Are flies sometimes cold?

Answer

Dear Helen,

insects and therefore flies can indeed be cold, not as we experience it because their nervous system is rather limited; but they will at least make an effort to avoid the cold, just like extreme heat for that matter.

When it is cold they look for a place in the sun, when it is warm a place in the shade. So they can register cold and heat. This is important for insects, because they are cold-blooded and therefore cannot produce body heat themselves, which means that they take on the temperature of the environment.

When insects are cold they are rather sluggish; to become active, the body temperature has to rise. Many winged insects can raise their body temperature by, for example, vibrating their wings; others will sit in the sun to “sunbathe” and let their temperature rise before flying away.

If the ambient temperature starts to drop in the autumn/winter, the insects can respond in different ways. Some die before the winter, but have already provided offspring before, eg by laying winter eggs. Others will migrate to warmer regions, away from the colder temperatures.

Still others remain in place, but will go into diapause, a kind of resting state where metabolism is lowered so that less energy is used. Often these insects survive by producing a type of natural “antifreeze” that prevents the formation of ice crystals in the body.

Still others flee the colder temperatures by looking for a sheltered place to hibernate such as deep in the ground (eg grubs) or in dwellings (eg lacewings and ladybugs).

Kind regards,

Hans