Hatching frog eggs and raising larval amphibians to metamorphosis can be a fascinating and educational experience for children and adults alike, and can add immensely to the enjoyment of these creatures. If you'd like to give this a try, the following guidelines will help.
Objectives: Students will learn about the metamorphic changes frogs undergo in their lifecycle. Students will understand the habitat needs of frogs.
1. Have students collect eggs and larvae.
To collect frogs in Wisconsin, you need a valid fishing license or a small game license. You don't need a license to collect frog eggs. Frog season opens on the Saturday nearest May 1 and runs through December 31 each year. Each person may collect up to one clutch of eggs, but once they transform, you are only allowed to retain up to five individuals. The balance of any eggs, tadpoles or transformed individuals must be released ONLY to the pond where the eggs originated, and these must show no signs of being sick or diseased. You will find a short list of rules in the "Spearing and Netting Regulations" pamphlet available at DNR offices and other license outlets. Document where the eggs are collected from with a small flag or by marking the exact location on a map of the area. This information will be needed to release the amphibians to the same location once they are grown.
Never remove eggs or larvae from public areas such as parks, refuges, or conservation areas. Ask permission before removing specimens from private land. Also make sure you are not collecting eggs or tadpoles of the protected Blanchard's cricket frog (see illustration and check out the guide to frog egg identification and metamorphic timing). Only collect as many as your bowl or aquarium can hold without over-crowding (1 gal. per 2 tadpoles).
Please Note:Frogs are selective and only breed when temperatures in the air and water are just right. To make things more fun, each frog's eggs look different and hatch at different times. Be sure to take a look at this guide to frog egg identification and metamorphic timing to help you with this activity.
Ponds, small lakes, and creeks are ideal places to find amphibian eggs and catch tadpoles. Have students use small dip nets or jars to collect eggs and larvae and transport them to the classroom in clean jars, plastic bags or plastic containers. Have students also take a temperature reading of the water. Then have them put the eggs or larvae in an insulated bag or cooler in order to maintain the approximate temperature of the water. Take an extra container of water from the water body where the specimens were collected to place in the aquarium.
2. Have students set up the "habitat."
Eggs and tadpoles can be kept in a large, flat pan, fish bowl, aquarium, or a large glass jar. Set up their new home ahead of time.
Use water from the pond where you collect the eggs or larvae to give them a head start. Chlorinated tap water destroys bacteria and algae and it can harm or kill amphibian eggs and larvae. If you need to use tap water, treat it with a dechlorinator. You can buy it at a pet store. Or, let a jug of water stand a few days with the lid off so the chlorine can dissipate. Provide at least 1 gallon of water for every two tadpoles to prevent over-crowding, and use an air stone and air pump to provide a constant stream of fine bubbles. It is not necessary to provide sand or gravel. Eggs found in submerged habitats should be kept submerged, and those found floating should be allowed to float.
3. Have students feed the frog and toad tadpoles.
Discuss the diet of tadpoles and frogs throughout their lifecycle. Ask the students to think of ways they can provide these animals with the specific foods they need. Have students devise a feeding plan and schedule.
Note about food:
Note about food:Tadpoles usually eat algae and other minute plant matter, but this may be hard to get in sufficient quantities at home or school. Finely ground commercial goldfish food, a commercial Trout Chow, or algae from another aquarium should be fed twice daily. As a substitute you can boil and cool 2 tablespoons of fresh spinach or lettuce (not cabbage). If available, crush rabbit food pellets and feed them to tadpoles as a dietary supplement. Small flakes of hard-boiled egg yolk can be added twice a week as a protein supplement. Feed only what the tadpoles can eat in a hour to avoid fouling the water. Remove any uneaten food promptly.
As tadpoles become frogs, their diet changes from eating plants to feeding exclusively on live animals such as insects and small crustaceans. It's a real challenge to find enough food to maintain most juvenile frogs for very long. Tiny meal worms or aphids from infested houseplants are your best bet, but you might want to simply release the little frogs to ensure their survival.
4. Have students record transformation to adult stages.
Tadpoles undergo three remarkable changes that are easy to observe. First, they grow legs -- back legs first; front legs last. Second, they slowly lose their tails. As the front legs grow, the tadpoles will no longer eat. The tail shrinks as the tissue is reabsorbed as food by the tadpole. Finally, the tadpole switches from breathing with gills to breathing with lungs after it grows legs. Have students record daily observations and document how long it takes for each stage to occur.
Once the tadpoles' hind legs appear, you need to rework the landscape in their container. Discuss with your students the habitat needs of tadpoles versus frogs. Create a habitat design for the tank. Be sure that students provide a gently sloping place where the froglets can crawl out of the water. When the froglets are ready to leave the water, they must be able to do so quickly, or they may drown. A small pile of rocks is fine. Driftwood also works, but avoid all types of treated lumber.
5. Have students return amphibians to their natural habitat.
After students complete their observations, have them release the critters back into the wild where they were originally collected as eggs or larvae. Have students find the flags used to mark the location of collection or follow the property map they marked when collecting eggs. Do this before the end of September so the froglets have time to find places to hibernate for the winter. Discuss how some amphibians migrate to find the habitat they need during the winter, and what type of habitat each one needs during different times of the year. Discuss with students how amphibians survive during the winter.
Note:Do not release animals that were not collected in Wisconsin or are not naturally found here. It's against the law for a good reason. Introducing species that are not found here could jeopardize native species; foreign genetics, diseases and/or parasites can pose severe problems. Also, never release an animal obtained from a pet store or biological supply company.
A tragic example occurred in Calaveras County, California. The celebrated jumping frog of this locale was eaten not only by gold miners in the 19th century, but unfortunately they were completely eaten into extinction by the eastern bullfrogs that were brought West and released for food and hunting in the 20th century. This tragedy was avoidable and serves as a good teaching tool of how introduced species can affect native amphibians.