Where do all the Insects go in
We are often asked where all the insects go after harvest and whether
a cold winter will lead to fewer pests next year. Like most answers to
broad questions involving insects, we have to first mention that insects
are a huge group of animals - the most diverse in terms of species on
the planet. With so many kinds of insects, there are bound to be many
ways to avoid the problems of winter. Insects have adapted strategies
to survive some very harsh environmental conditions. Basic survival techniques
- Choose to live in the tropics. One way to beat winter is to
completely avoid it. In fact, the majority of insects never experience
cold weather because they do not live in our part of the world at all!
- Leave the country. Much like the fabled "snow birds"
- retirees who flee from Canada each winter - there are some kinds of
insects that migrate. The most notable are monarch butterflies, giant
swallowtails and a few other species of butterflies that perform remarkably
long journeys to avoid hockey season. Most interestingly, it is the
offspring of these southern fliers that eventually make their way back
north in the following year.
- "Hibernate". This is the strategy employed by most
of our northern species to avoid winter. However, "hibernation"
is really a concept that describes mammal wintering. Insects that go
dormant in winter enter a state called "diapause". Their bodies
respond to changes in daylength, temperature, food quality and other
environmental cues. We've had so many issues with multi-coloured Asian
ladybird beetles in the last few years that we know you're all aware
these insects overwinter as adults en masse. Many people are also familiar
with cluster flies which can wander into the house at any time in the
winter. These insects have winkled their way into the house in the fall
and follow the source of warmth from within. Barring the availability
of a structure, they would have congregated in a cave, crack in a cliff,
hollow tree, or other protected place until spring. Some butterflies
even overwinter as adults; a frequently "first seen" butterfly
in spring is the mourning cloak. Leek moth, a pest of Allium species,
overwinters as an adult. And so do some species of mosquitoes (maybe
in your basement right now).
- Pick the least vulnerable life stage. Depending on the species
and which growth stage is best suited to surviving the cold, insects
(and let's not forget mites) will overwinter as eggs, larvae or nymphs,
pupae, or adults. Insects that overwinter as eggs are common and can
be found in a wide range of locations including under tree bark, in
turf, underground, or in other sheltered places. Many overwintering
caterpillars spin a lovely silken cocoon to reduce the chances of freezing.
- Tough it out. Numerous special physiological adaptations take
place in insects to allow them to survive freezing temperatures. Basic
physical processes are slowed by the cold but some insects have remarkable
adaptations to survive actually freezing. Freezing usually disrupts
cell functions and may cause cells to burst as water expands when frozen.
Some insects can replace the water molecules in their cells and cell
contents with glycerol, which acts as an anti-freeze. Others effectively
squeeze water from their living cells to lower the freezing point. These
processes become extremely important for highly exposed insects and
- Slow down and relax. Below the ice of ponds, lakes and streams
in winter is a huge aquatic world where many insects go about their
normal business at a slightly more relaxed, cold-induced slow pace.
Many of our peskiest insect friends such as blackflies and mosquitoes
are aquatic in the larval stage. But then so are some important beneficial
insects like dragonflies.
- Stick close to warm friends. Many youth today want to spend
all of their time in the protective environment of "The Mall."
Insects figured this strategy for easy living out many millions of years
ago - both ectoparasites (parasites outside of the host) and endoparasites
(parasites inside the host) avoid winter by staying on (or in) their
protective hosts. As long as the hosts survives the cruel winter, the
parasites will as well. Bees huddle together for warmth; the colder
it gets, the tighter the cluster.
- Get out and enjoy it. There are a few kinds of insects that
you may see around in the winter. Keep your eyes open on cool days when
you're outside and you may see "snow fleas" (spring tails
or collembola) - small jumping insects - on the surface of the snow.
You may also see winter crane flies and some moths flying even at 0
- Stay under a warm blanket. There are lots of warm places to
hide: hidden in the soil, plant debris, crevices in bark, under blankets
of snow and other protected locations. One of the most productive areas
for winter insect activity is right under a thick warm blanket of snow.
At ground level under a decent depth of snow, the temperature won't
vary much from freezing. Many ground beetles and other insects are still
active below the snow, even if they are a little slower than normal.
Location of overwintering does make a big difference - the more sheltered,
the better chance of survival.
Each type of insect has its own particular strategy to avoid the worst
of winter. For organisms that generally can't regulate their body heat,
winter can be a dangerous time. The incredible adaptations to avoid this
danger exhibited by Class Insecta are truly remarkable.
But to answer the question of whether a cold winter will lower insect
numbers - well, yes and no. To species that have specialized physiological
or behavioural adaptations to handle winter temperatures, the cold means
very little. Instability - fluctuations of freezing and thawing similar
to what we've had the last few weeks - can be problematic to overwintering
insects. For some insects, if their overwintering sites get too cold (e.g.
if there is little snow cover and very cold temperatures), they may have
higher mortality but won't be eradicated by the cold by any means. They
usually catch up in numbers later in the summer anyway.
But in the end, let's put it this way: Have you ever known a summer without
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