WHAT DID THAT
SKAAPSTEKER HAVE FOR
DINNER?
R .M . Douglas
Snakes prey on a large va rie ty of insects, birds, m a m m a ls, lizards and frogs. H ow ever, detailed studies on prey species are m o s tly lacking as lite ra tu re reports are u s u a lly vague. S tate m e nts such as, Skaapstekers eat rats or mice, or sim p ly ju s t rodents, abound. P ossibly o w in g to th e fa c t th a t considerable tim e is involved, very little w o rk has been done in the sp ecific fie ld of feeding ecology of snakes. It is im p o rta n t to k n o w w h e th e r a species of snake is an o p p o rtu n is tic feeder o r w h e th e r it is a specialised feeder and o n ly feeds on ce rta in types of rodents or fro g s etc.
The digestive acids o f snakes are e xtrem ely strong, m u ch m ore so th a n in h u m a n s o r o th e r m am m als. Prey item s are to ta lly digested, even bon e s a nd te e th , le a v in g ve ry little fo r id e n tific a tio n purposes. There are, how ever, a fe w item s w h ic h are not digested such as hair, ce rta in p arts o f insects, lizard scales and the snake's o w n teeth w h ic h are s w a llo w e d d u rin g the c o n tin u a l process o f to o th replacem ent or w h e n prey item s are seized and teeth are lodged in the prey.
A sand snake, PSA M M O P H IS sp. eating a mouse.
M edulla (m ultiserial ladder, three row) pattern in the hair of Kreb's fat mouse.
Medulla (alternating uniserial and multiserial two row) pattern in the hair of the Hairy-footed gerbil.
Scale (chevron cuticular) pattern on the h air of Kreb's fat Scale (regular wave cuticular) pattern on the hair of the
mouse. Hairy-footed gerbil.
H a ir fro m stom ach co n te n ts can there fo re be used to id e n tify a snake's diet w ith regards to the kind of m a m m a ls it has eaten. The procedure used to do th is is as fo llo w s : the h a irs fro m the sam ple are placed o n to a slide w h ic h has been covered w ith a th in layer of dissolved g elatin . The g e la tin is a llo w e d to d ry and the h a ir removed fro m the slide. The re su lt is a negative im p rin t of the h a ir in the gelatin . E xam in atio n under a m icroscope o f the im p rin t reveals the c u tic u la r scale patte rn of the hair, w h ic h is d ia g n o s tic of m any species, such as rodents, a lth o u g h in o th e r g ro up s such as the m ongooses very little diffe re n ce betw een the species exist. O th e r facets such as cross sections, m edulla patte rn s, co lo ur, shape and size are ofte n used in c o n ju n c tio n w ith scale im p rin ts to id e n tify an u n k n o w n hair. A fte r
a ll th e above c h a r a c te ris tic s have been considered, cross references o r keys are used to e sta b lish e xactly w h a t the S kaapsteker had fo r d inner.
Hair id e n tifica tio n w as m ost probably firs t used extensively in the anim al fibre in d u stry to d is tin g u is h various types and grades of sheep w ool. It also fo u n d p o p u la rity in the com m ercial furbearer industry. The m ethod has long been used fo r identifying game in poaching and illegal h u n tin g convictions. The id e n tifica tio n of prey species in ow l pellets, jackal and hyaena scats, and other carnivores is yet another area w here the m ethod is used. One of the m ost im p o rta n t areas is in medicine, w here exam ples of prey id e n tifica tio n in rabies control, plague and Lasser fever can be cited. The analysis o f v u ltu re pellets in an th ra x studies has also proved m ost useful. M ore recent app lica tio n s are in the fields of ecology and taxonom y and so the list can go on and on.