Nature Diary
Symbiosis
You must have seen white birds sitting on cows grazing in the fields. These birds are in fact called cattle egrets since they are so closely seen with cattle. Theirs is a very strong relationship: the bird eats the small ticks and other insects on the cow's skin. This helps the cow to get rid of these harmful ticks that bite it and suck their blood. This kind of relationship between different species is called symbiosis. In particular, it is called mutualism, since both the species benefit from this relationship. That is because the cattle egrets eat the ticks from the cattle's backs and get nutrition from it. As the cattle walk, they also disturb small flies and insects, and the egret feast on them as well. Birds can also have similar mutually beneficial relationships with plants. Frugivorous birds are ones that eat fruit. They then spit out the seeds. This helps plants by dispersing their seeds, sometimes to far away places. On the other hand, the birds get nutrition from the fruit.
Another example of mutualism is that of clownfish, made famous by the movie "Finding Nemo". These fish dwell among the tentacles of sea anemones. The fish protects the anemone from anemone-eating fish. In turn, the anemone uses its stinging tentales to protect the clownfish from its predators. The relationship has developed in such a way that the clownfish excretes a special mucus which prevents it from getting stung by these same tentacles!

There are other kinds of symbiosis that may not be mutually helpful. In commencalism, only one of the members of the relationship is benefitted, although the other member is not harmed in any way. For example, spiders build their webs on plants. It helps them anchor the web, while the plant is not harmed in any way.
The third form of symbiosis is called parasitism. Here, the parasite benefits from the relationship, but the host is actually harmed in the process. One of the most common examples is that of the plasmodium parasite which causes malaria. They are carried by mosquitoes that are called the vectors. Female mosquitoes need blood to multiply (to lay eggs). Male mosquitoes do not bite. Female mosquitoes can get the blood from humans or animals. While biting us, the moquito injects the parasite from herself into our bodies. If the person is already infected, the mosquito takes up the malaria parasite along with blood, from our bodies. Hence the cycle continues.
We also have many parasites like tape worms in our intestines, that have hooks that attach themselves to the wall of the intestine. They infect us through contaminated food, and can live for years comfortably in our intestine, but cause us many health problems. Parasitism is a very successful mode of life; about 40% of all animal species are parasites! Unlike predators which kill and eat their prey at once, the parasites live in their hosts for a long time.
Credit: Pictures from Wikimedia and https://vasundharagautam.com/posts/2021-12-31-bird-facts/