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Ladybugs and other Beneficial Insects; Get Good Bugs to Eat Your Bad Bugs!


Q. Dear Mike: Several years ago, someone told me that ladybugs and Praying Mantis were good for the garden. Is this true? If so, please tell me where to buy them. Thanks.

    ---Dave in Chestnut Hill, PA
A. We get this question a lot, Dave. The wonderful insects that dine only on landscape pests and don't harm good bugs or plants are called 'beneficials', and ladybugs definitely fall into this category—but not the way many people think.

The spotted red 'ladybug' we all know so well (more correctly called the 'lady beetle' or 'ladybird beetle', as these insects are true beetles and not bugs) does dine on the occasional aphid and other soft-bodied pest, but like many insects, it doesn't really eat all that much in it's adult form. It's the ladybug's larvae that are voracious predators of soft-bodied problem insects, especially aphids. Gardeners plagued by those sap-sucking perfidious pests (i.e. rose growers) should become acquainted with the appearance of this beneficial ladybug baby; otherwise, they might try and kill the spiny, scary-looking, alligator/dragon-like things!

And you can buy ladybugs mail order. But its important to release them correctly or they will all fly away. Although there are hundreds of different types of ladybugs—including one that's blood red with no spots and a tiny one that's jet black—you only see the basic "Convergent Lady Beetle" (Hippodamia convergens) offered for sale to homeowners. These are collected from winter hibernation sites (and yes, it's fine to do so; this has been going on for many decades without any negative impact on their population).

When they arrive, the ladies must be released in the evening into a soaking wet garden that has some aphid problems.

Release them during the day and they will all fly away.

Release them into a dry garden and they will all fly away.

Release them into a garden with no aphids for their babies to eat and they will all fly away.

But they won't fly in the dark, so releasing them just after sunset insures they'll stay the night. They're dehydrated when they arrive, so a garden that you've made soaking wet before their release will provide many opportunities for them to quench their thirst and thus make them feel that this place has some promise. And if they encounter aphids as they're drinking and checking it out, many of the ladies will decide that this garden is a good place to spend the summer. Just be nice to those scary looking babies and don't destroy their eggs, which are yellowish-orange ovals laid on the undersides of plant leaves.

You can also attract local ladybugs—and lots of other beneficial insects—with a three-pronged method.

  1. Don't use chemicals of any kind in your garden! (I love saying that!)
  2. Provide appropriate water sources by filling saucers with pebbles and water. The tiny insects can perch on the pebbles and get a drink without fear of falling in and drowning, as they could in a big birdbath.
  3. Grow plants whose small flowers produce pollen and nectar that the adults can easily get to for a little sugar rush.
Planting twice as many culinary herbs as you need for cooking is a great way to achieve #3. Continually pinch back and harvest half the plants to prevent them from flowering, just as you normally would for kitchen use (when herbs are allowed to flower their taste often changes, and always for the worse), but allow the other half to produce the small flowers that are so inviting to beneficials. Dill, fennel and caraway are the absolute best choices; also especially attractive are cosmos, marigolds, and tansy (that's the herb Tanacetum vulgare, not the noxious weed called tansy ragwort; see our previous Question of the Week on ants for more about this fascinating and useful plant).

This plan will also bring in many other beneficials. Like the beautiful lacewing—a delicate looking flyer whose babies are very similar in appearance to ladybug larvae, but are even better at chowing down on those perpetual pests of roses and other plants; so much so that their common name is the 'aphid lion'! You'll also attract Braconid, Trichogramma and other mini wasps. So small you can barely see them, these tiny creatures ignore humans, and lay their eggs inside or on top of pest caterpillars, parasitizing and killing them and, of course, breeding more caterpillar-controlling wasps. (Those white 'spines' you often see on tomato hornworms are Braconid wasp eggs).

Lacewings and mini-wasps can also be purchased mail order with very good results. Generally shipped in the egg stage, you place the little containers in a shady protected spot in the garden. Adult wasps will emerge to do their caterpillar-controlling thing; and those aphid lion lacewing babies will hatch and go looking for aphids. (Obviously, locate their containers near the plants with those problems; remember—they need some pests to prey upon to survive!)

That water, pollen and nectar will also bring in other beneficial insects, like damsel bugs, big-eyed bugs, minute pirate bugs, assassin bugs (which attack adult Japanese beetles!) spined soldier bugs, syrphid flies (which look like bees, but hover like hummingbirds!) and tachnid flies. Go online and become familiar with the appearance of these creatures; otherwise you might try and kill your spined soldier bugs, which look a lot like stink bugs (the good guys have sharply pointed shoulders) or tachnid flies, which closely resemble houseflies (the good guys have bristles, and fly in a very un-housefly-like manner).

And what about the fabled praying mantis? These creatures are amazing, but aren't truly beneficial, because they'll eat any insect they can catch, including good ones. Now, if a few appear in your garden, let them be; they're part of the natural world, fun to watch, won't harm your plants and will kill some pests for you. But I strongly recommend against purchasing them mail order; many researchers feel that those non-native mantises will attack and kill the native species when they are released.

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