Mallee Worm-Lizard (Aprasia inaurita), family Pygopodidae, Northern Yorke Peninsula, South Australia

Pink-tailed Worm-lizard (Aprasia parapulchella), family Pygopodidae, SE Australia

Legless lizard.

Every so often I’m asked about the difference between snakes and “legless lizards”.  This question is usually asked wanting to know whether or not the animal in their garden is likely to kill them, but also out of general curiosity.

Snakes are very interesting animals and arouse interest (or fear) in just about all members of the community. Most people have a “snake story”, be it a positive or a negative one. Often the interest stems from the fact that some snakes are deadly (we've a lot of potentially deadly ones in Australia) or simply that they are such bizarre animals. Getting around without limbs is tricky enough, but eating an item larger than your head without using hands is downright crazy. Whatever the reason they are certainly different from most “regular” animals. There are quite a few snake-like lizards that are commonly encountered so without getting too technical, here are some of the main differences between the snake and the lizard. 

Difference 1: No legs.

The most apparent “snakey” trait is the lack of limbs and elongation of the body. 

Elongations and limblessness in reptile has evolved independently several times and is seen in several different groups. This trait probably evolved as it allowed animals to burrow, enabling them to escape from predators and perhaps select appropriate temperatures.  Sand-burrowing Lerista skinks (lizards) have severely reduced limbs, with several species being totally limbless. 

below: A Lerista distinguenda showing a reduction in limb size (whilst still retaining 4 limbs). 

below: Lerista praepedita is a sand dwelling burrower that has completely lost it's fore-limbs and the hind-limbs are reduced to tiny stumps. 

Moving rapidly through thick vegetation is probably aided by a reduction in limb size, as seen in the Pygopodid group  (essentially a group of limbless geckos). These limbless lizards all have a vestige of the hind limb, something that snakes do not often have.  This vestige is usually in the form of a stump, a small bud or a flap of skin. Some "normal" lizards that inhabit the same areas exhibit a reduction in limb size. 

below: You can make out the vestigial limb buds on this Hooded Scaly-foot lizard Pygopus nigriceps

below: This Perth Slender-bluetongue Cyclodomorphus celatus has small limbs, probably owing to the dense heath it inhabits and it's tendency to burrow under loose sand.  

Difference 2: No ears

Snakes can’t hear. No ears, no ear-drums. Most legless lizards have some form of ear opening that is only usually visible on closer inspection.  Some of the subterranean specialists, the worm-lizards Aprasia have lost their ear-openings, presumably as this is a place dirt and sand will gather and ants can attack (they eat ants eggs, and the ants hate it).

below: No ears on this potentially deadly Dugite Pseudonaja affinis 

 below: This Worm-lizard Aprasia repens has no ears BUT it's still a lizard!

below: You can clearly see the ears on this Fraser's Legless Lizard Delma fraseri (also dust spots on my sensor)

Difference 3: No eye-lids

Snakes have a single fixed transparent “spectacle” whereas most lizards have a movable eye-lid. Geckos, of course, buck this trend and also have a single fixed spectacle. They often use their long fleshy tongues to clean their eyes and faces after feeding. This is also true of the Pygopodids (remember the legless lizards of gecko origins?). Again, this trait has also evolved independently in some skink species (both limbed and limb-less).

 below: This Spiny-tailed gecko Strophurus spinigeris cleans it's spectacle with it's tongue. 

below: The Granite Worm-lizard Aprasia puchella has reduced extremities (ear, limb buds) to reduce surfaces ants can attack. No eye-lids would also help.

Difference 4: Tongues

Legless lizards tend not to flick their tongues much at all and when they do it’s not a spectacular fork like that of a snake. Legless Lizards have thick fleshy tongues that often have a shallow fork at the tip (at best).  Snakes use their tongue to “smell” prey or threats so they are constantly flicking it in and out. This has to do with the tongue picking up scent particles on each “fork”.  

below: A 221cm Mulga Snake Pseudechis australis shows off it's tongue in a threat display. 

So powerful is the image of a long, thin animal flicking it’s tongue out, that several of the Pygopodids have incorporated this behaviour into their threat display. As well as looking more or less like a snake, many of the Delma  and Pygopus genus have black banding across the back of the head, markings that mirror the potentially fatal Western Brown Snake Pseudonaja mengdeni/asphydorhyncha/nuchalis or young Eastern Brown Snake Pseudonaja textilis.  Even with their slightly forked fleshy tongues, these legless lizards put on an impressive display and makes all but the most experienced herpetologists second-guess the animal they were about to grab.

 below: This young Dugite Pseudonaja affinis has slight banding across the head, a characteristic shared by many of the brown snakes and mimicked by some Pygopodids.

below: This Hooded Scaly-foot lizard Pygopus nigriceps bears the dark markings across the nape and head, possibly to mimic the deadly brown snake Pseudonaja sp. 

below: This Burton's Legless Lizard Lialis burtonis uses it's tongue to clean it's face. It's tongue is slightly forked.

below: This Common Scaly-foot Lizard Pygopus lepidopodus cleans it's face with it's thick fleshy tongue.

Of course, you don’t need to be a snake to have a heavily forked tongue. All goanna species have a heavily divided forked tongue.

below: the splendidly forked tongue of a Heath Monitor Varanus rosenbergi 

  Difference 5: Tail-Body ratio.

This is pretty basic. Snakes have a very long body and a comparatively short tail.  To clarify, the tail begins when the body ends, at the cloaca (the multi-purpose orifice for sex/defecation/laying eggs). In a snake, this is usually about 10% of the body length from the very end of the animal (tail tip). As elongation has evolved independently in various groups, the lizards are quite different. Instead of a long elongate body, their body is relatively short with an extremely long tail (up to and exceeding 200% of body length in some Delma species). The legless skinks are similar, having very long tail lengths in respect to body length.  Here’s where it can get tricky. Legless lizards can “lose” part of all of their tail (caudal autonomy) so in growing it back can have a relatively short tail.

 below: The cloaca of this burrowing snake SImoselaps semifasciatus is clearly visible.

below: The Stimson's Python Antaresia stimsoni has a long body and a short tail. 

below: This Fraser's Legless Lizard Delma fraseri has a massive tail compared to body length.

  In conclusion:

There are no hard and fast rules in regard to these differences. As stated there are exceptions to each difference. With a bit of practise it’s fairly easy to pick a lizard and a snake. Once initiated to looking for certain characteristics, you’ll wonder how anyone has trouble differentiating the two groups.

below: The Tiger Snake Notechis scutatus is quite striking and difficult to confuse with anything else. 

below: You'd have a hard time confusing this Granite Worm-lizard Aprasia puchella with a snake.

Want to look at more pictures of snakes/legless lizards etc etc?

Snakes: 

http://www.pbase.com/nephrurus/pythons__pythonidae

http://www.pbase.com/nephrurus/blind_snakes__typhlopidae

http://www.pbase.com/nephrurus/colubridae

http://www.pbase.com/nephrurus/elapidae

Legless geckos: Pygopodids

http://www.pbase.com/nephrurus/legless_lizards__pygopodidae

Legless Skinks:

http://www.pbase.com/nephrurus/coeranoscincus_sp

http://www.pbase.com/nephrurus/lerista_sp

Goannas and Monitors: