If you're looking for anime similar to Monmon the Water Spider, you might like these titles.
Both series are mute series (in other words: no spoken words) and are about unconventional characters going on an unconventional adventure. The story is fully told with the mere use of the visual medium and have a certain degree of iyashiekei (or therapeuthic / feelgood feeling) to them.
Both Mizugumo Monmon and Paulette no Isu tell us a story without using an dialogue at all. They are also rather cutely drawn and tell us a nice and calming story.
Just before dawn, Boro the Caterpillar hatched from an egg among patches of scrub grass. Looking around for the first time in fascination, he noticed the brilliance of the morning sun and a deliciousness in the air. As the sun lights up the grove, the borogiku (groundsel) leaves began to photosynthesize. "The air and water taste great!" Boro stepped out into the world of caterpillars' friends and foes.
Arichan the Ant finds a violin in a sandbox and keeps it. However, realizing how important it is to its owner, he returns it to her.
A group of elementary school children play in their classroom, imagining that they are on a boat in the ocean. This fantasy becomes reality, and soon all the students find themselves stranded in the deep blue sea, looking for their own Moby Dick. Some of the kids want to harpoon the whale, others want to take its picture, and many of the kids are afraid and just want to return home.
A boy named Yuji and his friend Gick, a rabbit, find a walking stick. To decide which of them will keep it, they try a foot race, a long jump and sumo wrestling, but each ends up in a tie. Out of ideas, the children go to Gick's Granny for help. Granny tells the children to go treasure hunting. Who will be the winner?
The puppy Koro rushes out of the house chasing Sawako leaving for school, but Koro gets lost. In unfamiliar places, Koro is nearly run over by a car, threatened by an alley cat... For little Koro, everything he encounters outside is new and a big adventure. Meanwhile, Sawako comes home to learn that Koro is gone. She frantically tries to find him.
One day, a boy who separated from his mother's hand is deprived of his fingers. When mother's love shows another side, his fingers become a larva and part from his hand. The house stands as concealed a relationship between the two from anyone. How does the boy who is deprived of his finger grow up?