That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

While most people acknowledge that spiders perform a valuable service by consuming harmful insects, there remains the lingering belief that the vast majorities are dangerously venomous, and do more harm than good. Today I’d like to pass along some facts and figures that you may find interesting.

Venom

All spiders produce venom, but in most cases it is only potent enough to overcome the invertebrates upon which they feed. Less than 1% of the world’s 40,000+ spider species are capable of delivering a dangerously venomous bite to humans.

The Real Killers

Dogs, horses, pigs and other domestic animals, although enjoying a far more favorable reputation than spiders, actually kill and maim many more people than do our 8-legged neighbors. In fact, far more people are killed yearly in the USA by falling vending machines (I’m guessing in bars?) than by spiders or snakes!

Potentially Deadly Spiders

The most highly venomous Arachnid, Australia’s funnel-web spider (Atrax robustus), has not caused a fatality since the introduction of antivenin in 1981. In the USA, widows (Latrodectus spp.) and the brown recluse spider (Loxosceles reclusa) are potentially dangerous, but antivenin is available. The bite of the world’s largest spider, South America’s 12-inch goliath bird-eater (Theraphosa blondi), is very painful but otherwise harmless.

Other Spider-Associated Risks

The foregoing should not be taken as a license to ignore caution when dealing with spiders. Just as with bees and other venomous animals, allergic persons can be killed by the bites of relatively benign species, and dangerous infections can be associated with the bite of any animal. Many tarantulas shed urticating hairs when disturbed or even when just moving about. A colleague of mine underwent major surgery to remove such hairs, deposited on his hand by a “tame” red-kneed tarantula, from his eye.

I have kept native and exotic spiders since childhood, and have never been bitten because I do not pick up spiders with my hands. I urge you to handle spiders, if at all, with a plastic tongs or by ushering them into a container.

Further Reading

An excellent resource for those interested in spiders, the American Museum of Natural History’s World Spider Catalog is published at http://research.amnh.org/entomology/spiders/catalog/.

Please see my article Tarantulas in Captivity for information on keeping these fascinating creatures at home.

Funnel Web spider image referenced from Wikipedia and originally posted by Zinnmann

Goliath Bird Eating Spider image referenced from Wikipedia and originally posted by Dcoetzee

Aeromonas hydrophila is a common species of gram negative bacteria that often infects captive frogs and salamanders. It is particularly prevalent during the warmer months, when high temperatures stress amphibian immune systems (even tropical species often spend much of their time in cool micro-habitats) and leave them vulnerable to microorganisms that might otherwise have been resisted. Aeromonas infections are usually referred to as “red leg” or “Septicemia”.

Symptoms

Red leg, so named because the red lesions associated with it often first appear on the skin where the rear legs meet the body, is contagious and can be transmitted by contact with infected water, animals, wood, etc. The skin hemorrhages that typically occur become progressively deeper and the skin eventually sloughs off. Afflicted animals may also twitch, convulse, and become comatose. If not treated in its early stages, the condition is almost always fatal.

Improved sanitation is an immediate first step to take. Hands must be washed after handling animals and enclosures, for your own and your collection’s benefit. Environmental conditions such as poor hygiene will contribute to Aeromonas outbreaks, as will overcrowding.

Refrigeration as Treatment

Red leg is sometimes cured or by refrigeration at 39 to 41°F for two weeks. This treatment, pioneered in laboratory colonies of leopard frogs, has also been successfully used with Mexican axolotls. It appears that the immune systems of some amphibians function more effectively at low temperatures, while Aeromonas bacteria does best under warmer conditions.

The beneficial effects of low temperatures are not limited to red leg alone…while working at the Bronx Zoo I twice submitted “dead” salamanders (a mudpuppy and a hellbender) for necropsy, only to find them alive and well after a night in the animal hospital’s refrigerator!

Medical Treatment

When working with animals afflicted by any type of infection, it is very important that you contact your personal physician for advice concerning possible health risks to you and other members of your household.

While lacerated skin would lead one to believe that Aeromonas is the culprit, a definite diagnosis can only be made by blood culture performed by a veterinarian. This is important because a number of other species of bacteria, including Pseudomonas and Salmonella, may cause similar lesions, and the treatment of each will likely vary. Opportunistic bacteria and fungi, which commonly colonize the open wounds, must also be addressed.

Further Reading

An interesting early case history of a red leg outbreak among captive frogs is posted at https://kb.osu.edu/dspace/bitstream/1811/5136/1/V66N01_087.pdf.

In Part I of this article we discussed the origin and current state of the problems associated with the long term use of goldfishes as a staple food for reptiles and amphibians.

Bait and Tropical Fishes

Fathead minnows, golden shiners and related fishes are preferable to goldfishes as a reptile and amphibian food, and may be used as dietary staples where appropriate. They are generally raised in outdoor ponds or wild-caught, and have fed on a variety of invertebrates, plants and other natural food items. This renders them a highly nutritious food item.

Whenever possible, you should alternate the species of fish offered. This is especially important for water and tentacled snakes, mata mata and alligator snapping turtles, Surinam toads and other species that feed primarily upon fish. Many common pet trade tropical fishes are nutritious and easily-reared, including swordtails, platys, guppies and mollies.

Food Market Fishes

Food market fresh water fishes (i.e. Tilapia and catfish), especially those which can be obtained whole, are another useful option. I fed the Bronx Zoo’s gharials (large, piscivorous crocodilians) on trout for many years…but that cost upwards of $1,000/month – 20 years ago!

Collecting Native Fishes

Where legal, you can add vital nutrients to your pets’ diets by collecting freshwater fishes via seine net, trap or pole. I always remove the dorsal and pectoral spines of catfishes, sunfishes and other well-armed species, just to be on the safe side.

Fish and Vitamin E

The Vitamin E question has also been investigated…I’ll write more on that in the future. For now, please be aware that frozen fish of any kind, used as a dietary staple for crocodilians and turtles, has been implicated in Vitamin E and other deficiencies. Marine fishes, frozen or fresh, seem to block vitamin absorption when fed in quantity to fresh water animals.

Further Reading

I must say that, food considerations aside, I like goldfish! Please check out our blog article Carnival Fish for some interesting background on their habits, care and long history as pets.

The books Snakes: the Keeper and the Kept and Snakes and Snake Hunting, written by Staten Island Zoo curator Carl Kauffeld, turned “Okeetee, South Carolina” into a household name for legions of snake enthusiasts worldwide (myself included). An incredibly productive snake collecting area, Okeetee was especially noted for its brilliantly colored corn snakes, Elaphe (Pantherophis) guttata, and abundant Eastern diamondback rattlesnakes (Crotalus adamanteus). A road sign from the area still graces the corn snake exhibit at the Bronx Zoo, where I worked for many years, and photographs taken from collecting trips to Okeetee in the 60’s and 70’s line the back rooms of the zoo’s 100 year old reptile house.

The Influence of Okeetee

These “Okeetee corns”, as they became known, were largely responsible for the explosion of interest in captive snake breeding in the late 60’s and 70’s, and ushered in a new age of husbandry innovations; today the corn snake remains the world’s most commonly bred snake species. Corn snakes have provided untold numbers of aspiring herpetologists with an introduction to snake keeping and snake breeding, and have played an important role in a number of research efforts.

Preparing Snakes for the Breeding Season

For those of you who plan to breed corn snakes, now (late summer) is the time to begin preparations. Your snakes should be fed heavily until autumn, at which time they can be chilled to 50-59 F (after a 2 week fast) for 6-8 weeks. Although corn snakes may reproduce at the tender age of 11 months, breeding should be withheld until they are at least 2 years of age…females that are bred too early often fail to attain full size, and tend to produce small clutches and weak offspring.

Mating occurs from March to June in most regions, with the eggs being laid 25-50 days thereafter. A second clutch may be produced in late summer/early fall. An average clutch consists of 16 eggs, but may range from 6-26. At 82 F, incubation time averages 62 days in length, and the young are 8-11 inches long upon hatching.

As we will see in Part II of this article, years of intense captive breeding efforts have produced a mind-boggling array of corn snake morphs, strains and hybrids. The reproductive cycle of all parallels that just described, but individual details, such as clutch size, etc., will vary among the various types of corn snakes.

Further Reading

The Southwestern Center for Herpetological Research has posted some informative notes and blog entries concerning the influence that Carl Kauffeld and Okeetee, SC have had on the snake-keeping community:
http://southwesternherp.com/cgi-bin/yabb2/YaBB.pl?num=1215719054.

The care of corn snakes roughly parallels that of black rat snakes. Please see my article The Captive Care of Black Ratsnakes for more information.

I remember well my shock when the news concerning temperature dependant sex determination (TDSD) among reptiles first broke.  Imagine…a turtle or crocodile egg can develop as either a male or female, depending upon the incubation temperature!  Well, it now seems that at least one species of lizard, the three-lined skink (Bassiana duperreyi), complicates matters even further.

Egg Size and Sex

Writing in the June, 2009 issue of Current Biology, University of Sydney biologists have revealed that large skink eggs develop into females, while small eggs become males.  Furthermore, removing yolk from a large egg resulted in a male hatchling, despite the fact that female genes were present; adding yolk to a small egg over-rode the effect of the male genes already in the egg, producing instead a female.

Temperature and Sex

Extreme nest temperatures, it seems, can also affect the hatchlings’ sex, regardless of its genetic makeup, resulting in xx chromosome males (males are usually xy) and xy females (females are typically xx).

Survival and Conservation Implications

The question that begs answering, of course, is why has this lizard evolved such a unique and complicated reproductive strategy?  Researchers are now looking into its ecology to determine the answer.

Understanding such matters has greatly assisted those working to conserve reptiles and amphibians.  Knowing the parameters of TDSD has allowed us to pick and choose the sexes of highly endangered species being bred in zoos, so that a favorable sex ratio can be maintained.

Of course, there were some problems early on.  I was working with green sea turtle head-start programs in Costa Rica when TDSD first came to light.  The organization I was with had been gathering sea turtle eggs for 30 years, incubating them, and then releasing the young when they had grown past the vulnerable stage.  Great in theory…but by using a single incubation temperature, we may have produced only female green turtles for the entire 3 decades!

Further Reading

You can read more about the natural history of the three-lined skink and its relatives at http://www.jcvi.org/reptiles/species.php?genus=Bassiana&species=duperreyi.