IS CAUDAL LURING A HAZARD FOR YOUNG DEATH ADDERS?
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Originally published in Monitor – Journal of The
Victorian Herpetological Society 16(1)(June 2007):21-22.
Adders (Genus Acanthophis) are unique
among the family Elapidae in that their appearance and biological habits have
evolved in a manner convergent with viperid snakes.
15 recognised species have a relatively stout body, ambush predation and use of
a caudal lure (Hoser 1995).
Death Adders this takes the form of a modified scale at the end of the tail
terminating in a spine. The latter part
of the tail is often of a different colour to the rest of the snake, including
being sometimes white, cream, or black (see Hoser 1989 for photographs of
use of a caudal lure in Death Adders is well-known and has been repeatedly
documented in the literature (including for example Carpenter, Murphy and Carpenter, 1978, Chiszar, Boyer, Lee, Murphy, and
of captive Death Adders over a 30 year period to end 2006 has indicated that
small and neonate Death Adders (Genus Acanthophis)
do not use their tail as a caudal lure to anywhere near the same extent as
large, heavier adults.
the bulk of my observations have been primarily with the species A. antarcticus, I have observed a
similar trend in individuals of all described species from Australia (as per
Hoser 2002) as well as in some from outside Australia.
here are long-term captives and snakes raised from birth to adult.
way of example, none of three newborn female death adders (A. antarcticus) born on 4 February 2002 were seen using their tails
as lures until August 2002. Even then
the observation in one the snakes was unusual in that luring was not repeated
in that snake commonly and it was some months before others also regularly used
their tails as caudal lures.
early 2003 when the three snakes were nearly 50 cm in length, caudal luring
became fairly routine and became even more pronounced as the snakes approached
70 cm in mid 2003. (The snakes were
growing at about 5 cm a month).
of July 2003, two neonate Death Adders (A.
antarcticus) and four neonate Top-end Death Adders (A. cummingi) (two died in June from a virus since identified via
electron microscopy as a reovirus), all born in February 2003 had not yet been
seen using their tail as a lure.
(1972) and others have noted young or neonate Death Adders using their tail as
a lure when hungry.
these printed claims, my own observations indicate that while neonate Death
Adders will sometimes twitch and wriggle their tail as a lure to attract food
when hungry, this is relatively uncommon and remains so for some time after
also been observed by myself that while Death Adders of all ages will sit in a
characteristic position of tail near head, this situation is far more commonly
adhered to in adults than young specimens.
adult not seen in this position can as a trend be deduced not to be
hungry. By contrast, neonates not in
this position may be.
this, caudal luring becomes common as Death Adders approach maturity (at around
60 cm total length).
the captive situation, Death Adders soon learn that the keeper is the source of
their food and will increase caudal luring in response to the keeper looking in
the cage, moving their hand over the cage, moving the cage itself or similar.
fact adults will frantically twitch and wriggle their tails in anticipation of
food, while this is relatively rare in young snakes.
question is; why the difference between the ages?
other facts of relevance follow:
is also noted that in the wild and sometimes in captivity, Death Adders have an
ontogenetic shift in dietary preferences.
young Death Adders have a strong preference for lizards, shifting towards a
preference for rodents and birds as they age.
This is masked somewhat in captivity as most snakes eat what the keeper
feeds them (even if this is by force or assist feeding).
the trend towards warm-blooded food in wild specimens is evident from my own
inspections of road-killed Death Adders in various parts of Australia.
is also a reflection of food availability in terms of the size of the Death
notable aspect of Death Adder behavior gained from wild specimens is seen in
the activity patterns.
females are sedentary and rarely move. Adult males are likewise, but are more
commonly seen active at night.
presumed difference is because the males are looking for mates.
terms of Sydney Death Adders, this has been confirmed by myself in the 1970's
and 1980's on the basis of the following:
Wild male Death Adders
are active and move about in tandem with their counterparts in captivity. The movement is often in response to weather
conditions and time of year, noting that temperature cycles in captivity ran
more-or-less in tandem with those in the wild.
These wild snakes when
brought into captivity have no interest in food, but will immediately mount and
mate with any available females. Hence
feeding being ruled out as a reason for the movement.
The same mating activity
is seen in captive adult males that become unusually mobile.
In other words, and with
rare exceptions, the only activity commonly seen in adult Death Adders in the
wild stems from mating activity and not active foraging for food.
to this, young immature Death Adders are commonly seen active at night. While the sex ratio of adults found crossing
roads at night is heavily weighted in favor of males, further corroborating the
assertions of fact above, the sex ratio of immature snakes is 50:50.
mating cannot be a consideration for these snakes the only remaining
consideration can be that movement is due to a search for food.
hypothesis, in part goes against what's known about Death Adders being ambush
also know that thermoregulation is not at issue as the snakes are active at
night, meaning that the wide-ranging activity observed is not immediately a
result of a need to find warmer or cooler sites and that the general
environmental temperature at ground level tends to be fairly even.
the increased foraging by young Death Adders indicate that these snakes are not
always ambush predators? Does it indicate that they may also actively stalk and
capture their prey?
opinion is yes.
is also reflected in younger captive Death Adders which will when hungry be
seen actively moving about their cages.
adults by contrast rarely do.
the above indicates that the lack of observation of caudal luring in smaller
Death Adders is not something anomalous in terms of my observations or the
captive situation, but rather an actual appraisal of the reality in both
captivity and the wild.
this to be so, it becomes clear that there must have been some selective
pressure forcing Death Adders to tend to curtail caudal luring when young and
increase it as they gain size and weight.
question then becomes what is this pressure?
guess is that a small neonate snake using it's lure will run the risk of being
pounced upon by a predator either too large for it to eat or otherwise a danger
to the snake.
way of example a 100 gram bird pouncing on a young Death Adder's tail, (noting
the snake may weigh less than 10 grams for some months after birth), may well
grab the tail (and snake) and cause fatal injury to it. A small snake biting the head of the incoming
bird will not be able to stop the juggernaught of a 10 times larger bird
heading straight for the tail.
the snake may bite the bird, perhaps ultimately causing it's death, this would
probably not stop the snake receiving one or more potentially fatal bites
contrast a 100 gram bird tackling the tail of a Death Adder itself weighing two
or three times this is likely to find itself easily grounded by a sharp bite to
terms of even larger birds or mammals, these are not usually insectivorous and
hence a caudal lure on a Death Adder of any size is unlikely to attract their
attention in terms of potential food.
larger Death Adders may also be able to better fend off unsuitable animals
attracted by their caudal luring.
other words the only conclusion that can be drawn is that caudal luring may be
a hazard for small Death Adders. There
appears to be no other basis for explaining why younger specimens don't do it
as often as larger ones.
C., Murphy, J. B. and Carpenter, G. C. 1978. Caudal luring in the Death Adder (Acanthophis antarcticus (Reptilia,
serpentes, elapidae)). Journal of
Boyer, D., Lee, R., Murphy, J. B. and Radcliffe, C. W. 1990. Caudal luring in
the southern death adder, Acanthophis
antarcticus. Journal of Herpetology 24(3):253-260.
Hoser, R. T.
1989. Australian Reptiles and Frogs.
Pierson and Co., Sydney, NSW, Australia:238 pp.
Hoser, R. T.
1995. Australia’s Death Adders, Genus Acanthophis.
The Reptilian 3(4):7-21 and cover,
Hoser, R. T.
2002. Death Adders (Genus Acanthophis):
An updated overview, including descriptions of 3 new island species and 2 new
Australian subspecies. Crocodilian -
Journal of the Victorian Association of Amateur Herpetologists
4(1):5-11,16-22,24-30, front and back covers.
Worrell, E. R.
1972. Dangerous snakes of Australia and
New Guinea. Angus and Robertson, Sydney, Australia. 65 pp.