Amphibians (Class Amphibia)
Amphibians live part of their life cycle in the water and part on land.
This dual nature is the reason why these animals exhibit such diverse ways to reproduce. More primitive families of salamanders have males that release sperm in water near the eggs (external fertilization). In other families, males transfer sperm into packets called spermatophores , which are picked up by the female during courtship (internal fertilization). In frogs, sperm is usually deposited on the eggs. Most amphibians lay their eggs in fresh water or on land, but others are viviparous, meaning the babies grow within the mother's body and are born live. Frogs are among the most prolific breeders and can lay anywhere from 1 egg to 25,000, while salamanders lay a few dozen. Some frogs and salamanders defend their eggs and may carry eggs or tadpoles on their backs. For species which practice internal fertilization, females guard the eggs. For eggs that are externally fertilized, males guard and defend the eggs within their territory. In fact, paternal care is most common in fish and amphibians and not mammals!
Amphibians are best known for their amazing transformation from larvae to adults known as metamorphosis. How long metamorphosis takes varies. Some frog larvae born one summer may not transform until the following summer. However, tadpoles of toads living in deserts may transform in only 8 days.
Like some reptiles, amphibians can change colors to help regulate their body temperatures with darker colors absorbing more light. Some colors and patterns help hide amphibians from predators and are called crypsis. Others have skin toxins that are irritating or deadly to predators. Some frogs have color patches on their flanks or posterior sides of their thighs. Biologists think that when frogs jump, the color distracts a predator’s attention long enough to allow the frog to escape.
Salamanders and Newts (Order Caudata)
358 species worldwide, 21 species in Maryland
Salamanders and newts are nocturnal and secretive animals with long slender bodies, long tails and in most cases, two pairs of legs. Life cycles of salamanders and newts vary with the animal and include those that are totally aquatic, totally terrestrial, and both --spending time on land and water. Habitats include rivers, lakes, streams, ponds, swamps, underground caves, under rocks and logs; some species burrow and some climb trees. Their skin is actually a respiratory surface – its moist surface allows air to pass through - and the outer layer is frequently shed and usually eaten. Salamanders and newts eat a varied diet including small invertebrates, insects, slugs, snails, and worms. They in turn provide food and are eaten by shrews, birds, snakes, other salamanders, beetles, centipedes, and spiders.
Biologists studying newts and salamanders have found that many of these animals have remarkable orientation and homing abilities. These animals can disperse from their birth places to several kilometers away or more. Other studies demonstrate that individuals, if moved, are able to find their way back to the exact stretch of stream where they were caught. Vision and smell seem to be important to navigation but even blind individuals find their way. Biologists theorize that the pineal body in the brain is sensitive to light and aids these animals in navigating by cueing them in to the sun’s position in the sky even on cloudy days. Other studies have shown that cave salamanders and red-spotted newts can detect the earth’s magnetic field and will use it was a navigation cue.
Frogs and Toads (Order Anura)
3,494 species worldwide, 20 species in Maryland
With nearly 3,500 species worldwide, frogs and toads are the most diverse segment of amphibians. What distinguishes them physically from salamanders and newts is their lack of a tail in the adult stage, which is quite unusual for an animal with a backbone. Biologists believe that natural selection favored tailless adult frogs because they jump and a tail would hinder an animal that utilized a jumping form of locomotion (except, of course, for kangaroos). Frogs that live mainly in the water have long slender bodies and limbs while those living on land burrow and are squat with short legs. Burrowing frogs burrow backwards by shuffling their hind feet sideways so they can watch out for predators at all times. Arboreal or tree-living frogs have disks on their feet that act like suction cups, which allow them to cling to steep sides and even walk upside down on the undersides of plants!
Most of the animals in this group are conspicuous breeders; they search and find mates in large numbers then deposit eggs in easily detected locations. Some groups gather in the hundreds or thousands. Males gather together to call for females and can be heard up to 1 kilometer away. Frogs inflate their vocal sacs during calling, which helps carry the sound through air like the soundboard of an instrument. Three factors that trigger mating behavior include daylight length, temperature, and rainfall. Frogs and toads show site fidelity and come back to same ponds and lakes to breed. Cues that help them find these sites include smell, humidity gradients, landmarks, celestial body positions, magnetic fields, and the calls of other frogs.
Nearly all frogs and toads have a trace of poison in their skin glands. The frog group that has the highest concentration of poison in their skin is the group that includes the brightly colored poison arrow frogs found in Central and South America. As far as we know, these poisons do NOT cause warts.
Photo of Northern Green Frog courtesy of Corey Wickliffe
- Discover Maryland's Herps
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- Maryland Herp Checklist
- Survey Techniques, Collecting Ethics, Safety and the Law
- Problems with Buying Frogs and Tadpoles for Wild Release
- Technical Guide: A Key to the Reptiles and Amphibians of Maryland - 86.3 MB pdf file
- Maryland Amphibian and Reptile Atlas (MARA) Project
- Natural Heritage Program
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The Maryland Herpetology Field Guide is a cooperative effort of the MD Natural Heritage Program and the MD Biological Stream Survey within the Department of Natural Resources and their partners. We wish to thank all who contributed field records, text, and photographs, as well as support throughout its development.