Overwintering Larvae

Quite a few of our butterfly larvae spend winter in diapause and complete their cycle the following spring. The feat is quite complex and achieved in a couple of different ways. They are the same principles used by various other life forms that confront winter head on. If most insects were simply deprived of migration they would succumb to the elements long before the first snow fell. Without a mechanism in place, after thawing out in the spring, most would suffer from total cellular breakdown brought about by expansion....the result of freezing. Cells would be torn apart and life would not return. In order for the transition to be successful these larvae have developed the ability to produce body chemistry changes that allow, at most, only partial freezing thus protecting the vital body parts from breaking down. So how do they do it? The explanation offered here is a brief synopsis of an obviously complex strategy and offered only as a first step toward a complete understanding.

One way this is achieved is by manipulating the cell's natural salinity by allowing partial dehydration of their tissue. This effectively increases the salinity level of the cells which in turn lowers the temperature at which the larva will freeze........to a level not likely to be encountered. This is bolstered by the actually formation of ice crystals in the blood of the outer layers of cells. By the formation of these ice crystals addition moisture is essentially removed which in turn further increases the salt ratios of the vital internal cells. The larva gives the impression of being frozen solid when in fact only the exterior is frozen leaving the vital cells protected. An unusual approach but very effective.

Another strategic way is that some larvae have acquired the ability to produce glycerol. This acts as an antifreeze agent. This in combination with natural salts, already present, keep the larvae freezing point well below what it will face in normal circumstances. This is a slightly different twist and would appear to be every bit as effective.

No doubt conditions faced in severe winters will override either of these approaches.......in the long run they are extremely successful.

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