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.


Short version: I’m not here to condemn anyone who uses pesticides, as I’ve used them in the past and still use ant bait, but I’ve come to the conclusion that pesticides are terrible for the wildlife in the garden and when it comes down to it they don’t work that well in the long run. Caring for the wildlife in your garden allows creatures to do the job for you and also cares for the pollinators. Encourage small birds, hedgehogs, amphibians and predatory insects. Try other methods like picking infested leaves when harvesting, hunting for pests after dark, traps and cloches.

I have waged a constant war against ‘pests’ in my garden and I’m not slowing down in 2020. I’m afraid I’m not nice. I found a collection of about 30 tiny snails huddled up round the rim of a pot yesterday. They were so tiny and cute. I had to remind myself that they will very quickly become gooseberry sized monsters with voracious appetites. I squished as many as I could find. I then found a load of eggs a little later. I strongly suspected them to be snail eggs, but there is a possibility that they may be worm eggs. The internet failed me. There were matching pictures under both snail and worm egg searches.

Curiosity has gotten the better of me and I have contained them and will check weekly to see what happens. To be honest you can’t worry too much about this kind of thing. There’ll be plenty of snail and worm eggs in the neighbours’ gardens and in soil I haven’t dug. There’s only so much you can control. I took comfort in knowing that I had just removed about 30 definite snails less than 20 mins earlier.

Using Pesticides

Now I would be a hypocrite if I said that no one anywhere should use pesticides. I have used pesticides in the past. I don’t anymore (except for ant bait because we have evil bitey red ants) and I wouldn’t like to guarantee that I won’t use more pesticides in the future. It’s hard to state absolutes. However, I have concluded that you are better off trying your best not to use pesticides. It’s partly for the environment, but it is ultimately for selfish reasons. They just aren’t worth using. If you are on the fence or fond of using pesticides, then I hope to offer some thoughts.

The problems

Food chains and webs

So, those who remember GCSE biology might remember how energy is consumed up a food chain. This is a chain that would be quite realistic in our garden.

Sun –> kale –> caterpillar –> robin –> neighbour’s cat

Poisons tend to accumulate up food chains. Organochlorides (used in pesticides in the 1960s) were found to be the reason for death in birds of prey. Small birds were eating the poisoned pests. The predator birds were eating the small birds and the accumulation of the pesticides were killing the birds of prey or affecting their ability to reproduce (source).   

One can assume that many of the smaller birds which weren’t being eaten were also dying. From an ecological point of view this is terrible, but also from a gardener point of view you’ve lost a useful ally that was merrily eating your pests daily.

Taking it back to my garden food chain – yes, the caterpillars drive me mental, but if I poisoned them, they in turn would poison the robins, which would then poison the cats. I don’t like the cats eating the birds and I don’t like the cats poo-ing in my garden, but I certainly wouldn’t want to poison them.

By killing robins, there’ll be less robins to eat the caterpillars.

Predator – prey interactions

Another GCSE Biology topic. When left to its own devices, nature has her own way of controlling populations. E.g. aphids and ladybirds can have intertwined population cycles.

Let’s start with aphids. Let’s say that there is a huge population of aphids. This means that there is a large amount of food available to ladybirds. This means that the ladybird populations thrive and increase. The larger number of ladybirds means that there are more predators to eat the aphids. This means that the population of aphids decrease and there will be more competition for food. At some point the population of aphids will be too low to support the large population of ladybirds. This means that the population of ladybirds will decrease from lack of food and increase of competition. The decrease in population of the ladybirds means less predators for the aphids so their numbers then increase… and we are back to the start of the cycle.

Basically, nature will even out the odds. You may kill off the pests, but you may also be hurting their predators too that were helpfully gobbling them up. Chances are you will find that your pests will be back as it’s impossible to eradicate every last one (certainly not from other people’s gardens too), so the cycle continues in its never-ending loop. You might find that the predator populations affected don’t recover as quickly, giving you a bigger problem later. Why battle the inevitable by introducing harmful chemicals?

Targeting your destruction

In addition, some pesticides will hurt bee populations and other pollinators, like hoverflies, that are essential for pollination. No pollination means no fruit. Don’t forget fruit also includes things like tomatoes, aubergines, courgettes, cucumbers and the plethora of other squashes. There are bee friendly pesticides out there but there have been studies on how a cocktail of ‘non-toxic to bee’ chemicals have been killing off populations (source 1, source 2).

As a last, but rather important note. I also don’t want to kill my child as she grazes unashamedly on all my berries and salads.

Some options

Yes, it all sounds like doom and gloom but there are other options. These are some things that I’ve tried with varying degrees of success.

Harvesting pests

This is the most effective one for aphids and caterpillars and has the added advantage of real time results. Pick the most affected leaves for dinner and then soak them in salted water for 10 mins then rinse until clean. This removes the pests from the garden and washes them down the sink without introducing poisons. Anything too gross to consider eating can be put into the bin (not compost). 

I like to grow things that you pick regularly from over a long season e.g. perennial kale that you can pick from all year round, or chard that you can pick for about a year before the plant needs to be replaced. If you’re harvesting from the plants at least once a week (it can be every day in the summer) then you’ll see all the signs of pest damage and can deal with it quickly.

The night hunt

I also like to go ‘hunting’. There is an instinct in many humans to go forage, gather and hunt. There’s no reason why we must go after animals as sport, there’s plenty of satisfaction in going out just after dark (when leaf chomping pests are very active) with a pair of disposable chopsticks and an old jar and capturing slugs, snails and moth caterpillars by torch light. It’s sounds rather disgusting (and it is) but it is also incredibly satisfying. What you do with them after is entirely up to you. I have drowned them and then left them outside to be eaten (or decomposed) or sealed them in a bag and chucked them into the bin. I told you I wasn’t nice.

The large snails were apparently introduced to Britain by the Romans as food. You could ‘clean’ the snails by feeding them on safe leaves, such as lettuce, (as they accumulate toxins from the plants that they feed on) for a few days and them eat them as escargot, but I’m afraid that is currently a step too far for me. Maybe do some research on this first – please don’t poison yourselves.

Encouraging natural controls

Looking back at the food chain, and the bigger food webs you can see what predators are suitable for your needs and either encourage them into your garden, or even buy some to release.

BIRDS: Encourage small birds into your garden with bird feeders, water trays and some cover, like bushes and trees. You can also plant some bushes with overwintering berries. The trees we added were fruit trees, which are not yet big enough, but some day they’ll provide useful shelter. If you provide nesting conditions you may be rewarded with extra ravenous chicks to eat bugs. Many of the garden birds will happily eat the caterpillars and snails. Even some birds with seed-based diets, like finches, will happily eat aphids for you. Some of the birds may also eat some of my berry harvest but so far, they haven’t been a problem and I wouldn’t begrudge them some as a thank you for eating the pests. If it becomes too much, then I can also use netting to protect the berries. My mum finds that wood pigeons (who don’t really eat insects) are a pest in her garden, eating the young brassica seedlings, but this is also easily solved with a bit of netting.

AMPHIBIANS: Frogs and toads don’t need a pond to make a home in your garden. They only need one for breeding. In our rainy UK weather, our garden seems to have enough damp, as there has been many a frog sighting in the past year. You will need to eliminate chemicals, especially slug pellets. It’s not just what they’re eating, but amphibians have semi permeable skin so even exposure to spraying is harmful. You can also provide places for them to hide, such as an upturned pot with a gap at the bottom or areas of long grass for them to hide in. They love hiding behind the clutter around our waterbutt, in our unkempt grass edges, under the rosemary bushes or behind the Chinese chive patch.

HEDGEHOGS: I’m not entirely sure if we’ve had a hedgehog, but I saw a poo that I really hoped may have been from a hedgehog. I don’t even know if there are any in our area as there are many foxes and cats about. If you have a fenced garden, providing a gap at ground level for them to get in can help. You can provide a hibernating spot with a pile of logs, pile of dead leaves or a compost heap (or even a special hedgehog house). Just be careful if you do clear up piles of leaves or turn your compost. Slug pellets are also terribly bad for them, so another good reason to avoid.

BENEFICIAL INSECTS: The main thing is by avoiding pesticides you protect the beneficial insects. It’s then worth encouraging predatory insects like ladybirds and lacewings by providing somewhere to overwinter. You could investigate a bug hotel of some sorts but do some research into the type of insects you are looking to attract and what they need. Apparently, some of the ones on the market look good but aren’t very functional. They will also need some maintenance and need to be kept in shady, sheltered places. I have picked off ladybird nymphs from roadside trees and put them in the garden in the past. I don’t know if they stayed.

Ladybirds eat spider mites. Spider mites cause most damage when the weather is hot. They do less well in rainy periods. They do respond to pesticides, but then you’ll kill the predatory insects too. In the past I’ve controlled these very effectively by removing all the affected leaves and spraying the plant well with a hose and then spraying with a solution of rosemary oil and water which is said to discourage the mites without harming their predators.

There are also a host of specific parasitic creatures you can buy to target a particular problem. We had a ridiculous amount of whitefly one year and bought sachets of Encarsia Formosa, which is a tiny (smaller than a millimetre) parasitic wasp that lays eggs in the scales of the whitefly. They are really only for use in a greenhouse where you can keep the population captive and protected, but we used them outside, and they were still fairly effective.

The damage to this leaf has been done by a leaf miner which is the larvae of a fly. Pesticides wouldn’t have been much use here anyway as the pest is protected by the leaf. Either a pesticide that is absorbed by the plant (possibly making it inedible) is required, or spraying needs to be timed for when the larvae has turned into a fly and emerges. For leaf miners there is a parasitic wasp you can buy but it’s easy enough to remove and bin affected leaves.


You can buy sticky traps for things like whitefly or you can make a slug trap out of an old plastic bottle and some beer. I’ll do a proper post on this to put in the ‘things to do’ section.

Copper Tape

You can buy copper tape that you can stick around pots under the rim. It supposed to work as a barrier that slugs and snails can’t cross as their mucus reacts with an unpleasant feeling. Apparently it need to be fairly thick to be effective or they stretch across. Also be aware that the adhesive sometime is a bit poor. We’ve used these on pots and they seem to be effective. It’s hard to tell though if the plants in those pots would have been fine anyway. There’s plenty of other things they can eat in the garden without having to climb a pot. If the copper is even slightly unpleasant for them they could probably go elsewhere.


Yes, creatures have got to eat, they’re only doing what nature intended them to do. I would just like them to stick to eating a whole leaf at a time and not leave leaf doilies, or could they wait till a plant has grown lovely and big. They could have tender tips then. I wouldn’t mind so much. The frustration of a seedling eaten across a stem or an asparagus tip nibbled to death before it can fulfil it’s slender juicy destiny is the original reason I used to use pellets.

Cloches made out of old bottles have become my go to now for precious seedlings. Alternatively, plant for redundancy. Assume that a few of your seedlings won’t make it and plant a few more.

So… I’m just hoping to encourage the use of methods other than pesticides in the garden. If you have any helpful hints or anything that worked especially well for you, please feel free to share in the comments.