You would be hard-pressed to find lovelier insects than the cuckoo wasps of the family Chrysididae. They are clad in gem-like colors of emerald, ruby, jade, and even copper and gold. These wasps are small, and stingless, too, making them much less intimidating than other members of the order Hymenoptera.
The life histories of these unique insects remind one of a spy thriller or great crime caper. While a few obscure, tiny cuckoo wasps parasitize the eggs of walkingstick insects, most female cuckoo wasps lay their eggs in the nests of other kinds of solitary wasps, or solitary bees, exposing themselves to the jaws and stings of much larger, stronger species. The cuckoo wasps have what amounts to a “bulletproof vest” in their extra thick exoskeleton that acts like a suit of armor. The wasps can also roll themselves into a compact ball to protect their faces, legs, and other vulnerable body parts, much like a turtle or tortoise can retract into its shell, or an armadillo rolls up.
That durable cuticle is pitted, grooved, and otherwise sculptured, creating facets that reflect various wavelengths of light and give the insects their bright metallic colors. Pigments have nothing to do with their jewel-like quality.
Different species of cuckoo wasps have different “hosts” for their larval offspring. Some species specialize in breaking and entering the nests of mud daubers while others spy on wasps that dig nest burrows in the soil or sand. When the mother host species is away from the nest, the cuckoo sneaks in to lay her own egg. She has special, telescoping abdominal segments that complement an egg-laying organ called an ovipositor, helping her to hide her egg among the paralyzed insects or spiders harvested by the host wasp as food for its own larvae.
The egg of the cuckoo wasp hatches after the larva of the host species. The cuckoo larva then attaches itself to the host larva, and waits patiently as the host larva eats and grows, reaching the “pre-pupal” stage. At this point the cuckoo larva begins consuming the host larva, eventually killing it in the process. The mature cuckoo larva then pupates and emerges from the nest as an adult cuckoo wasp sometime later.
An alternative life history is found in some species where the cuckoo larva eats the host’s egg or young larva, then scarfs down the food stored for the host (paralyzed insects, spiders, or pollen and nectar).
Adult cuckoo wasps fuel themselves on carbohydrate-rich foods. Oddly, few species seem to visit flowers with any regularity. Instead, you are more likely to find them around aphid colonies, lapping up the “honeydew” excreted by the sap-sucking aphids as a sugary, liquid waste.
Cuckoo wasps can also be found on the exterior of old barns, on dead, standing trees, and similar situations where they hunt for the nests of their hosts.
Chrysidids are more diverse in western North America than they are in eastern North America, but are often harder to find in the west. Few resources exist to help you to identify them, either, though there is a wonderful new interactive key to Cuckoo
Wasps of Eastern North America at Discoverlife.org. The website BugGuide.net also has many images of cuckoo wasps sorted at least to the level of subfamily or tribe. The best internet resource is devoted to European cuckoo wasps and is dubbed ”Chrysis.net.
By all means, enjoy searching for cuckoo wasps in your own backyard, local parks, and elsewhere. There is still much to be learned about them and room for scientific contributions from everyone.