The Complete Guide to Frogs
Frogs are amphibians belonging to the class Amphibia, order Anura, family Ranidae. Adults have no tail, eggs are laid in water and fertilized externally, hatching into tadpoles that breathe with gills. After metamorphosis, adults mainly breathe with lungs and also through their skin. They feed mainly on insects and other invertebrates, and almost all of them are experts at wiping out forest and farmland pests. Let's take a closer look at the complete guide to frogs below!
The Frog's Living Environment
Frogs are ectothermic (cold-blooded) animals with bare skin that cannot effectively prevent water loss from the body, so they cannot live without water or a moist environment throughout their lives. They fear drought and cold, and most live in rainy tropical and temperate regions, with very few species found in the frigid zone. When young, they can only live in water; after growing up, they can also live on land. A frog's respiratory organs are its lungs and skin, while the larval tadpole breathes with gills.
The Structure of a Frog's Tongue
The root of a frog's tongue is at the front of the mouth, with the tip pointing inward, and the tongue is covered in mucus to help catch insects. When swallowing food, it blinks its eyes, and the eyelid closes from the bottom upward. Frogs are omnivorous animals, of which plant-based food accounts for only about 7% of their diet, while animal-based food accounts for about 93%. Their main foods include rice leaf roller, rice stem borer, rice skipper, armyworm, corn borer, pink bollworm, rice caseworm, tobacco cutworm, rice eye butterfly, rice leaf beetle, rice weevil, scarab beetle, ladybug, white-backed planthopper, gray-backed planthopper, black rice bug, brown-backed planthopper, rice leafminer, duckweed midge, fruit fly, mosquito and more.
Reproduction and Development of Frogs
Frogs are dioecious and reproduce by external fertilization; sperm and egg cells complete fertilization in water. The fertilized egg hatches into a tadpole. The newly hatched tadpole has a flat, long tail and breathes through gills on both sides of its head. Once internal gills have developed, the tadpole looks like a fish. The young frog that grows limbs breathes with lungs, has bare skin, and uses the skin to assist breathing. The young frog gradually develops into a frog. The developmental process is: fertilized egg → tadpole → young frog → adult frog.
The Frog's Visual Nerves
The nerve cells in a frog's retina are divided into five types: one type responds only to color, while the other four types respond only to a certain feature of a moving target and can transmit the decomposed feature signals to the visual center of the brain —— the optic tectum. The optic tectum has four layers of nerve cells: the first layer responds to the contrast of a moving target, the second layer can extract the convex edges of the target, the third layer sees only the surrounding edges of the target, and the fourth layer deals only with the light and dark changes at the dark leading edge of the target. These four layers of features are like drawings on four sheets of transparent paper; stacked together, they form a complete image. Therefore, among small animals of various shapes flying rapidly, a frog can immediately identify the flies and moths it likes to eat most, while it shows no reaction to other moving things or stationary scenery.
Morphological Characteristics of Frogs
1. Head: The frog's head is flat, roughly triangular, with a slightly pointed snout tip. The mouth is wide, with a horizontal slit, and is composed of the upper and lower jaws. On the dorsal side of the front end of the upper jaw there is 1 pair of external nostrils, and the outer edge of each external nostril has a nasal valve. The eyes are large and protruding, located on the left and right sides of the head, with upper and lower eyelids, and on the inner side of the lower eyelid there is a translucent nictitating membrane. In male frogs, behind and inside each corner of the mouth there is a light brown membranous fold, the vocal sac, which swells into a bubble shape when calling.
2. Trunk: Behind the frog's tympanum is the trunk. The trunk is short and wide, and between the two legs at the rear end of the trunk, on the dorsal side, there is a small opening, the cloacal opening.
3. Limbs: The frog's forelimbs are short and small, composed of five parts: upper arm, forearm, wrist, palm and fingers, with 4 fingers and no webbing between the fingers. During the breeding season, male frogs have a swollen protrusion on the inner side of the base of the first finger, called the nuptial pad, used for amplexus. The frog's hind limbs are long and well developed, divided into five parts: thigh, shank, tarsus, metatarsus and toes, with 5 toes and webbing between the toes, and on the inner side of the first toe there is a rather hard, keratinized spur.