thats not entirely true, there is a number of bugs that are carnivorous and eat aphids and other such bugs that can infest marijuana. there was this hydroponic shop near where i used to live called "be well hydroponics" and they used to sell at least 4 or 5 different kinds of bugs for gardens.
Mkay is very right... here are a few examples....
Photo: Jack Dykinga. USDA Agricultural Research Service
Most of the beautiful adult lacewings feed on pollen, nectar, and honeydew. Green lacewing larvae, however, are voracious predators. Nicknamed "aphid lions," the larvae do an impressive job of devouring
aphids by the dozens. Larvae hunt for soft-bodied prey, using their curved, pointed mandibles to stab their victims.
2. Lady Beetles
Photo: © Debbie Hadley, WILD Jersey
Everyone loves a ladybug, but gardeners hold them in especially high regard.
Lady beetles eat aphids, scale insects, thrips, mealybugs, and mites – all the pests gardeners despise. With lady beetles, you get more bang for your buck, because both the adults and the larvae feed on pests. Lady beetle larvae look like tiny, colorful alligators. Learn to recognize them, so you don't mistake them for pests.
3. Assassin Bugs
Photo: Susan Ellis, Bugwood.org
Assassin bugs know how to take care of business. These true bugs use trickery, disguises, or just plain brute force to capture a meal. Many assassin bugs specialize in certain kinds of prey, but as a group, assassins feed on everything from beetles to caterpillars. They're fun to watch, but be careful handling them because they bite – hard.
4. Praying Mantids
Photo: Flickr user Scott Robinson
Contrary to popular belief, it is not illegal to harm a praying mantis. But why would you want to?
Praying mantids can handle even the largest pests in the garden. You need a good eye to spot one, because their coloration and shape provide them with perfect camouflage among the garden plants. When the nymphs hatch, they're so hungry they sometimes eat their siblings. In fact, praying mantids are generalist predators, meaning they're just as likely to eat a helpful lady beetle as they are to catch a caterpillar.
5. Minute Pirate Bugs
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
Arrgggh. You probably have minute pirate bugs in your garden, and don't even know it. Minute, indeed – these predators are tiny! Minute pirate bugs usually measure a mere 1/16th inch long, but even at that size, they can put away a good number of aphids, mites, and thrips. Next time you're in the garden, take a hand lens and search for them. Adults have black bodies with a white chevron pattern on their backs.
6. Ground Beetles
Photo: Susan Ellis, Bugwood.org
You've probably overlooked the
ground beetles in your garden. Lift a stepping stone, and you might see one skittering away. The dark-colored adults often have a metallic sheen, but it's really the larvae that do the dirty work of pest control. Ground beetle larvae develop in the soil, and prey on slugs, root maggots, cutworms, and other pests on the ground. A few species will venture up a plant stem and hunt for caterpillars or insect eggs.
10. Damsel Bugs
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
Damsel bugs use thickened front legs to grab their prey, which includes aphids, caterpillars, thrips, leafhoppers, and other soft-bodied insects. Nymphs, too, are predators, and will feast both small insects and their eggs. With their dull brown coloring, damsel bugs blend in to their environment quite well. They look similar to assassin bugs, but are smaller.
.... anyways those are just some good examples. haha
