Be a Better Farmer: Understand
the Living Soil
Part 2 - Good Bug or Bad?
Originally Printed in Country Guide, Spring 2001
Table of Contents
- Introduction
- Wireworm
- Millipedes
- Centipedes
- Symphylans
- Related Links
Introduction
This second installment in our living soil series focuses on 4 soil-dwelling
creatures that often get confused with each other. It is important to
be able to identify them, however, so you know whether to control them
or help them thrive.
Wireworms
The bad actor in this group is the wireworm. A crop pest, it feeds on
seeds, germinating seedlings and roots of corn, soybeans, wheat and edible
beans.
Often confused with millipedes and centipedes, wireworms are the larvae
of click beetles, which you may fine attracted to lit areas around your
house in late July. These adults do not damage crops.
The larvae have long, hard cylindrical bodies that are copper-brown in
colour. True insects, they have only 3 pairs of legs. Click beetles can
have a long life cycle, some remaining as larvae and potentially doing
damage for 3 to 5 years. So if they were there the previous season, they'll
probably still be in your field this year. They prefer reduced or no-till
fields, sandier soils or fields where sod, small grains or alfalfa have
been plowed under.
Wireworm larva.
Seed treatments containing lindane protect germinating seed against this
pest. If populations are high, an in-furrow or banded insecticide may
be needed to protect the growing seedling. No rescue treatment is available.
Millipedes
Millipedes, in contrast, are beneficial. They shred organic matter and
mix it through the soil. This gives smaller soil organisms like fungi
and bacteria greater surface area to work on, and speeds residue breakdown.
Millipedes have hard cylindrical bodies, usually dark brown, gray or
black in colour, and between 30 and 400 pairs of short legs. When disturbed,
they usually curl up. They're easily confused with wireworms and centipedes.
The key here is the number of legs and the body shape.
Absolutely harmless to humans and buildings, they may occasionally feed
on garden plants if a garden is over-watered or has high amounts of plant
debris and rotting material on the surface. But take a walk at dark to
make sure the damage isn't caused by earwigs.
Because millipedes need moist, cool soil with lots of decaying residues,
they respond well to reduced tillage.
Centipedes
Centipedes are also good (but ugly) bugs. These predators feed on pests
such as slugs, symphylans, spiders, flies and cockroaches. Usually yellow
to reddish brown, they're flat-bodied and have one pair of long legs per
body segment. With at least 15 pairs of legs, centipedes are not true
insects. They are rather shy and run very fast when found.
Their favoured habitat is dark, moist, protected areas under leaves,
logs and residue. As with millipedes, farming systems that leave crop
residues on the soil surface and involve a variety of crop rotations will
encourage centipede populations.
Often confused with millipedes, centipedes can be identified by their
flat body shape and leg arrangement. They won't harm humans or buildings.
Centipedes are actually good to have in your house. They hunt less welcome
visitors like cockroaches and spiders.
Symphylans
Fourth on our list come symphylans. These bugs are both good and bad.
Occasional pests of corn, they feed on germinating seed, gouging kernels.
They may also feed on roots and root hairs of corn, alfalfa, carrots,
and potatoes.
On the other hand, they mostly survive by scavenging nutrients from plant
debris. By shredding residue for faster breakdown, they keep plant nutrients
cycling through the soil.
You'll find symphylans in damp, high-organic, sandy soils usually when
crops are germinating slowly from a cool, wet spring. They are small (usually
less than 1.5 cm long), white to brass coloured, and have only 12 pairs
of legs (one pair per segment like centipedes). Their distinctive antennae
are jointed to form a Y shape. They are often confused with wireworms
and centipedes.
It's not known whether symphylans can be controlled with seed- or soil-
applied treatments, but they seldom reach crop-pest levels in Ontario.
A steady supply of crop residues and less soil disturbance (no-till) encourages
these creatures to be good soil citizens.
Since many of the good critters in your soil look like bad guys and vice
versa, it's important to recognize them all.
Related Links
