wipes out an army of them. For the full approach, see our guide to managing pests the safe way.
Image: Lindemom1, CC BY-SA 4.0, via Wikimedia Commons.
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