Inside the world of the cuckoo wasp

This blog was written by Benjamin Loon, a Bushwise Professional Safari Guide student. Each student takes a turn as camp manager, and writing a blog is part of the experience. All images accompanying this blog were captured by Benjamin.

Cuckoo wasps are small, mostly solitary wasps best known for their bright metallic, iridescent body colours, which have earned many species the common name “jewel wasps”. However, the more widespread name “cuckoo wasp” comes from their unique reproductive strategy: brood parasitism, much like that of cuckoo birds. It is this unusual behaviour, combined with their brilliant colours, that fascinated me from a young age.

The beautiful colours of the cuckoo wasp are what first drew me to them, but the reason behind these colours is just as intriguing. The vibrant, jewel-like appearance of many cuckoo wasps is not pigment-based alone, but largely structural. Their exoskeleton has a unique multilayered structure composed of extremely thin, semi-transparent layers that act as light reflectors. These layers produce vivid iridescent colours through selective interference as light hits them. Because the colours depend on the angle of incoming light, they can shift dramatically simply by changing your viewing angle.

Scientists suggest several possible reasons for this striking colouration. These include camouflage among shiny or reflective surfaces, visual signalling (including limited sexual signalling), thermoregulatory effects, or even added structural strength to the exoskeleton itself. No single explanation applies to all species, and the true function may differ between lineages. As a photographer myself, these colours make cuckoo wasps a dream subject to photograph (when they finally sit still!) and make the moment of getting the shot even more rewarding.

Cuckoo wasps practise kleptoparasitism, the theft of food collected by another individual,  as well as parasitoidism, where the parasite’s young ultimately kill the host’s brood. After a female cuckoo wasp sneakily infiltrates a host’s nest, she lays her egg in the same cell as the host’s eggs before quickly leaving the area. The cuckoo wasp egg usually hatches sooner than the host’s, and the larva consumes the food stored for the host larva (kleptoparasitism). In some cases, the cuckoo wasp larva will also eat its foster siblings (parasitoidism).

Cuckoo wasps parasitise a wide range of hosts, including many solitary bees and wasps such as mason bees, potter wasps and mud-dauber wasps. I recently observed this behaviour while sitting at a termite mound chimney, watching cuckoo wasps shadow potter wasps in an attempt to locate their nests. The potter wasps would repeatedly chase the cuckoo wasps away whenever they got too close, much like brood-host birds do when defending against cuckoos.

The interaction between cuckoo wasps and their hosts is a classic example of brood-parasitic coevolution. Host species evolve behaviours that reduce the risk of parasitism, such as sealing nest cells more quickly after laying eggs, nesting in more concealed locations, guarding their nests, or making subtle changes to nest architecture. In response, cuckoo wasps evolve counter-strategies such as stealthy approaches, rapid egg laying, repeated nest visits, and closely shadowing hosts to locate nesting sites.

Interestingly, some observations suggest that multiple cuckoo wasps may occasionally mob or distract a host wasp, which superficially resembles the distraction tactics used by some avian brood parasites. While this is not a universal or well-documented strategy across all cuckoo wasp species, it is a fascinating example of how similar pressures can lead to convergent behaviours in very different animals. Like cuckoo birds, cuckoo wasps are locked in an evolutionary arms race with their hosts – a dynamic that highlights how much complexity exists in the often-overlooked insect world.

Many physical and behavioural traits of cuckoo wasps appear to be adaptations to their risky lifestyle as nest invaders of often larger and more venomous hosts. They possess an unusually dense and tough exoskeleton that helps resist stings from angry hosts if caught. They also exhibit a unique defensive behaviour known as conglobation, where the wasp rolls into a tight ball, tucking in its legs and antennae to protect softer body parts. This combination of armour-like exoskeleton and balling behaviour greatly reduces the risk of injury during host encounters and increases the wasp’s chance of escape after laying its eggs.

Cuckoo wasps are not merely “parasites”, but important components of solitary bee and wasp communities. They influence host population dynamics, drive changes in nest architecture and behaviour, and even play a minor role as incidental pollinators when visiting flowers for nectar. Unfortunately, like many insects, cuckoo wasps face growing threats from habitat loss and environmental change. As my favourite insects, I sincerely hope their populations remain healthy and continue to delight our eyes while remaining a persistent nuisance to the local insects!

If you’d like to see the fascinating small creatures of the wild for yourself, Bushwise offers a selection of wildlife courses designed to help you turn your passion into purpose.