Know your enemy – the munchers

Short version:

I’d say avoid this one if squeamish. It’s a slightly different look at a couple of the pests you can get in the garden. You may find that it’s a good idea to let certain caterpillars (and possibly even slugs) live. Meet the caterpillar zombies that care for the parasitic wasp and the predatory slug… and just when you thought slugs couldn’t get any grosser…


We love beautiful butterflies with their pollinating loveliness, but we hate caterpillars and their vegetable destructiveness. Unfortunately, one cannot exist without the other. In lock down they became a source of home edu-tainment.

I don’t use pesticides, so I often find batches of caterpillars in the garden. They are usually cabbage white caterpillars. They come in 2 types. The smooth green cabbage white ones often get put into a dish and left on the table for the robins. The spikey other ones don’t get eaten by the birds, so they are often chucked in the bin. Sometime I keep eggs in case they are something that eats other bugs – like ladybirds.

Little one followed me around the garden during much of the beginning of lock down and because she knows that caterpillars turn into butterflies, she begged me to let the caterpillars live. I couldn’t really let them go free, so instead they became pets. They were put into a very large glass vase and then sealed loosely with a bit of card. They were given the half-eaten leaves to finish off and then given a clean and the leaves that didn’t look so appetising to humans every other day. This was my compromise. They got to live, but they weren’t free to nibble holes in the best-looking leaves willy nilly. After about a week we discovered that one had turned into a chrysalis and a couple had turned into something else. A quick hunt through the internet informed us that the tiny yellow cocoons next to the caterpillars were in fact parasitic wasps. These wasps lay their eggs under the skin of the caterpillar. When the eggs hatch the grubs grow and then chew their way out of the caterpillar. They spin their cocoons and the caterpillar spends the rest of its life as a zombie nanny. It protects the wasp cocoons and forsakes eating. We were expecting to teach little one about the life cycle of butterflies in greater depth – but got something much more eye opening.

We waited a couple more days till all the caterpillars reached their inevitable conclusions. Out of 10 caterpillars, 7 had become zombies and 3 had become chrysalises. We placed the zombies and their charges back into the garden and cleaned the vase again and put the chrysalises back inside.

We waited almost 2 weeks before the first butterfly emerged. Unfortunately, the sides of the vase were too slippery for it to climb up, so the end of its wing was touching the bottom of the vase and dried a little crumpled. We assume that it became bird food as it wasn’t a great flier. We put a selection of twigs inside the vase and the next day the other 2 emerged and climbed up the twigs to air their wings. Little one released them a few hours later. 

So… we’ve learnt a few things. If 70% of the caterpillars that are in the garden become hosts for their predators then maybe we should let them live and then the next cycle there will be more of these predatory wasps available to keep the caterpillar population down. In nature it’s all about balance. It’s not easy to tell from looking at a single caterpillar if they are carrying the wasps, but if a caterpillar looks much chubbier than its cohorts then it may be a host. The chrysalises do fine on the bottom of their ‘cage’ but there needs to be something the new butterfly can climb up high enough for its wings to fully extend. Now that we have a system and need something to keep lockdown little one entertained (and also to teach a bit of compassion as we don’t want her to go around thinking it’s OK to kill things just because we don’t like them) the capture and contain method has been deployed 3 times in total. Twice there were some zombies, but our 2 peacock caterpillars both survived to butterfly-hood.  

If you do decide that you’d like to keep caterpillars, don’t keep any of the furry ones (spikey ones are OK). Their hairs can cause respiratory problems or skin irritation if touched. They end up turning into moths anyway.

Slugs and snails

Slugs and snails are evil. As an edible gardener I find it hard to find anything redeeming about them. This year they have destroyed beans and peas by chewing through the stems by the soil, they have completely gnawed most of my aubergine plants down to a single stalk, they’ve eaten a good portion of the courgette leaves and the brassicas don’t stand much of a chance.

They are, however, grossly fascinating creatures. From what I’ve read it seems that slugs have evolved from snails, which seems illogical. You would have thought that slugs came first and then evolved a shell to protect itself. Apparently not. Slugs may not have that instant protection of being able to curl up inside a shell, but they can, without an attached cumbersome fixed shape squeeze themselves into any tiny crevice which provides all the protection they need. They don’t require large amounts of calcium carbonate or need to expend energy in having to build the shell either. They then don’t need to expend even more energy in having to bear this constant load.

Slug and snails are also incredible reproducers. They carry both sperm and eggs and when they mate, they fertilise each other’s eggs. This means double the amount of offspring from a single coupling. I was hideously mesmerized when I found this pair mating. From later research I found that the white thing you can see is in fact their huge penises (a word I never expected to write when I started this blog). I really didn’t want to touch them. Slugs are already slimy and icky.  With the added grossness of the horizontal tango it was more than I could take. Unfortunately, by the time I had returned with an old bag to scoop them up into and dispose of them, they had disappeared. I’m sure by next week, when the garden is overrun by the slippery buggers, I’ll be cursing my squeamishness.

Well, I guess I can comfort myself with the knowledge that despite them being a giant pain in the brassicas, they do at least clean up dead matter and debris and aid in decomposition. They also provide food for other creatures. Failure to dispatch is maybe a little like stocking the larder for the amphibians, hedgehogs and birds. However, that won’t stop me from heading out after a rain with a jar and a pair of disposable chopsticks to hunt them down. Judging from the leaf devastation out there, there are not enough predators to keep the gastropod population down. I won’t use slug pellets, these are terrible for the food chain. You can see more info in this post about pesticides.

One last consideration is that I’ve heard that there are some gastropods that are great predators, though these ones tend to live in the sea rather than on land. The leopard slug reportedly will eat other slugs. Unfortunately, when there are no other suitable foods, they will wreak havoc on the plants.

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