Cuckoo Wasp

I discovered a new insect in my garden: the cuckoo wasp.

Cuckoo Wasp on pine needle (Wasrts) CC BY-SA 4.0

I was busy planting seeds and placing them in a sunny location, on my pumpkin ladder, when a flash of metallic green caught my eye. I looked for it and couldn’t find it, at first. But I knew I had seen it and I knew that metallic green either meant an insect or some plastic trash had flown in. In either case, I had to find it.

Finally, there it was! An insect I had never seen before. It was probably no more than 1/4” long with an oblong body, a largish, rectangular head, and jointed, fringed antennae. The wings were as long as the body and when the sunlight hit it, the bright green really was beautiful. But I didn’t yet know if this was a good bug or a pest, so I captured it.

Once I had it in a container, I could see that the underside of this new insect was just as bright green as the top. But I still didn’t know what it was. ​

Underside of cuckoo wasp (Kate Russell)

​I looked in my field guide, but couldn’t find it. I could have asked my entomologist friend in Colorado, but I already owed him a batch of brownies for my last ID request, so I went to social media and asked the hive mind. In no time at all, I had several friends telling me that my new guest was a mostly beneficial insect, called a cuckoo wasp.

I say mostly beneficial because cuckoo wasps kill the larvae of other insects. Some of those other insects are pests and some of them are beneficial pollinators.

There are over 3,000 different cuckoo wasps in the world and 166 species in California. They are also known as emerald wasps, jewel wasps, ruby wasps, and gold wasps, depending on the color. These wasps don’t look anything like the yellow jackets or paper wasps most of us see each summer. They look more like harmless beetles. There is debate about whether or not these insects can sting. I didn’t see any sign of aggression in my visitor, by your experience may vary.

Ruby cuckoo wasps feed on specific wasps that feed on honey bees (Frank Vassen) CC BY 2.0

Cuckoo wasps get their name because they lay their eggs in the nests of other solitary bees and wasps. Laying eggs in a bee’s burrow is no mean trick. Female cuckoo wasps watch sawflies and other solitary bees and wasps as they drag paralyzed spiders and other insects into their burrows, stocking up a larder for their offspring. The female cuckoo waits until the host flies off before sneaking inside to lay her eggs. Research has shown that cuckoo wasps are able to mimic the smell of their hosts, rendering them invisible within the darkness of a burrow. Particularly brazen cuckoo wasps will catch a ride on the paralyzed prey, carefully staying out of sight. This is dangerous business.

Luckily for the cuckoo, if she is spotted, her brightly colored, heavily pitted exoskeleton is able to protect her from bites and stings. She is also able to curl up into a ball the same way a sowbug or an armadillo might. If she curls up inside an angry host’s burrow, the host has no other choice but to throw it outside unharmed. If you happen to spot one curled up, it may simply be taking a nap.

Sleeping cuckoo wasp (Katia Schulz) CC BY 2.0

Some cuckoo wasps are murderers and some of them are thieves. Parasitic cuckoos eat the offspring of solitary bees, wasps, hornets, sawflies, silk moths, and stick insects. The kleptomaniac cuckoos steal the food left for the host’s offspring. 

It ends up that cuckoo wasps have very specific needs, as far as habitat goes. Adults feed on nectar from flowers in the carrot family, the sunflower family, and the spurge family. Cuckoo wasps are secretive and they move very quickly, which explains why I’ve never seen one before. But I hope I see them again!