5
Mosquitoes are most active in
the early morning and late
evening, in low vegetation, while
purple martins feed during the
day, high in the sky. Having purple
martins on your property offers
many other rewards, but don’t
count on them to control
mosquitoes.
The situation is similar when it
comes to bats. Depending on
where you live, and the species
that inhabit the area, bats may
eat a significant number of
mosquitoes, but their primary diet
is moths and beetles.
The little brown bat seems to
be the most voracious consumer
of mosquitoes, especially in
urban areas, so it can be
worthwhile to install bat houses
and try to attract them. As with
purple martins, bats provide
many other benefits, so
providing suitable habitat for
them is definitely worthwhile for
reasons other than the control
of West Nile Virus.
Mosquitoes can only reproduce
when there is water available, but
getting rid of birdbaths and ponds
on your property is not a good
step to take. All wildlife needs
water, and it is becoming more
and more limited, whether due to
development, the filling in of
wetlands, or drought conditions.
As long as proper precautions
are followed, providing water
sources will encourage wildlife,
including mosquito predators,
without raising the risk of
contracting West Nile Virus.
While standing water can harbor
mosquito larvae, the water that is
preferred by birds and other
wildlife is changed and freshened
frequently, and, even better, may
be kept in motion with a drip or
small fountain system. Moving
water does not attract
mosquitoes. Standard bird baths
should be filled with fresh water
every one to two days.
Larger bodies of water such as
ponds, even if they don’t include a
waterfall or other source of
movement, will encourage the
presence of frogs and other
creatures which happily eat
mosquito eggs and larvae, as will
any fish that you include.
Female mosquitoes look for
sheltered spots to lay their eggs,
so don’t create “trapped" water,
such as between rocks, in gravel,
or in very shallow (less than 6")
areas.
Avoid plants with leaves that
hang over the edges of the pond,
since they will provide protection
from predators. The tops of
potted plants can provide
suitable egg-laying areas if they
extend out of the water, so keep
them submerged.
Pond sides should be steep,
and provision should be made for
future draining of the water if
needed. If you incorporate a
waterfall, avoid designing it with
small pools that will hold calm
water.
Fish are wonderful mosquito
predators, so allow sufficient
depth in your pond to stock it.
Remove excessive organic
material, such as leaves or
flowers, since it can decay and kill
off the fish.
Don’t overfeed your fish, and
thin aquatic plants enough to
allow the fish to swim easily
throughout the pond. Be aware
that frog eggs are also tasty
fish food, so if you want to
encourage amphibians to multiply
you will need to have a section of
your pond inaccessible to the
fish.
Visual inspection will allow you
to detect mosquito larvae in the
water. This will be easier if you
collect a sample in a white
container, which makes the larvae
show up better. They will swim in
a wiggling, sideways manner.
Pupae are rounder and have a
rolling motion.
If you determine that you do
have a mosquito presence, in
addition to following all of the
above practices, you might want
to add a “mosquito dunk," which
is a commonly-available donut-
shaped concentration of Bti
(Bacillus thruingiensis
israelensis). It will kill mosquito
larvae (but not eggs or pupae)
without harming birds or fish or
other wildlife. These are also
appropriate for birdbaths which
don’t have moving water.
If reading all of the above
precautions still leaves you
nervous, it is important to
remember that humans are not
very good hosts for West Nile
Virus, and that only a small
percentage of people will
become ill even if they happen
to get bitten by an infected
mosquito.
The toll is greater on wildlife,
but it is thought that, as in
countries where WNV has been
common for many years, most
species will develop a resistance
to it through the process of
natural selection.
In the meantime, as we deal
with its spread in this country,
the answer to the problem isn’t
to spray indiscriminately, or to
use chemicals that can put us
at potentially greater risk and
harm wildlife and the
environment.
The best thing that we can
do is replace or enhance wildlife
habitat to keep it healthy, and
encourage populations of
mosquito predators.
As you build ponds to attract
dragonflies and frogs, plant
native shrubs to feed birds, and
curb your use of pesticides so
that predatory insects can
thrive, you will not only be helping
wildlife, but you will be protecting
yourself and your family.
