The purest soil that you can get is the soil from the termitaria. Termites are very common in the forests of Sal, Shorea robusta or in other tropical and temperate forests. In healthy forests, they build a huge number of termitaria, one at almost every 10 sq.m. I live about 1hr away from such forests so I always have a supply of its pure soil in my puja room. If you come across such termitaria, keep a small block of this soil in your house. When harvesting the soil, choose a block which seems to be abandoned by the termites and sincerely thank the termites for this gift. This soil is a living energy, auspicious, pure and is used for several pujas. It has the highest capacity to absorb mantra etc recited over it and has the highest ability to reflect their power back to you. It is a solid stable energy and the results of this puja will give similarly solid results which will act as a foundation for several auspicious things in life.
The most common use of this soil is in making a Parthiv Shivlingam for pujas. As the lingam is created using soil, Pruthvi, it is called Parthiv. Shiv pujas performed on such a lingam made of generate very high levels of power. Try to perform such a puja on every monthly Shivratri or at least the Mahashivratri night or on the Mondays of Shravan month. The best time to perform such pujas is the 4th prahar of the night.
This soil is also to create a moorti of the Naag on Naag Panchami day for pujas. Also use this soil to create a moorti of Hartalika Devi for her pujas on Bhadrapad Shukla Trutiya. Or to create a moorti of the Devi for the Mangala Gauri pujas on the Tuesdays of Shravan month. This soil is the ideal material to create Ganapati moortis for Bhadrapad Shukla Chaturthi. During Diwali, some people do pujas of Devi Laxmi moorti created out of soil.
In case you do any of these pujas do use the termitoria soil to make the moortis, you will feel the difference immediately. Use turmeric, vermillion, saffron and bhasma to add color to the moorti. Unfortunately we have switched to Plaster of Paris for making such moortis eg Ganapati Puja moortis are all made with this non-living chemical material. It has no power to absorb the mantra pujas being done on it and no ability to reflect it back to the devotees. Avoid using this material in your moortis for pujas. They are very beautiful are of little use in the energy sense.
After doing pujas this moorti or the lingam made of termitaria soil is put in flowing water, ie its actual Visarjan, is done. This ensures that the residual energy of the mantra is released into the water. Water is the repository, ie the collective memory of everything that gets deposited into it. So when such a Parthiv moorti is deposited into water, its auspiciousness, the power of the mantra recited on it and the pure intentions of the devotees all merge into the waters of that area, increasing the overall auspiciousness of that water and eventually the land. We eat food produced from this land and drink water from these water bodies. Returning the energy back to the soil and water in gratitude is inbuilt in our way of life.
And since we are on the subject of insects and the purity of their homes, one Guru once told me why we put out sugar for black ants. It is not only as a gesture of gratitude but wherever there are black ants, Sakshat Dharma is present in that place. Black ants are the embodiment of Dharma. You can test this. If you live in an area where people live according to Dharma you will find these small sized black ant-hills scattered around the place. And in localities where people have adopted Adharma as their way of life, there will be no black ant hills. So here is one more practice which you can adopt if you feel like it, putting out some sugar for black ants once in a while.
In fact the Naag panchami puja is supposed to be done on site, ie at such a black ant hill or the termitaria. You are supposed to go to the wild / forest areas to perform these mantra for the Naag.
There are no superstitions in Sanatan Dharma, just a heightened awareness of energy dynamics and the intentions powering us all. This is why this is called the Eternal Foundation and everyone must try to stick to it as much as possible.