FROZEN MAGGOTS AND OTHER INSECT SURVIVAL STRATEGIES
Today we continue our annual look at what makes this season special, a time when nature is doing much more than just going to sleep for three months. Welcome to the Science of Winter.
More than a century ago, someone figured out there’s a way to make some insects sit very still. This helps if you are a nature photographer and you want to pose them.
You make them cold first, then get your camera. This doesn’t even kill the bug, but rather puts it in a temporary state called “chill-coma” where it can’t move its muscles until it warms up.
At Western University, Brent Sinclair and his PHD student, Heath Macmillan, learned some years ago that they could use chill-coma as a way to measure the cold tolerance of insects.
They also tracked the chemical changes that happen inside the insect.
They found crickets lose the ability to maintain proper water balance in the cold so when they are chilled, water and sodium move from the insect’s blood, called hemolymph, into their gut. The resulting chemical imbalance in their blood, with too much potassium, leaves muscles unable to function.
Macmillan is now at Carleton University while Sinclair is still studying how tiny insects survive a Canadian winter without freezing solid, or in some cases, in spite of freezing solid. Insects don’t create body heat as we do, but they have a lot of very different strategies.
“There are a bunch of things that just migrate. Monarch butterflies fly to Mexico for the winter,” Sinclair said in an interview.
“There are thing that migrate by just digging down. A lot of moths that are active in the summer, they spend the winter 30 to 50 centimetres down in the soil.” (They do this as juveniles of the next generation. The summer moths are dead.)
For insects left out in the cold, there are two solutions.
“One is by making sure that they don’t freeze, and the other is to survive freezing and withstand it somehow.”
The emerald ash borer avoids freezing, unfortunately. They build up chemicals that resist freezing such as glycerol — a thick liquid that is easy to make and is similar to what is in a car radiator. There are also antifreeze proteins in some insect species, which bind to ice crystals and stop them from growing inside an insect (or fish, or even plants). Some build up concentrations of sugar or sugar alcohols.
“The other way to keep yourself unfrozen is just not to have any water that can freeze. There are a few species that dehydrate a lot and avoid freezing,” Sinclair said. These are uncommon and are mostly in the High Arctic.
Many insects lay eggs in the summer or fall, and it is only the egg that overwinters. Small, waterproof eggs can have high concentrations of protective chemicals in them.
A further insect strategy is to survive despite being frozen solid, with Sinclair noting: “A lot of these guys do this.”
For instance, there’s the popular woolly bear caterpillar, and the goldenrod gall fly. (This is a fly that lays eggs inside the stem of common goldenrod. The growing young maggot makes a lump in the stalk, or gall.)
“Ice starts forming, and some large proportion of their body water is converted into ice,” he said. “They’re hard. With a frozen Eurosta (the goldenrod fly), you can drop it and it will bounce.”
His lab is trying to learn how the insect recovers from this.
As a side note, Sinclair said the ash borer is no longer a pest in London (though for all the wrong reasons.)
“They’re history in London now. We have no ash left, or at least none thicker than your wrist,” he said.
The borer needs a mature ash, so it, too, has died off locally. But it would likely return if a new generation of ash trees mature.