When we set out to kill grubs:
Beneficial insects are victims
All the grubs in an area come under fire when we target grubs,
no matter what tactic we use. Even the good-guy beetle species suffer. Probably
hundreds of beetle species dwell in the average, healthy North
American garden and the great majority of these are beneficial or
benign.
Other ground-dwelling predators of insects, slugs and snails are
at risk when insecticides enter the soil. For instance:
- Have you seen a firefly? You probably didn't realize that many
glowworms and fireflies (161 North American species) live in the
soil as youngsters, where they are voracious insect eaters...
unless they are killed off by pesticides in the soil.
- Earwigs, too, are soil-dwellers that hunt slugs and other
undesirables.
Pests may increase
Harmful insects of many kinds can get out of hand when good-guy
beetles, glowworms, firefly larvae and others are not around to
hunt them.
- One ladybug or ladybug larva removed from the picture can mean
a lot more aphids, scale, corn borers or the like will live to
breed and multiply -- since a ladybug can eat 30 to 60 of those
pests per day.
- Consider earwigs, again. Many people know earwigs after
suffering an infestation of pesty, non-native earwig species. In a
pesticide free, balanced environment such infestations are rare,
while beneficial earwig species are present and active but
low-key.
- Some pests survive pesticide application and pass on
resistance. Conditions or the pest's position or stage of growth
may result in a sub-lethal dosage or the pest may have inherited
resistance from a survivor in a previous generation. Numerous
chemicals have become ineffective in this way, especially when used
continually. That's one reason pest management strategies developed
through university research teach us to apply pesticides only when
pest numbers are actually high enough to cause trouble.
Soil condition is degraded
So much of what makes a soil
"good" is the life in it. We should think twice before trying
to reduce a soil animal population.
When grub killers put a dent in the soil animal population (not
only grubs but critters such as underground insects and worms):
- Natural aeration slows or stops. Water does not penetrate well.
Lawn roots and other roots struggle or die in dry, airless
soil.
- Fertility declines, as fewer decomposers are there to release
nutrients.
Larger animals that eat insects are affected
Birds are often victims of grub killer when it contaminates the
insects they eat. Grubs are important bird food -- nutritious,
easy-pickins for a robin. Even seed- and fruit-eating birds switch
to collecting insects during nesting season in order to provide
higher protein to their young. Nestlings die when adult birds bring
them pesticide-laden grubs.
Scientists are registering connections
between neonicotinoids (such as imidacloprid, one of the most
widely-used soil-applied pesticides) and declines in
frogs, toads, bats and other helpful animals.
Human lives are also affected by grub killer.
- The effects touch not only those who apply the chemical or live
in that garden but those who handle it all along the way from
factory to garden center to gardener.
- The most risk of acute symptoms come to those who handle the
chemical in concentrated form, as in the package prior to spreading
or dilution. The warnings are there on the package label.
- Chronic exposure, synergy (combinations of chemicals) and local
accumulation in soil and water occur, too. Some of these risks are
known, others are suspected.