Zombie ladybird

The year 2025 could go down as a fantastic ladybird year; there were reports of massive ladybird aggregations in July, but by the end of August very few were still about. Then I found some Seven-spot ladybirds (Coccinella septempunctata) in our sweetcorn plants perhaps attracted by the cobs’ aphids.

One of the ladybirds caught my eye because it wasn’t moving, just twitching its legs. It was a zombie ladybird body-guarding the cocoon of a tiny wasp: Dinocampus coccinellae. It was an excellent safe place for the wasp to pupate because ladybirds give great protection against predators with their warning colours and also release defensive chemicals with their legs. But more about the wasp’s bizarre behaviour later.

In general, after the wasp emerges most of the ladybirds die; but in some cases, the ladybird recovers and may walk away. So, I kept this ladybird to see what would happen next.

The wasp left its cocoon 11 days later, headfirst. Note in the next two photos the exit cap in front of the cocoon; plus a little lump the same colour as the cocoon, possibly voided by the ladybird. It was already present in the first photo, now it is in better focus. The interesting thing is that normally ladybirds’ faeces are dark and sticky. However, I couldn’t find anything about the faeces of parasitised ladybirds.

The wasp was a female quite a bit smaller than its host. Apparently, most of the wasps are female.

This lively female wasp was a challenge to capture on camera. Below is my best shot, taken just before I released her in the garden.

Alas, the ladybird never recovered the use of its legs.

However, some years ago I kept a zombie Seven-spot ladybird that walked away after the wasp emerged - albeit slowly as it was very feeble. The interesting thing was that, in such a confined space, the wasp lost no time to attack the ladybird.

Here’s a picture, you can also watch the video.

Apparently, the females can reproduce parthenogenetically (without mating) soon after emergence.

So what is going on?

Wasps are carnivorous and extremely diverse; a rough estimate is over 500,000 species. The well-known yellow-and-black picnic wasps are eusocial and live in big paper nests (I have written about a that); but many species are solitary; other species have branched out to parasitism, and this is the case the of D. coccinellae, which has evolved a very complex relationship with the ladybirds.

A female starts by piercing the soft parts of the adult’s body with its ovipositor and lays just one egg; the larva develops inside the ladybird and when it reaches maturity bites its way out of the host. At the same time, a virus carried by the wasp’s egg manipulates the behaviour of the ladybird paralysing it in such a way that from then on its legs can only twitch (Dheilly et al, 2015).

Once outside the larva (now called prepupa because it has stopped feeding) spins a cocoon with labial secretions under the protection of the ladybird’s legs and pupates inside it. Soon after emergence the adult wasp will seek ladybirds to lay their their eggs, singly. The life cycle takes approximately 32 to 38 days from egg to adult.

This wasp is attracted to several types of ladybirds, including the introduced Harlequin Ladybird, but the Seven-spot ladybird seems to be one of its favourite hosts. Below is a diagram illustrating its life cycle when exploiting a spotted ladybird Coleomegilla maculata (Maure et al., 2014).

Conclusion

By the beginning of October ladybirds were either foraging on ivy flowers, the last food source for a lot of insects, or were getting ready to hibernate. Hopefully the wasp that I released in the garden was able to seek at least one host for its eggs, before it died. If so, its progeny will hibernate in the immature stage inside the infected ladybirds and the cycle will continue hand-in-hand.

As we have seen ladybirds, the gardener’s best friend, have an enemy - a tiny wasp endoparasitoid wasp, which in turn has an enemy: Gelis agilia - an even smaller hyperparasitoid wasp that mimics ants. Think of Russian dolls.

Further reading

Endless Forms - Why We Should Love Wasps by Seirian Summer: a really good read about the way in which wasps have evolved the most extraordinary tricks.

Acknowledgements

I’m grateful for discussions with David Notton. Also to my son Peter for giving me Seirian Summer’s book.