Stages in a grub's life
Comparing different grub species'
Identifying individual grubs
Above: Grub. Beetles lay eggs which become
these soil-dwelling larvae.
The grubs that are lawn pests eat grass roots.
Below: Pupa: As it reaches maturity the grub
pupates. It emerges from its pupa case as a beetle.
Left: While pupating, our adversary is a
For most lawn-dwelling grubs,
this stage comes in spring. Since it
doesn't eat and is protected by a relatively hard
shell during this stage, stomach poisons and
biological agents are not effective.
Month by month with four kinds
of lawn pest grub
Below is a comparison of the life cycles of some of the most
commonly seen lawn grubs.
Several important things to
notice about these life cycles
Each grub species follows its own schedule. For instance, native
North American June beetles require three years to mature. (We do
see the species every year when a batch finishes its underground
stint and emerges in late May or early June.) In contrast, Japanese
beetles mature in just one year, emerging several weeks later than
Since single-year species such as Japanese beetle and European
chafer go from egg to adult three times as fast as a June beetle,
each does as much damage in one year as a native June beetle does
in three. Japanese beetles and European chafers also tend to
occur in much larger numbers than the native June beetles, so they
have the potential to do far more damage.
These grubs feed, rest, mature and
emerge at varying times but they have in common a late summer
period (chart detail, right) when the grubs are young and
feeding. That's when most are vulnerable to pesticides and
biological control agents such as predatory nematodes.
There is also a convergence of resting/pupating stages in
spring, making that time the least effective time to apply grub
killers. (So why are these products marketed so vigorously in
spring? Because that's when homeowners are focused on lawn care and
willing to spend money.)
Identifying individual grubs
It's helpful to be able to distinguish between grubs and
non-grubs, and between grubs of different species. One very
important reason to make the effort is to maintain awareness that
there are good
and bad beetles as well as many other small creatures living
below ground. The majority of them are important to soil condition
and fertility and so we should not be trying to kill them.
When we can identify a grub as a pest, then we can determine its
life cycle and fine tune any control measures.
Grub vs. cutworm
Cutworms are not grubs. Cutworms are rubbery, elusive
caterpillars -- moth larvae of various species. There are several
especially pesty types such as the black cutworm. They hide out in loose soil by
day and move up at night to wrap around and chew on small stems.
Since their chewing usually kills the foliage on that stem a heavy
population of them can do some serious damage to starter annuals
Right, above: Cutworm moth caterpillar
Right, below: Chafer beetle grub
Leg number and position is probably the most
certain telltale between grubs and cutworms:
Grubs -- beetle larvae -- have 3 pairs of legs,
all attached to the body segment right behind the head, a segment
called the thorax.
Cutworms -- moth larvae -- appear to have more
than 3 sets of legs. In addition to six true legs attached to their
thorax they have two or more pairs of "prolegs" attached to the
One grub from another
Sometimes we need to know which beetle grub species we're
dealing with, at least to narrow it down between troublemaking
species and those that are beneficial or benign.
The surest method is to keep suspect grubs in captivity until they
emerge as adults.
If you can't do that, look at the grubs' butt ends -- their
Most grubs are on their way to distinctive looking adult
beetles. However, to identify them in their grub state, examine the
butt end. What you look for is type and arrangement of hairs,
pattern formed by the anal slit and other marks. For the most part,
what you have to work with will be descriptions of pest lawn grubs,
the object of most turf tenders' interest.
Above, left: common pest grub rasters. Ugh. Ugly but necessary
nitty gritty about grubs.
How good are you at beetle grub I.D.? Look at our sketches
of the butt ends of the most common lawn pest grubs, and then at
this photo of a chafer's raster.
To learn more about what you've read in this
Destructive Turfgrass Insects: Biology, Diagnosis and
Control, by Daniel A. Potter
Lawn Care: A Handbook for Professionals, by Henry F.
Decker, Jane F. Decker