University of Vermont Extension
Department of Plant and Soil Science
COMMON BENEFICIAL INSECTS
Dr. Leonard Perry, Extension Professor
University of Vermont
Although we focus on the insects
that destroy our landscape plants and crops, these bad insects give a bad name
to virtually all insect species which are actually good. They either do no harm, provide food for
desirable species such as birds, or attack and kill the pests we don’t
want. Here are ten common beneficial
insects we should be aware of in our yards and gardens.
Lady beetles, also known as ladybugs
and ladybird beetles, are perhaps the most well-known beneficial insect. The brightly colored, rounded beetles are
often orange, but can be red, pink or yellow, and with or without spots. Both the larvae (the caterpillar stage before
they turn into adult beetles) and the adults can eat hundreds of aphids in
their lifetimes. They also eat insect
eggs, mites, and soft-bodied insects such as mealybugs.
One of these, known as the Halloween
lady beetle, enters homes in large numbers in the fall. Proper screening, patching cracks, and just
vacuuming them up are simple controls.
Ground beetles range in size from a
quarter inch to over one inch long, and are shiny brown, black, or
bluish-black. They have long legs and
antennae. Most feed at night on caterpillars
such as armyworms, cutworms, and grubs.
They may even eat small snails and slugs.
pair of adult ground beetles can eat over 300 gypsy moth caterpillars per year.
Praying mantids also are known by many,
being up to three inches long, and with its enlarged front legs held out in
front as if praying. They are not
protected by state laws as some believe.
In fact, they may do more harm than good, eating anything they can
including honey bees, other beneficials, and even each other!
Dustywing adults are a quarter inch
long, or less, with gray dusty-colored wings.
Larvae are often mistaken for plant debris. Both stages of this insect feed on spider
mites, aphids, and scale insects. They
are considered one of the most uncommon, unrecognized, and under-appreciated of
the beneficial insects.
Lacewings, both green and brown, are
about three-fourths of an inch long as adults, with lacey wings. They are attracted to lights at night, and
give off an odor when handled. Larvae are like small alligators, with sickle-shaped
mouthparts (mandibles). Green lacewing
larvae are called “aphid lions” from their large consumption of aphids, as well
as mites and other small insects.
Hover flies, also known as syrphid
or flower flies, closely resemble wasps and bees yet they don’t sting. One key difference is that they have only two
wings. Larvae resemble tiny slugs, and
often are found feeding in aphid colonies.
Each larva can eat over 400 aphids.
Attract adults with flowers that provide lots of nectar and pollen.
Predatory bugs feed on nectar and
pollen too. They include several
species. Big-eyed bugs are black and
white with silvery wings and bulging eyes.
They feed on most insects they can catch, including chinch bugs, small
caterpillars, mites, and insect eggs.
Minute pirate bugs are similar, with similar feeding. Damsel bugs are under a half-inch long,
longer than wide, and
long legs. They eat aphids, small caterpillars, leafhoppers, plant bugs, and
stink bugs differ from those that feed on plants, in having a distinct spike on
each shoulder. They feed on over 100
types of insects.
Predatory wasps include ones that
can sting us, and so we usually kill them on sight. Bald-faced hornet, yellow jackets, and paper
wasps though, are important predators of caterpillars and similar soft-bodied
insects. For this reason try and coexist
with them, only destroying nests (using proper precautions) if they threaten
people and pets.
Parasitic wasps are a large group of
many species, most tiny (under an eighth inch long, so often overlooked) to an
inch and a half long. They lay eggs
inside hosts such as aphids and caterpillars. Once the larvae hatch, they
consume the insect hosts. Swollen aphids,
and caterpillars with white eggs on their back, are examples of this beneficial
insect at work.
Parasitic flies, also known as
tachinid flies, are a diverse group of over 1,300 species. They often resemble, so can be mistaken for,
houseflies, bees, and wasps. Many lay
eggs on hosts, the hatching maggots boring into the hosts and killing them
through feeding. Hosts include
caterpillars such as of the gypsy moth, beetles such as the Japanese, sawfly
larvae, true bugs, and grasshoppers among others.
You can find diagrams of these
insects, more information on them, and methods to help and not harm them, in
the online Extension bulletin 7150 from the University of Maine.
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