What Is Amplexus? The Surprising Truth of Frog Mating

Quick Take

• Amplexus can last a few seconds or stretch on for months. What determines the difference will surprise you. See how long it lasts →
• Male frogs have a specialized body part designed purely to keep their grip during mating, though most people have never heard of it. Discover the grip structure →
• A female frog can produce thousands of eggs, yet the survival rate is shockingly low. The numbers reveal just how brutal the odds are. See the survival numbers →
• The dark color of frog embryos isn't just cosmetic. It plays a direct role in their survival in a way most people wouldn't guess. Explore embryo coloration →

Frogs reproduce sexually and most species hatch from eggs. They start the breeding season when the weather begins to warm in late winter or early spring. Although different species have unique approaches to reproduction, for most frogs, there are generally three main stages: finding a mate, amplexus, and spawning. Keep reading to find out what amplexus is and how it is necessary to the frog mating process.

Finding a Mate

During February or March, frogs start emerging from their winter homes, which may include compost ditches, brush piles, burrows, and the bottoms of ponds. Male frogs assemble at different bodies of water to advertise that they are looking for a female. Some species may travel half a mile or farther to reach a specific breeding spot.

When males arrive at the breeding spot, they begin croaking to lure females. The males croak at different pitches and tempos, all through the night if necessary. Frogs make these sounds by closing their nostrils and mouths and moving air forward and backward over their vocal cords. Additionally, this sound can be amplified by drawing in more air and using their vocal sacs to inflate their throat pouch. Males can be very noisy at times, but female frogs are typically quieter, although they may occasionally make the odd grunt.

Amplexus  

If the female is receptive, the male frog will jump on the female’s back and wrap his forelimbs around her body. Next, he will hold the nuptial pads in position. Nuptial pads are textured patches or bumps on the thumbs, hands, or forelimbs of mature male frogs. Most frogs rely on external fertilization, so the nuptial pads help the male remain latched onto the female so he can fertilize the eggs as they are released. This mating position is called amplexus. It can last for just a few seconds or for months at a time, depending on the species. Female frogs will often wait for optimal water and weather conditions, as well as search for the safest place to lay their eggs.

Spawning

The spawning process usually takes place in shallow water. Female frogs can lay thousands of eggs. Northern leopard frogs (Rana pipiens) may lay up to 2,500 eggs, while bullfrogs (Rana catesbeiana) can lay up to 20,000. Frogspawn is laid in the water in large, transparent, jelly-like clumps that contain thousands of tiny black dots. These black dots are the developing frog embryos. The dark color helps the embryos to absorb sunlight, not only keeping them warm, but also accelerating development. Depending on the amount of sunlight the eggs receive and the ambient water temperature, the eggs hatch in around 1 to 3 weeks. Only about 1% to 5% of the spawn survives to become adult frogs.

Metamorphosis

The embryos hatch into larvae called tadpoles. Tadpoles look similar to fish, with long tails and gills to breathe underwater. The metamorphosis from a tadpole to an adult frog is caused by hormones from a tadpole’s thyroid gland. At around 6 to 9 weeks, the tadpole becomes a froglet. Its hind legs begin to emerge, followed by its front legs. It begins to develop lungs so it can breathe air, while the gills are reabsorbed into the body. Its tail begins to shrink, its mouth becomes wider, and it begins to develop a tongue. By around 14 to 16 weeks, they become adult frogs. The tail is fully reabsorbed, and the lungs are strong enough to take over breathing. This is a general time frame for metamorphosis, but each species has its own rate of growth and development.