Hi beetlers, apologies for the lapse in blogging, but unless you hadn’t noticed, it’s been snowing - a lot, and here in good old Blighty, we are not very good at dealing with snow.
Inevitably this poses the question, or at least, people are always asking me this question (usually at parties – yes, I know, what fun!) what happens to insects when it snows / freezes? Oh yea of little faith, I say, don’t you think that these super-organisms that have been around since the early Carboniferous period (c.350 million years ago) would have evolved to survive all manner of hostile environments and even extinction events without being able to cope with a bit of snow?
They look at me blank eyed, and naturally I am compelled to elaborate…(the moral of this tale is not to corner an entomologist at a party, you are far better off nabbing an accountant or lawyer…)
Anyway, many would think that insects, (let’s be beetle specific) die off in the winter, and this in some cases is true, but, something must survive, whether it be egg, larva or adult.
There are a number of strategies available to the beetle.
The unremarkable looking Bolitophagus reticulatus (Family: Tenebrionidae) is freeze tolerant and freeze avoiding.
Though beetles are winged and many capable of strong flight, they are not prone to migrate (at least not deliberately). Some well know migratory beetles are the pollen beetles (Family Nitidulidae) and the ladybirds (Family Coccinellidae). But they are migrating from their overwintering site to their spring and summer breeding and feeding grounds. The pollen beetles and ladybirds overwinter as adults, where they seek warmer environments and live like hippies in communes. Ladybirds are famous for it, moving in with us humans to take advantage of our central heating (though central heating can kill them off by raising their metabolic rate too high to live without food).
Many beetles overwinter, which means whether it be egg, larva or adult, they will have developed a survival strategy for the winter. There are a few ways they can achieve this, depending on the species, some will go into diapause, some will produce antifreeze, and some will remain active throughout the winter (this is true of the aquatic insects where they remain active in the larval stage in fast flowing rivers and streams that do not freeze).
Insects including beetles are ectothermic which means they get their heat from external sources. Most insects cannot survive temperatures below 4°c and so have developed life-strategies to survive the winter.
Diapause is a ‘pause’ in the usual cyclical activity of an insect. This usually coincides with seasonal weather conditions, where an insect is programmed to go into a temporary state of inactivity, to combat lack of available food, and temperatures too cold to ordinarily survive. Such factors as day length and temperature are triggers to ending diapause over the winter period.
Dendroides canadensis (Family: Pyrochroidae) enjoys diapause.
Insects which inhabit higher altitudes employ a state of suspended animation, which means they can literally freeze, but as temperatures rise begin to thaw and go about their business.
Overwintering strategies are divided into freeze avoidance and freeze tolerance, and these can differ between the northern hemisphere and southern hemisphere. Freeze avoidance (by keeping the body fluids in a perpetual liquid state) is usually found in insects in the northern hemisphere where weather conditions are more predictable and colder. In the southern hemisphere freeze tolerance is more common due to the changeable weather conditions; though generally milder the insect requires the ability to produce antifreeze in reaction to sudden cold snaps. Freeze tolerance means the beetle can avoid the internal freezing of its bodily fluids by producing antifreeze – yes, that’s right antifreeze! Not quite the toxic looking blue liquid we put in our cars in winter, rather a naturally derived fluid made from Glycerol and Glucose (essentially sugars and alcohols). These allow the bodily fluids to drop to below freezing temperatures without causing damage to the body cells and tissues.
The Hermit Flower beetle, Osmoderma eremicola (Family: Scarabaeidae) larvae are freeze tolerant.
How does it work?
When temperatures reach freezing point, ice crystals form, but they need nuclei (such as dust or bacteria) to form around. The elimination of waste fluids from the body reduces the number of nuclei available for ice crystal formation, this, along with the production of antifreeze ensures that the insect will not freeze. Antifreeze proteins lower the temperature of freezing in the insects body (this is called ‘supercooling’) and so the body fluids cool below freezing point in a liquid rather than a solid state. Supercooling will take body temperatures down as far as -42°c.
Cucujus clavipes puniceus (Family: Cucujidae) is 'supercool'.
All specimens images from the Museum's collection (taken badly with an iphone!)