Re: Insects at K/T boundary

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Date
Curt Klug wrote:

>     When it comes to entomology, I'm about as dumb as a dung beetle so I
>can't add materially to this interesting discussion.  About all I can do
>is ask a question.  Are there any living insects that can respond by
>hibernation to a nearly instantaneous and prolonged nonseasonal drop in
>temperature such as proposed in the impact scenario?

I'm not an entomologist, but I am a zoologist. So a few general points:

(1) Only a minority of temperate insects can hibernate. Most that
overwinter do so by delayed maturation - i.e, by remaining dormant (or
quiet, anyway) as larvae or pupae in sheletered habitats. Such as being
underground, in rotting wood, trees, underwater, etc. They life cycles are
such that the eggs are laid, and the larvae hatched at *just* the right
time to pass through winter. Relatively few adults can hibernate as such
(e.g., ladybirds, some social insects). So if a sudden cold snap hit
mid-summer England, terrestrial insects would be as badly hit as everything
else.

(2) Hibernation is not always available to animals. Mammals that can do so
must lay down reserves, built nests, etc. Sticking a hedgehog or a bat in a
refrigerator for three to six months will kill it. Mammals can only
hibernate at wintertime when they have been prepared for it, and even then
they have appreciable mortality as many are not prepared.

(3) Birds can't hibernate (as a rule). A sudden cold snap won't cause non
migratory birds to head south. Animals don't know instinctively that it is
warmer near the equator. They either exhibit migratory behaviour - at
certain times of the year - or they don't. Ditto for large mammals like
caribou which migrate. Migration isn't a response like blinking in bright
light, but a geneticly controlled pattern that occurs at certain times.

Conclusion - just because some Late Cretaceous animals might have been able
to hibernate during the (relativey brief and mild?) winters, doesn't mean
they were likely to fare any better than non-hibernating ones.

In fact, the reverse might be true - reptile, amphibians and fish respond
directly to cold temperatures by slowing down and ultimately becoming
torpid. A rapidly cooled fish or lizard will become lethargic, and
certainly over days or weeks become prone to disease, predation etc. Ask
anyone who has kept a tropical fish in a coldwater tank. Do the same to a
mammal or bird which is not in "winter mode" already and its metabolism
will bring about rapid use of energy reserves and eventually death if food
cannot be replaced. For a small mammal or bird, we're talking hours or days
at most. A fish or lizard can go without food for weeks or months.

All the best,

Neale.

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>From  Neale Monks' Macintosh PowerBook, at...

Department of Palaeontology, Natural History Museum, London, SW7 5BD
Internet: N.Monks@nhm.ac.uk, Telephone: 0171-938-9007
Telephone (international): 0044 171 938 9345

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