Out of all the enemies threatening our cannabis plants, these little insects are indeed one of the most difficult to deal with. To have a decent chance to keep them at bay, it's essential to have the right tools and knowledge. If, despite all this, you fail to protect your plants, you have to, at least, be able to react quickly. Escaping the voracious appetite of these little insects is almost impossible for they won’t stop eating whatever comes their way until they’ve eaten up all the food inside your plants.
For starters, one important question must be answered: what are caterpillars? Well… caterpillars are basically soft-bodied larvae, that is to say, very young insects that belong to the Lepidoptera family, a group of flying insects more commonly known as butterflies. There are more than 10,000 different species of caterpillars, although they all have some features in common: long, segmented bodies, six legs, and five pairs of pro-legs with small hooks. Besides, they're polyphagous, meaning they feed on a range of plants.
The life cycle of caterpillars is very simple: once the eggs hatch, they emerge and immediately start feeding on the plant nearest to them. When they reach a certain size, they enter the pupal phase, with some species sipping cocoons. After one week to one month, their metamorphosis comes to an end and butterflies or moths emerge.
The further the better
The best you can do to ward off caterpillars is to make sure they don't find any way to reach them. There are many ways you can prevent them from appearing and from making your grow their home if they finally happen to show up:
If you're growing in a greenhouse, then use a bug screen to keep butterflies and other flying insects out.
If you're growing outdoors, instead, try to use other less dangerous animals to help you out. The chances are pretty high that they'll successfully keep those unwanted visitors at bay. A widely used strategy is that of installing nest boxes for caterpillar-eating birds such as goldfinches, sparrows or robins nearby.
If you're not into birds, you can make use of caterpillar predatory insects (parasitic wasps or braconid wasps). These wasps lay eggs on the caterpillars and, once they hatch, become food for them. Besides non-aggressive towards people, attracting them is incredibly easy. All you have to do is grow some parsley or carrots near your cannabis plants and wait.
Growing other plants around your cannabis plants could also prove useful in certain cases for preventing their appearance. Thyme and basil, for example, are excellent insect repellents. Another strategy would be to grow some of their favorite plants, like cabbages or soybeans, to keep them entertained at a safe distance and prevent them from feeding on your plants. Build up different barriers by alternating the plant species to fully protect your weed.
Traps can also make great allies, the most effective ones being the pheromone traps that attract and catch males rendering them unable to attack or reproduce.
Prevention sometimes fails
If the preventive measures used so far haven't worked as you expected them to and the so-dreaded caterpillars have colonized your plants, get ready for action.
There are some telltale signs indicating the presence of caterpillars, the most evident of which being the emergence of small tear-shaped holes on the leaves caused by bites. Besides hampering the growth of your cannabis plants, these little bites can slow down their metabolic processes sometimes even leading to death. If you feel your plants are growing more slowly than they should, that could be the reason.
Another species of caterpillar known as hemp borer (Grapholita delineana), with a special liking for the stems, generally feasts on the marrow within them causing the plant to develop necrosis and, at an advanced stage, even decompose. To top it off, the little holes made by hemp borers open up the gates for all kinds of sap-sucking plagues and fungi.
Grapholita delineana. Whitney Cranshaw, Colorado State University, Bugwood.org
There are other caterpillars attacking mostly cannabis buds, the most common ones being the so-called vampire moths (Spodoptera exigua), silver Y moths (Autographa gamma) or cotton bollworms (Helicoverpa armigera). It's during the flowering stage that these caterpillars are very much likely to appear, eating up all your buds and destroying your grow right when your plants are almost ready for harvest. Any grower's nightmare.
Spodoptera exigua. Whitney Cranshaw, Colorado State University, Bugwood.org
Don't forget that caterpillars are mostly nocturnal animals that rarely come out during daytime, so they're quite hard to spot. Examine your plants closely at dusk or at dawn, which is when they leave or come back to their hiding place. Or at night even, with the help of a torch, of course.
If you've spotted the little bites but still can't find the worm-like insects, then check every part of your plants, especially the most hidden ones where light can hardly get to, like the underside of leaves or the buds. There's a pretty good chance you may come across some small black balls too. If you do, that'll mean you've found their excrements; so yes, caterpillars have settled in your plant. Pay special attention to them for these little droppings could provoke Botrytis.
No mercy
If you spot any of these symptoms, it's wartime. No regrets, no second thoughts. You have to be ready to play your cards well to beat your opponent. To help you out, we've prepared the ultimate list of weapons to treat caterpillar plagues:
This first one doesn't seem deadly but it can make a great difference: your hands. Search through the leaves, stems, buds… any corner of your plants where they may have hidden. Do so wearing plastic gloves. Remove all the caterpillars you find by hand and take them as far as you can. Or kill them.
You can also spray your plants with insect repelling solutions. Garlic, potassium soap or tobacco sprays have proved to be really effective organic pesticides. Neem oilcould work well too. Pulverize all your plants with it and caterpillars will know at once they are no longer welcome into your grow.
The third weapon seems a bit more dangerous: full-spectrum insecticides like pyrethrins. The market is full of natural and chemical insecticides that will help you find your way out of this horrible situation. They act by contact, meaning the caterpillar becomes sick and eventually dies when sprayed with it.
The fourth one involves the use of biological weapons. Bacillus thuringiensis (BT) is, without any doubt, the best anti-caterpillar remedy for, besides incredibly effective, it's harmless to people, pets, and other insects. It's a naturally occurring bacterium whose toxins cause irreversible damage to the digestive system of this kind of insects. It acts by ingestion, so with just one bite of a BT-sprayed leave or bud, the insects will stop eating and starve to death.
Our recommendation is to alternate the different strategies to guarantee the best results and obtain incredibly heavy yields.