A problem for insects (but also not exactly fun for pilots)
Insect lovers living in temperate climes have a hard time in winter. The hums and buzzes of flying insects can’t be heard and to even spot an insect in winter is a lucky break. When I was a child my grandfather encouraged me to look for insects on our winter Sunday walks by promising me a candy for every insect I saw. Nowadays that the winters have become a little warmer than 70 years ago, he probably would have needed quite a handful of candies. However, to see insects flying in the cold winter air is still not easy, because flying in winter is a problem for insects as well as airplane pilots, but for different reasons.
On the web I came across the statement “at low temperatures insects are not able to fly”, attributed to Dr Soszynska-Maj. But this is simply not true. Let’s start with the champion winter fliers: winter moths of the genus Operophtera. I had given a PhD-project once to a student from Hong Kong to examine the eyes and retinal organizations of males and females of the winter moth Operophtera brumata. To see someone in mid-winter with a butterfly net must have amused people, but he managed to catch many individuals – all males (for the females are chubby and wingless, waiting on the stems of trees for a male to find them). The males have rather large wings and very slim and very light bodies. Since they do not feed as adults, they do not carry extra weight in their degenerated digestive tract. The amazing fact about these male moths is that they do not shiver to create body heat (like bees or other flying insects do). It’s been reported that their flight muscles work at temperatures close to 0⁰C and they have been seen to fly even at -3⁰C, although with wingbeat frequencies as low as 2 to 4 beats/sec to save energy.
Another group of moths flying in winter are some Cuculiinae, but to warm up their flight muscles they begin to shiver at temperatures as low as -2⁰C. In contrast to the winter moths that my Hong Kong student S.T.F. Lau had worked on, the winter Cuculiinae that the American entomologist Prof. Bernd Heinrich had studied, do replenish their energy reserves by licking up sap from injured trees. Moreover, they possess quite an elaborate circulatory system that ensures that heat from the 35⁰C warm thorax with its flight muscles is not lost to the abdomen with its temperature just above 0⁰C. Countercurrent heat exchangers in the abdomen and the thorax prevent undue heat losses. Unlike Operophtera brumata with its wingless females, the Cuculiinae moths do have winged males and also winged females.
Other species of flying insects at the beginning of or during winter are various species of some rather small crane flies, in particular those belonging to the family Trichoceriade. In these insects the long-legged males sometimes aggregate in swarms and in Norway, according to Sigmund Hågvar and Ewa Krzeminska, for example, they are present throughout the entire winter months with the highest numbers caught in December on windless days and at a temperature of 0⁰C. Loose snow that covers the ground helps these insects to shelter and to survive particularly cold phases. Insects commonly referred to as snow flies (like Chionea spp.) are also crane flies, but they are wingless and clamber around piles of snow. Cold-hardy flying species of insects, however, can be found amongst the stoneflies, of which I could always observe some as early as March and April in northern Finland, usually with ice and snow still around. Their black body coloration contrasted nicely with the whiteness of their environment, but although they were winged, they were usually not inclined to fly away and were just sitting on the surface of the ice that was covering the stream they had emerged from. Frozen individuals that had not left the ice before nightfall could be seen stuck to the ice the next morning. It seemed their blood, just like that of the aforementioned Cuculiinae moths did not contain any anti-freeze chemicals. You may feel chilly searching for insects in winter, but let me tell you, to see a live insect in the cold will certainly warm your heart – if you are an entomologist.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
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