“Spreading Adders”

April 29th, 2010

The hiss of an Eastern hog-nosed snake as it spreads its neck and acts like a cobra can be quite startling, but it is all bluff. Eastern hog -nosed snakes are completely harmless, and it is nearly impossible to get one to bite. It is no accident that they seem to show up when toads are active. Hog-nosed snakes specialize on toads, eating almost nothing else. Colors and patterns of hog-nosed snakes vary from nearly all black to reddish with various shaped markings, and younger hog-nosed snakes seem to be brighter in color than older and larger ones.

An adul;t (top) and juvenile (bottom) Eastern hog-nosed snake

An adult (top) and juvenile (bottom) Eastern hog-nosed snake

When first disturbed, hog-nosed snakes go through their hissing and spreading display, hence the nickname “spreading adder.” However, if they are bothered a bit more, they switch their behavior to a ridiculous series of movements in which they appear to act as though they have died, going so far as to roll over on their back, open their mouth, drag their tongue in the dirt and lay there motionless. If you wait a few minutes, they will roll their head over and look at you. If you roll them over so that they are upright, they quickly roll back over upside down. And, if you wait long enough, they roll over and crawl away. What could possibly be the advantage of doing this? One would think that simply lying there would make it easier for a predator to eat them.

Starting in the bottom left, follow clockwise, the deith-feigning sequence of a hog-nosed snake

Starting at the bottom left, follow clockwise, the death-feigning sequence of an Eastern hog-nosed snake

If you watch carefully when hog-nosed snakes first start rolling over, you will notice that they cover themselves with bodily wastes released from their cloaca as they twist and coil during their death feigning act. Recall that they eat toads, almost exclusively. Toads eat ants and beetles that produce chemicals (alkaloids) for defense, and toads in turn produce strong chemicals that are released from the large glands (paratoids) just in back of their head that make them very bad tasting and sometimes toxic (don’t lick a toad!). So, when Hog-nosed snakes eat toads, they are also eating a bunch of very bad-tasting chemicals. By covering themselves with excrement, Hog-nosed snakes make themselves very bad to eat. The “playing dead” likely keeps them from being injured while a predator determines that they are not as tasty as they first appeared to be when they were crawling along.

Threat display of an adult Eastern hog-nosed snake. Note the raised tail and the flattened neck, hence, "spreading adder."

Threat display of an adult Eastern hog-nosed snake. Note the raised tail and the flattened neck, hence, "spreading adder."

Mole salamanders

April 21st, 2010

In an earlier blog, we mentioned that Spotted salamanders (Ambystoma maculatum) were making their way into ponds to breed. We thought that we might tell you about not only Spotted salamanders but also about the family of salamanders that they belong to, the Ambystomatidae. These amphibians are collectively known as “mole” salamanders because they spend much of the year underground. This family is distributed throughout most of North America and contains 37 species. Oklahoma has six species.

Four of the six species of mole salamanders in Oklahoma

Four of the six species of mole salamanders in Oklahoma

Among the Oklahoma species of mole salamanders, some breed in late winter, like the Spotted salamander and the Small-mouthed salamander (A. texanum), some breed in fall, like the Marbled and Ringed salamanders (A. opacum and A. annulatum, respectively), and some breed in spring, like the Tiger and Mole salamanders (A. tigrinum and A. talpoideum, respectively). When they are breeding, many hundreds seem to appear from nowhere. Considering how many arrive at the breeding ponds, it seems that they could be found any time during the remainder of the year—not so! After adults breed in ponds, they leave the ponds and go underground, not to be seen until the next breeding event. Obviously, they must feed while underground in order to grow and save energy to reproduce next time, but very little is known about their underground activity. Some, like Tiger salamanders, are known to live in gopher burrows, often in large numbers, but for the rest, we know very little.

After the breeding events, eggs hatch in ponds, and thousands of tiny salamander larvae emerge. Larvae of all species of mole salamanders look superficially alike, and a bit of skill is required to identify the different species in larval form. They have external gills, a laterally compressed tail that aids in swimming, and when not slowly walking on the pond bottom, they swim with an undulating motion, similar to that of alligators. Temporary ponds are filled with tiny invertebrates, collectively called microinvertebrates, such as ostracods, copepods, and Daphnia (a genus of cladocerans). Larvae of mole salamanders vacuum up these tiny invertebrates by opening the mouth and expanding the throat at the same time. They close the mouth and expel the water out through the gill slits, but retain the prey items. Their diet includes nearly every kind of pond organism small enough to fit into their mouths.

Larvae of Mole salamanders grow rapidly, but should rain be scarce, their pond might dry up before they are large enough to transform into adults. Ponds are also filled with predators that eat salamander larvae, including watersnakes, bullfrogs, giant waterbugs, and larvae of dragonflies and predaceous diving beetles. Some species of birds also visit ponds and capture salamander larvae. As salamander larvae grow, it is less likely that they will be captured and eaten by an insect. Large larvae are particularly attractive to birds and snakes. Life in the pond is risky for salamander larvae, and the best thing to do is grow fast and leave the pond as quickly as possible.  Of the thousands of eggs that are deposited each year, some will survive to become adults and breed, and most won’t. Variation among individual offspring sets the stage for natural selection.

Larva of a Tiger salamander

Larva of a Tiger salamander

The First Spring Rains Bring Out Frogs and Salamanders

April 21st, 2010

Rains that occurred several weeks ago in southeastern Oklahoma brought out all of the early spring frogs, including Spring peepers (Pseudacris crucifer), Cajun chorus frogs (Pseudacris fouquettei), Pickerel frogs (Lithobates palustris), and Southern crawfish frogs (Lithobates areolata). Even Southern leopard frogs (Lithobates sphenocephala) and American toads (Anaxyrus americanus) were active. In addition to running our traps at our primary research site in Le Flore County, we spent time driving roads at night in both Le Flore and McCurtain Counties. Nearly every roadside pond contained some mix of the above frog species. The only two that did not occur together were Pickerel and Crawfish frogs.

An adult Cajon chorus frog

An adult Cajun chorus frog

A number of amphibian species in Oklahoma breed during late winter and early spring, and their nearly deafening choruses can be easily experienced by driving around in rural areas at night. Males congregate in ponds when rains first begin, and their calls attract females that have spent the fall and winter converting energy that they stored from spring, summer, and fall activity into eggs. Examination of ponds during the daytime usually reveals many egg masses attached to vegetation or floating on the pond surfaces.

In addition to frogs that reveal their presence by calling, salamanders are moving into ponds to breed. We found large numbers of Spotted salamanders (Ambystoma maculatum) moving across roads heading for ponds during rains, and we captured some in our traps. Unlike frogs, salamanders do not vocalize. Whereas female frogs are attracted to individual males by the quality of the call, female salamanders are attracted to individual males by the quality of their courtship behavior.

An adult Spotted salamander

An adult Spotted salamander

So, for those of you are interested in amphibians, drive around in rural areas when it begins to rain and listen for frog choruses.  With the windows cracked, you can hear choruses in breeding ponds along the roads.  If you find a chorus on public property, put on your boots, turn on your good flashlight or headlight (preferred), and see if you can locate individual frogs that are calling. Chorus frogs are tiny and usually call inside grass clumps at the surface of the water. A Chorus frog calling right at your feet can be difficult to locate and requires persistence. If you are lucky enough to hear the low snoring calls of Pickerel or Crawfish frogs, you will need to move slowly without sloshing the water.  Even slight movement of the water caused these wary frogs to stop calling and dive below the surface. If you stand quietly for ten minutes or so, males will reappear and begin calling.

Sirens galore!

April 20th, 2010

Several weeks ago, a group from the museum visited the ODWC’s Red Slough in search of some salamanders that only occur in swamps of the southeastern part of Oklahoma. We were able to trap more than 20 sirens, which are elongate, eel-shaped salamanders that live their lives in water. They are in their own family, the Sirenidae, and the species that occurs in Oklahoma is the Western lesser siren, Siren intermedia.

Adult Lesser siren

Adult Western lesser siren

Unlike eels, sirens have external gills and a pair of tiny front legs, that on first glance, appear useless. Believe it or not, they use these legs on rainy nights when they move short distances across land. These sirens can reach eight inches in length, but most are slightly smaller. In most salamanders that have aquatic larvae, external gills used for respiration in water are lost when the salamanders metamorphose into terrestrial adults. In sirens, no obvious metamorphosis takes place, with the adults looking exactly like the “larvae,” just larger in size. However, close examination of the internal morphology reveals that reproductive organs develop as the “larvae” increase in size and age. Consequently, they do “metamorphose” but retain some larval characteristics (external gills).

Sirens reach sexual maturity in about two years. They deposit from 100–200 eggs in cavities in mud at the bottom of swamps. One of the most interesting aspects of the biology of sirens is their ability to form a cocoon around their body when swamps dry up. They burrow into the mud and secrete mucous that forms the cocoon, the function of which is to prevent them from drying up. Sirens can remain inactive for as much as eight months in their cocoon until rains fill the swamps that they live in.

Although sirens are difficult to observe because they are under water, they can be easily trapped with minnow traps, and no bait is needed. If you should trap one to observe, be sure to keep it in water that contains oxygen and is not chlorinated. It might also be useful to drop a few dried pine needles or oak leaves into the aquarium as tannins released from needles and leaves can keep mold from attacking the skin of sirens and other aquatic amphibians and reptiles.

Head of Lesser siren showing external gills

Head of Western lesser siren showing external gills

Blog Readers, we are back!

April 20th, 2010

Just after our last blog, rains brought frogs and salamanders out all over the place, which sent us racing around different parts of southeastern Oklahoma. We also ran our drift fence traps at our field site in Le Flore County, trying to keep up with movements of amphibians. A brief trip to Florida to present a talk to one of the Florida herpetological societies in Gainesville interrupted our amphibian and reptile excursions in Oklahoma, but only for about a week. As a result, we have been so busy that we have not been able to keep up with our blog. However, as the title says, we are back, and we will try to catch you up on what we have been doing in the following series of blogs. We hope you will all stick with us, and many thanks for all of your kind comments.

Late Winter Frogs Will Begin Breeding Soon

January 26th, 2010

We are eagerly awaiting the first calls of the late winter-breeding Cajun chorus frogs (Pseudacris fouquettei), Spring peepers (Pseudacris crucifer), and Pickerel frogs (Lithobates [Rana] palustris). These frogs begin migrating to ponds, roadside ditches, and marshy areas with the first sign of warming weather and substantial rainfall. Spring peepers and Pickerel frogs occur only in the eastern third of Oklahoma, whereas various species of Chorus frogs occur throughout most of Oklahoma.

The Chorus frogs and Spring peepers are small frogs in the treefrog family (Hylidae). Chorus frogs are brown with darker brown stripes. Spring peepers are yellowish, with an irregular X on the back, from which the name, crucifer, is derived. Calls of these two frogs are easily distinguished. The Chorus frog call is a slow trill, similar to running a finger over a comb. In contrast, the call of the Spring peeper is a single loud whistle. When numerous individuals of these two species call from the same pond, the sound can be deafening! Males of both species call from perches on shrubs or small trees at the edge of the water or from clumps of vegetation in the water.

Pickerel frogs, which are in the “true” frog family (Ranidae), are moderately large frogs with two rows of squarish spots on the dorsum. Each frog has a different spotting pattern, making it easy to tell individuals apart. Pickerel frogs typically begin breeding in middle to late February, continuing into March. Their call is a low snore and can be difficult to hear if they are breeding in the same ponds as the louder Chorus frogs and Spring peepers. In addition, Pickerel frogs sometimes call under water, muffling their sound even more.

More to come when the frogs start breeding!


A male Cajun chorus frog calling


Adult Spring peeper


Male (top) and female (bottom) Pickerel frog in amplexus

Backtracking to Fall Breeding

December 18th, 2009

During Fall, when temporary ponds fill with water in southeastern Oklahoma, thousands of Southern leopard frogs come in to breed. Males enter the ponds at night, usually when it is raining or within several nights following the rain. Males call to attract females, and, after a female selects the male with which she will mate, the frogs amplex. Although amplexus varies among frog species, Southern leopard frogs amplex with the male on top of the female with his front legs wrapped on the body of the female just behind her front legs. This is called inguinal amplexus because of the position of the male’s front legs. As you probably know, fertilization is external in almost all frogs, so the male releases sperm over the eggs as the eggs are being laid, fertilizing the eggs. The eggs are laid in a mass attached to vegetation in the water. If the pond doesn’t dry up, the eggs hatch into tiny tadpoles. Temporary ponds are usually rich in nutrients in Fall, and as a result, most surfaces in the ponds are covered with algae, and huge populations of various insects and other invertebrates build up as time goes on. The tadpoles feed on algae, scraping it off of the surfaces with tiny teeth surrounding the mouth. Because tadpoles of Southern leopard frogs are vegetarians (herbivores), nearly all of their digestive system is intestine.  If you closely examine a tadpole, you can see the intestine through the skin. Once tadpoles hatch from eggs, the real race begins. Individual tadpoles face an uncertain future. The pond can dry up before they transform into a terrestrial frog. Also, aquatic birds and many insects, including larvae of dragonflies, damselflies, and predaceous diving beetles, eat tadpoles. Tadpoles eat and grow as fast as they can so that they can get out of the pond before it dries and so that they can get bigger than some of their predators (aquatic insects). One of the particularly fascinating things about frogs is the remarkable change in lifestyle that goes with transformation from a tadpole to a young frog. This will be a topic for a future blog, so keep posted.

Hoping for Rain—Southern Leopard Frogs

December 18th, 2009

Usually during this time of year (December), we don’t think about amphibians or reptiles because most are spending the winter hidden to avoid freezing temperatures. However, Southern leopard frogs (Lithobates [Rana] sphenocephala) breed both in Spring and Fall in temporary ponds. As a result, ponds that retain water in late Fall and early Winter in eastern Oklahoma contain tadpoles of Southern leopard frogs. As the ponds shrink in size, the tadpoles become easy prey for herons and other water birds. In addition, as temperatures go down and the ponds shrink, the possibility exists that the ponds might dry up or freeze solid, killing the tadpoles. One such pond at our research site in Le Flore County is now filled with tadpoles and the water is dangerously low. Although it might seem that producing tadpoles when the possibility exists that the ponds might dry up or freeze is not in the best interest of the individual frogs that deposited the eggs, that is actually not the case. These frogs cannot predict whether ponds will last long enough or be refilled. However, one thing is for certain—if they do not breed at all, then there is no possibility that they will produce offspring in the event that ponds do last long enough in a particular year. Also, they can try again in Spring, and if they survive the Summer, yet again the following Fall. So, in effect, they are hedging their bets. Individual frogs that breed in Fall have some chance that they will produce offspring that will survive, whereas individual frogs that do not reproduce in Fall absolutely produce no offspring.

Adult Southern Leopard frog from southeastern Oklahoma

Adult Southern Leopard frog from southeastern Oklahoma

Velvet-tails and Coon-tails

October 28th, 2009

Timber Ratlesnake or "Velvet-tail" (left) and Western Diamondback or "Coon-tail" (right).

Adults of the Timber Rattlesnake or "Velvet-tail" (left) and the Western Diamondback or "Coon-tail" (right).

Two common rattlesnakes, the Timber Rattlesnake (Crotalus horridus) and the Western Diamondback (Crotalus atrox), are known to many locals as Velvet-tails and Coon-tails, respectively. The reasons—Timber Rattlesnakes have black tails that have a velvety appearance, particularly just after they shed their skin, and Western Diamondbacks have black and white banded tails similar to those of raccoons. Both of these snakes can be considered very dangerous because they have toxic venom, and they can reach large sizes and thus produce a lot of venom.

Most commonly seen in Spring and Fall, both species aggregate in den-sites to overwinter, and both species bask in the open (often on dirt or paved roads) to gain heat on cooler days. These snakes are native to Oklahoma, with Velvet-tails occurring in the eastern half of the state and Coon-tails occurring across most of the state. Extreme care should be taken when relocating or handling these snakes, and our best advice is to leave them alone. The good news is that if one shows up in your yard, it is likely just passing through and will be gone in a few days.

Disappearing Snakes

October 28th, 2009

As the weather cools off in late fall, most snakes disappear, seeking refuges in which to spend the winter. In our amphibian and reptile studies in southeastern Oklahoma, we have captured very few snakes during the last two weeks. Only two were captured during the third week of October, and both were juveniles. One was a young Eastern Racer (Coluber constrictor) and the other was a young Prairie Kingsnake (Lampropeltis calligaster). Both of these are common snakes, but most people do not see Prairie Kingsnakes very often because they are nocturnal and very secretive. Eastern Racers, on the other hand, are very common, and the are the most frequently seen snakes crossing roads during Spring, Summer, and Fall, but only during the day. Because they are very wary and slither rapidly, they are difficult to catch. In addition, when grabbed, the frequently bite! The good news is that they are non-venomous and they are only biting because they are frightened. They are completely harmless, and like most nonvenomous snakes, their bites do not cause infections.


Juvenile Eastern Racer (left) and Prairie Kingsnake (right).