If you’ve ever seen a mass of frog eggs floating in a pond or stumbled upon a clutch of jelly-like blobs sticking to vegetation at the water’s edge, you may have wondered if toads also lay their eggs in similar aquatic locations.
As it turns out, while most frogs do reproduce in water, the answer isn’t quite as clear-cut when it comes to toads.
If you’re short on time, here’s a quick answer to your question: Most toads lay their eggs in water, however some species can reproduce on land in damp environments.
Toad Mating and Egg-Laying Habits
Breeding Season Timing
Toads typically breed in the spring or early summer when temperatures warm up and rainfall increases. The exact timing of the breeding season depends on the species and geographic location, but it generally coincides with optimal conditions for eggs and tadpoles to develop.
For example, in many parts of the United States, American toads begin congregating at breeding ponds in March or April. By late spring and early summer, breeding activity declines as ponds start to dry up.
Toads are remarkably in tune with environmental cues like temperature and moisture to initiate breeding at the right moment each year.
Amplexus Mating Position
To mate, male toads climb onto the back of larger female toads and cling tightly to grasp them in what’s called amplexus. The male clings for hours, days or even weeks waiting for the female to release her eggs.
This maximizes his chances of fertilizing the eggs externally as the female lays the long, jelly-like strings. Sometimes several eager males will mount the same female! Females lay thousands to tens of thousands of eggs during breeding season, so it’s important for the persistent males to hang on tight.
The amplexus mating position may look awkward, but it has evolved to help facilitate external fertilization in toads and frogs.
Aquatic Egg Deposition
Nearly all toads deposit their eggs in water, even though adults are primarily terrestrial. Why? There are a few reasons:
- Eggs are vulnerable to drying out on land but are protected from desiccation in water.
- Tadpoles that hatch from the eggs require water to swim, feed, and undergo metamorphosis into baby toads.
- Water offers some protection from potential egg predators.
Different toad species lay eggs in various freshwater habitats like marshes, ponds, puddles, and slow moving streams or rivers. American toads and Fowler’s toads, for example, often breed in shallow, temporary woodland ponds that dry up later in the summer after tadpoles transform into young toads.
In rare cases, some toad species have adapted to reproduce on land. The Australian cane toad notably lays eggs on moist terrestrial substrates near water. But aquatic reproduction remains the norm for the vast majority of toad species worldwide.
Exceptions – Toads That Can Reproduce on Land
Moist Terrestrial Environments
While most toads lay their eggs in water, some species have adapted to reproduce in moist terrestrial environments. These adaptations allow them to take advantage of resources on land while still providing the moisture needed for their vulnerable eggs and tadpoles.
One example is the Puerto Rican crested toad (Peltophryne lemur). The female lays her eggs in humid burrows or under damp rocks and vegetation. She then remains with the eggs, guarding them from predators and keeping them moist by releasing urine.
Once the tadpoles hatch, they complete their development in small temporary rain pools formed on land.
Another terrestrial breeding toad is the green toad (Pseudepidalea viridis) of Europe. Females deposit eggs in shallow self-made burrows in soil. The tadpoles are well-adapted to complete metamorphosis in these confined terrestrial sites, aided by the highly gelatinous nature of the eggs which prevents desiccation.
By reproducing on land, these toads can take advantage of food sources unavailable in ponds and avoid aquatic predators. Their adaptations allow them to bypass bodies of water entirely in their life cycle!
Foam Nests
Some tropical toads in the family Rhinophrynidae build foam nests on land to protect their eggs and young. Females beat air into secretions to make a bubbly foam, within which they deposit eggs. The foam helps retain moisture while concealing and protecting the vulnerable embryos.
A well-known example is the Surinam toad (Pipa pipa) of South America. After mating, the female’s back becomes covered in small protrusions. She releases her eggs onto these spots on land, and the male fertilizes them. The female then oozes a foamy secretion over them, encasing each egg individually.
The foam hardens into a protective casing.
Over the next few weeks, the eggs hatch into tadpoles right within the foam nest. The female even distributes blood vessels over the nest surface so the enclosed tadpoles can receive oxygen and nutrition. After metamorphosis, the baby toads emerge from the nest fully formed.
Foam nests are an ingenious strategy that allows toads to take reproduction entirely out of water. It liberates them from reliance on ponds, maximizing available breeding spots.
Development and Metamorphosis of Toad Tadpoles
External Gills Form
After hatching from the egg, the toad tadpole is equipped with external gills that allow it to breathe underwater (1). These feathery gills are located on either side of the tadpole’s head and neck, absorbing oxygen from the water (2).
As the tadpole grows over the next few weeks, the gills eventually shrivel up and disappear as the lungs develop for breathing air (3). It’s amazing to witness this transition from aquatic to terrestrial living!
Front and Hind Limbs Grow
The next major step in a toad tadpole’s development is the sprouting of limbs! Around 2-3 weeks after hatching, tiny stubs form that will become the front legs (4). Then, after about 6 weeks, the hind legs begin to emerge (5).
It’s incredible to see these tiny leg buds slowly transform into the large, muscular legs of the adult toad over just a few weeks. As the legs grow, the tadpole becomes less suited to an aquatic life and more ready for land.
I love watching them test out hopping and walking in the late stages of development – they look kinda funny as they figure it out!
Tail Gets Absorbed
As the tadpole approaches the end of its metamorphosis into an adult toad, the next big change is what happens to its tail. Over a period of about 2 weeks, the tadpole’s tail shrinks and is reabsorbed into the body (6).
This is an amazing feat of development, as cells break down and reuse this entire structure. Finally, once the tail is gone, the toad is ready to venture out onto land! It has been a remarkable transformation over just a few short weeks.
From an aquatic creature with gills and a large tail, to a land-roaming toad with lungs and strong legs for hopping – nature sure is incredible!
It’s fascinating to observe toads lay their eggs on land near water, only for the tadpoles to then spend the first part of their lives fully aquatic. And the metamorphosis the tadpoles go through, developing those amazing adaptations for both water and land living, is just remarkable.
I could watch their growth and changes for hours!
Conclusion
In summary, while most toad species do require water for breeding and egg-laying, some toads have adapted the ability to reproduce successfully in damp terrestrial areas. Their eggs and tadpoles have evolved to withstand drier conditions through provisions like protective foam nests and accelerated development.
So next time you come across a mass of unknown eggs, consider they could belong to an innovative land-breeding toad!
