(CNN) -- Color-changing frogs, the world's longest stick insect and a slug that shoots "love darts" are among the biological "treasure" discovered by scientists in the lush green heart of Borneo.

Scientists have found 123 new species of animals, insects and plants on the South East Asian island since the three governments that control the land signed a pact to safeguard its future in 2007.

The new species are on a list released Thursday by the World Wildlife Fund (WWF) to mark Earth Day and to raise awareness of the value of protecting areas rich in biodiversity.

"You have some iconic small species which are very interesting to talk about but perhaps it's the plants that are tremendously important in terms of potential future cures," said David Norman, director of campaigns for the WWF.

"About half of all synthetic drugs have a natural origin -- these are commercial drugs based on plants and sometimes animals. So we can't afford to lose species," he said.

The number of new plant species discovered in Borneo in the last three years outnumbers all the other categories combined. Sixty-seven new plants have been found, along with 29 invertebrates, 17 new species of fish, one bird, five amphibians and five reptiles. The WWF describes the region as a "global treasure teeming with unique and extraordinary life."

Some of the more unusual amphibians found there include color-changing frogs, which also fly.

Males of the species (Rhacophorus penanorum) are just 3.5 centimeters long and their skin changes from bright green during the night to brown during the day. They can be found living in trees in the Tapin Valley within the Gunung Mulu National Park in Sarawak. Their fully-webbed feet allow them to glide for up to 15 meters from tree branch to tree branch.

The tail of the long-tailed slug (Ibycus rachelae) is three-times the length of its head, allowing it to curl up to sleep. More unusually, when it mates the slug fires a so-called "love dart" made of calcium carbonate that injects a hormone into its prospective partner to increase the chances of reproduction.

The world's longest-stick insect (Phobaeticus chani) is more than half a meter long and lives high up in the rainforest canopy. "Only three specimens have ever been discovered. It's quite extraordinary that it's been there for so long -- you wouldn't miss it if it landed on you," Norman said.

The rate of the discovery of new species has increased since 2007 when the governments of Indonesia, Malaysia and Brunei signed an agreement to conserve the area.

The agreement covers a 220,000 square kilometre tract of land that straddles all three countries which is known as the Heart of Borneo.

"This not just a nature reserve. There are lots of people who live there. Farming goes on there. There is eco-tourism. These are all things that must continue. The point is to ensure that the value of the forest standing is much greater than the value of it being cut down," Norman said.

The WWF says the Heart of Borneo Declaration has worked to conserve the environment by exerting pressure on governments, developers and industry to adapt their plans to minimize their impact on the land.

It credits the agreement with preventing the destruction of two million hectares of rainforest to create the world's largest palm oil plantation. Plans to build a road through the middle of the region in 2007 were also shelved for environmental reasons.

"About half of all the land in the heart of Borneo lies in private hands. It's so remote you can't possibly enforce this, so this is very much about negotiating agreements. Whenever there is a new proposal for a new road or a new farm or a new plantation or a new mine, it is worked through in the context of the agreement that was signed in 2007," Norman said.

Meanwhile, scientists are still busy surveying the tangled mass of plants, animals and insects that thrive in the hot, humid conditions of the Borneo rainforest. The WWF says it is impossible to predict how many more new species will be found.

"It is so difficult to know how many species there are on the planet. Scientists sometimes estimate maybe there are 10 million species in total out there and we've only described 1.7 million of them so far," Norman said.