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By Root 1278 0

blood glucose concentrations are normally precisely regulated by two hormones, insulin and glucagon. When we don’t have enough glucose in the blood we become unconscious, and when we have too much we suffer numerous short-and long-term consequences. We normally regulate our blood glucose at near 90 micrograms per 100 milliliters of blood, although during stress these levels rise slightly. When levels of blood glucose reach and are chronically maintained near 200–300 mg/ml blood, we’re diagnosed as ill with a disease called diabetes mellitus. Diabetes can now be treated by administering artificial insulin, the hormone that the pancreas is not producing in sufficient amounts in one version of the disease. (In Type I diabetes the pancreas is destroyed in an autoimmune response. In Type II there are no or few hormone receptors.)

In frogs that have felt ice crystals forming on as little as a toe, the massive blood glucose levels (to 4, 500 mg/ml of blood that are released in a seeming hyper-alarm response), would be high enough to send us into a coma and death several times over. But to the frogs, which survive it, in part because they are then at near 0°C, and metabolically relatively inert, it is their ticket to survival, to tolerate freezing.

Soon after the frog’s heart and breathing stop, its tissues would become starved of oxygen if metabolism continued. However, at high concentrations the glucose acts as antifreeze, a mechanical protectant from ice crystals, and an agent to help draw water from the cells. It also reduces the frog’s already very low aerobic metabolism and thus acts as a metabolic depressant to conserve the cells’ limited energy reserves for the winter. The glucose that enters the cells also becomes a substrate for anaerobic metabolism when the body can no longer supply oxygen.

Frozen bodies that can revive upon thawing out have long been a pipe dream of cryobiologists. The frogs that hibernate in the forest floor do it routinely, coming out of their frozen state at the first flush of spring when it is time to mate. They, like the hibernating bears I’ll discuss later, are biological marvels that challenge the limits of our beliefs of what seems possible.

14

INSECTS: FROM THE DIVERSITY TO THE LIMITS

It seems astounding to us that some frogs can survive months being frozen, or that a bird as small as a kinglet can stay warm and survive even one winter night, much less a whole northern winter. But why, really, are we surprised? I think it’s because we compare them to ourselves. We feel uncomfortable when we chill only a degree or so and we can’t imagine how a tiny bird keeps warm in a blizzard. Yet for every kinglet that we find in the winter woods hundreds of thousands of invertebrate animals exponentially tinier than a kinglet survive by doing what for us seems unimaginable. Even when we do know what they accomplish we still tend to withhold respect. Why? It’s because most of them are insects. They are animals so different from us that it’s as if they were from an alien world; we find it difficult to identify with their problems. Yet they face the same problems of cold, freezing, and energy balance that we or a kinglet deal with. They have evolved some of the same, and also different solutions, but with different constraints.

To an entomologist and anyone who aspires to be one, there are no life-forms on earth as diverse, varied, tough, and inventive as the insects. In their teeming millions of species, they own the world. We may not like many of them that compete with us for food, fiber, timber, or that suck our blood and spread our diseases, but we are obliged to acknolwedge their tenacious success, and we may admire many of them for their stunning beauty. Within the animal world they have collectively pushed the limits of things possible, in terms of diversity, beauty, noxiousness, social organization, architecture, powers of flight, sensory capabilities, and ability to survive extremes of climate. And when I contemplate these organisms that are much more ancient than us, and that will long