MadSci Network: Zoology

Re: Do poisonous creatures have to be cold-blooded?

Date: Thu Feb 13 06:55:17 2003
Posted By: David Hubble, Consultant/Owner
Area of science: Zoology
ID: 1041266293.Zo

Hi Kieran

Good question! There aren't many examples of venomous warm-blooded animals 
but there are a few (all mammals, no birds);

1. Shrews and moles have toxic paralysing saliva which they use when 
biting to subdue their invertebrate prey such as worms. One mole-nest has 
been found with 1,280 stored worms. They can also deter attackers as an 
American short-tailed shrew stores enough venom to kill 200 mice.

2. Skunks are well known for spraying foul-smelling fluids at attackers, 
but the substance they use (butyl mercaptan) is also poisonous as it 
damages the mucous membranes of the nose and eyes causing great pain. The 
skunk's African relation, the zorilla, also has the same scent glands, but 
much less effective chemicals.

3. Most impressive and relevant to your conversation about Australia is 
the duck-billed platypus (really!) - it has hollow spurs on the ankles of 
its hind legs which are attached to poison glands further up the legs. The 
spurs are usually hidden under folds of skin but can be raised and stick 
into the target by kicking. The venom is quite powerful and will kill a 
dog-sized animal, or cause great pain to a human. It isn't really known 
why they evolved this mechanism but theories include inter-male rivalry, 
or use as defense against predators.

So, most venomous animals are cold-blooded but then again most animals are 
cold-blooded. There are millions of species (most undescribed!) of 
invertebrates but only a few thousand species of birds and mammals. So if 
one in a thousand animals was venomous, there would be the above short 
list of warm-blooded animals, but many thousands of cold-blooded ones 
which is what we see.

As far as I am aware, there are no other examples of venomous warm-blooded 
animals - if there are, they've only recently been discovered! As for your 
other question, 'poisonous' and 'venomous' can be interchangeable up to a 
point but 'venomous' implies that the substance has evolved specifically 
to be used. Therefore a snake, platypus or shrew can be venomous, the 
substances they use are venomous or poisonous, but a jar of drain-cleaner 
or other harmful chemical is just poisonous (or toxic). Similarly, the 
liver of the polar bear is poisonous to eat due to the extraordinarily 
high vitamin level, but it couldn't be described as venomous as it is not 
meant to be used as a poisonous gland. I hope that bit makes sense - and I 
think the rest answers your question.


Dr David Hubble, UK

Steve Mack adds:

I'm not sure if these count as venomnous, but there are at least two
genera of poisonous bird. Both the Pitohui (Pitohui dichrous) and the
Ifrita (Ifrita kowaldi) have high concentrations of homobatrachotoxin
in their skin and feathers. This is the same toxin found in the skin
of certain "poison dart frogs" common to South America. Both birds
live in Papua New Guinea, and it seems likely that the toxin comes
from something that they both eat. I understand (although I don't
have references) that there have been descriptions of other toxic
bird species as well.

Homobatrachotoxin in the genus Pitohui: chemical defense in birds?
Science. 1992 Oct 30;258(5083):799-801.

Batrachotoxin alkaloids from passerine birds: a second toxic bird
genus (Ifrita kowaldi) from New Guinea. Proc Natl Acad Sci U S A.
2000 Nov 21;97(24):12970-5.

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