EGARDENING INDEX                  Last modified December 12, 2006

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Beneficial Bugs
by Catherine Kavassalis for the Oakville Horticultural Society

Little Miss Muffet sat on her tuffet
Eating her curds and whey
There came a big spider
Who sat down beside her
And frightened Miss Muffet away
                  Mother Goose 1916
 

... But Miss Muffet,  that arachnid is a harvestman, (Phalangium opilio to be exact), not a spider.  It has no fangs and eats many garden pests like aphids, caterpillars, leafhoppers and slugs. I suppose that it really does not make a difference to those afraid of creepy crawlers. Nonetheless, I would like to encourage you to invite more such creatures to dine in your garden. 

Most bugs do no harm in the garden. In fact, less than 1% of insects are pests to humans, and the vast majority of invertebrates are either incidental or beneficial to gardeners. Of course, we prefer the beneficial sort, but its all about balance.  A healthy garden is a biodiverse garden - rich with life. The pollinators, decomposers, predators and pests all have their place. Remember, we would have no beautiful butterflies without a few ravaged leaves. However, we like our plants to stay healthy and that means keeping the various leaf chewers, sap suckers, stem borers and root feeders in check. These pests are prey to a variety of predatory species and host to numerous parasitic ones. We just need to invite those predators and parasites to dinner.

Inviting beneficial bugs into the garden is not a new idea. In the 4th century, golden ants were sold at markets to area farmers to protect the mandarin orange trees from insect pests. Farmers even built miniature bamboo bridges to connect trees so the ants could move freely between them (Hsi Han, 304 A.D., Records of the Plants and Trees of the Southern Regions).  Today, ladybugs, lacewings, praying mantises, predatory mites, parasitic wasps and entomopathogenic nematodes are just a few of the beneficial organisms commercially sold for pest reduction. You don't need to go to such expense. Beneficial bugs abound and will come to your backyard if the conditions are right.

How do you welcome these garden helpers?

Which bugs are good bugs?

There are thousands of beneficial insects including hundreds of flies (Diptera), bees and wasps (Hymenoptera), dragonflies (Odonata), beetles (Coleoptera), mantises (Pterygota) and true bugs (Hemiptera). Though not insects, arachnids (like spiders, harvestman and predatory mites) are also beneficial for home gardens. Other beneficial invertebrates include beneficial nematodes that eat bacteria, fungi, and other nematodes. I have produced a very brief online display of a few of the most common beneficial insects that you may find in your garden and posted references for your further investigation. (Note the in-text links are from a diverse set of websites from academic to commercial from Canada to Australia. They are simply a delight of diverse information, illustrations and photographs.)

Most of you are familiar with lady bugs (Coccinellidae), although you may be surprised by the variation in the16 species occurring in Canada and their odd little alligator-like larvae. (Nature Canada posts a lady bug ID Guide http://www.cnf.ca/ladybeetle/guide.html ). Both the larvae and the adults are voracious aphid eaters. They also enjoy scales, mealy bugs, mites and various soft-bodied insects. Apparently, a combination of whey and yeast called wheast is used in insectaries to attract and feed lady beetles and other predatory insects, but most gardens have plenty of natural food for these hungry little beasts. Newly emergent adults require pollen and nectar and seem to most enjoy plants like yarrow, dill, angelica, and cilantro.  These same plants attract lacewings.

 Adult lacewings (Green Lacewings Chrysoperla and Brown Lacewings Hemerobiidae) look dainty and delicate as do most members of the Neuroptera order. Like ladybugs, adult lacewings feed on pollen, honeydew and other insects and the larvae, sometimes called aphidlions, will dine on anything from euonymus scale to leafhoppers. Some species are specialists and will, for instance, feed primarily on a particular mealy bug or a particular aphid species. To encourage lacewings to stay in your garden, give them a safe place to overwinter. You can create an artificial hibernaculum. First, cut the bottom off of a 2 litre plastic bottle. Next roll up a piece of corrugate cardboard to form a spiral resting area and insert it into a plastic bottle. Then just hang the capped bottle by a string near a house light in the fall.  Horticulture Research International have been monitoring such lacewing hotels in hop orchards and find they have been useful in maintaining stable populations of these helpful predators. (Hotel design is online http://www.organicgardening.org.uk/factsheets/gg13.php). Dustywings (Coniopterygidae) are tiny cousins of Lacewings and excellent at abating small arthropods like mites.

There are hundreds of species of ground beetles native to our region.  Some look quite ferocious and are indeed good hunters. Both the adult beetles and the larvae rove the soil in search of food. For instance, the Calosoma species (illustrated) are "caterpillar hunters" particularly fond of gypsy moth larvae. Unfortunately, spraying lawns for white grubs, decimates ground beetle populations causing an increase in a variety of secondary pest populations that would normally be kept in check by these natural predators. 

Other beneficial beetles include: fireflies (Lampyridae), which develop as predators of slugs, snails and worms; omnivorous Collops Beetles (Melyridae);  brightly checkered Clerid Beetles (Cleridae), which prey on wood-borers and bark insects; uniformed Soldier Beetles or Leatherwings (Cantharidae), which can guard against root maggots along with the oddly shaped Rove Beetles (Staphylinidae).

Whereas beetles are chewers, there are millions of so-called 'true bugs' defined by their piercing beak - good for sucking juices from a variety of sources. Although there are many members of Hemiptera that gardeners would consider pests, there are also many beneficial members of this group including: Damsel bugs (Nabidae), Pirate bugs (Orius species), Predatory Plant bugs (some in the order Miridae), Assassin bugs (Reduviidae) and Bigeyed bugs (Geocoris spp.).

Syrphid flies, also called flower flies or hover flies, are really quite lovely. Often brightly colored and striped like honey bees, these harmless, lovely species are often seen feeding at flowers. The larval stage of a syrphid is an ugly yet hardly ever seen maggot that crawls over foliage eating, for the most part, aphids. Other beneficial flies include the longlegged flies (Dolichopodidae) sometimes noted for their metallic green sheen. The adults feed on small flying insects like gnats, midges and mosquitoes.   Other beneficial flies include Marsh flies (Sciomyzidae) that prey on slugs and snails.Soldier flies (Stratiomyidae) and Robber flies (Asilidae), which prey on flying insects.

 If you are lucky enough to live near a pond or lake, you will have damselflies and dragonflies. These artful fliers belong to the order Odonata - derived from the Greek word for teeth, odonto, referring to the tooth like ridges on their mandibles. Both adults and aquatic nymphs or naiads are predacious. They are invaluable in our wetlands and help to regulate mosquito populations.

Mantids are primarily tropical insects, although there is one native species in British Columbia. The Praying Mantid (Mantis religiosa) was accidentally introduced to New York, in 1899, and a subsequently spread to Ontario. It now periodically shows up in backyard gardens and egg cases can be purchased at nurseries for home pest control.

Although some ants (Formicidea) can be pests in your home, our Ontario species are generally beneficial in the garden. Field ants (Formica spp.),  little black ants (Monomorium spp.) foundation ants (Acanthomyops spp.), cornfield ants (Lasius spp.), Acrobat ants (Crematogastor spp.) and Carpenter ants (Campanotus spp.) are central to ecosystem function. Some of these ants are excellent predators, others are important in mixing and aerating our soil - serving a similar function to earthworms, still others help to decompose decaying matter and breakdown garden refuse, and still others help to pollinate our flowers. Although the tendency of certain species to cultivate aphids and mealy bugs for their honeydew can be problematic, prized specimen's can be protected with a horticultural glue like tanglefoot and washed with mild soap solution.

Parasitic Beneficial Insects

Some beneficial insects are not really predatory but rather parasitic. Parasitoids lay their eggs on or near a particular host species. When those eggs hatch, the immature parasite will eat the host. Parasitoids are often specialists, preferring a particular host. They include thousands of species, including a large group of poorly known parasitic wasps (Hymenoptera) from the super family Chalcidoidea like Trichogrammae, Eulophidae, and the lovely fairyflies Mymaridae. The USDA Chalcid site provides a good description of twenty North American families occurring in this order. The Ichneumonoidea are another super family of  parasitic wasps including Braconidae and  Ichneumonidae. Particular species of these wasps will parasitize particular root maggots, leafminers, sawflies, etc.

Flies (Diptera) can also be parasitic. Bee flies  (Bombyliidae) can be helpful in thwarting cutworms. Tangle Veined Flies (Nemestrinidae) primarily parasitize grasshoppers, Bigheaded Flies (Pipunculidae) are parasites of various species like leafhoppers. Thickheaded Flies (Conopidae) look a bit like wasp and appear to parasitize grasshoppers and unfortunately bees. Flesh Flies (Sarcophagidae) have the rather unseemly but beneficial job of cleaning up animal matter from feces to carion. They also parasitize a variety of insects especially beetles. Last but not least are the Tachinid (Tachinidae) which keep a wide range of plant pests under control, especially caterpillars, beetles, grasshoppers, and sawflies.

Beneficial Arachnids

All spiders (Araneae) are predators. From the orb spinning variety, to crab, flower, wolf, jumping, and ground dwelling types, there are an enormous variety of spiders. Although some have preferences for certain prey, most are generalists. They help to keep insect populations in balance. Although often feared by gardeners, spiders  and the closely related Harvestmen or Daddy longlegs (Opiliones) are important members of a healthy garden community.

 

Beneficial Nematodes

Nematodes are threadlike round worms. There are thousands of species of nematodes feeding on everything from fungi to plants to humans. Although some species are dangerous and others are the bane of gardeners, there are groups of nematodes that are really quite beneficial.  For instance, entomopathogenic nematodes are parasites of insects. They live in a mutualistic relationship with bacteria and together they enter an insect host and feed on that insect. Nematodes exist naturally in healthy soil, preferring moist soil. Some genera may be purchased at nurseries. Nematodes require moisture, so it is important to keep the area inoculated with nematodes well watered.

Earthworms (Good and Bad)

Earthworms (Annalids) are beneficial to gardeners as they increase soil fertility and soil aeration. Unfortunately, the majority of earthworms are not indigenous to North America and have been introduced. Nineteen species of earthworm are found in Ontario, only two of these are native to North America. Unfortunately introduced earthworms have displaced native species and their ability to quickly decompose fallen leaves inhibits the growth of certain plants. They are changing the flora and fauna of the North American Forest. (For more read Non-native invasive earthworms as agents of change in northern temperate forests).

 

These are a tiny fraction of the beneficial insects that pass through your garden each year. Their presence is a sign of health. Help them stay.

May the toads nestle in your garden and keep the slugs at bay.


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