Most Numerous Organisms in North America

By estimated individual count, the ranking is:

1. Bacteria – ~10³⁰ cells (soil, water, air, hosts). Dominant by orders of magnitude.
2. Insects – ~10¹⁸ individuals (100 quintillion). Arthropods dominate animal biomass.
3. Trees – ~1.3 trillion (recent NASA/Forest Service estimates).
4. Other: Nematodes, fungi, protists, viruses exceed all above in abundance but are less often counted as "organisms" in casual comparisons.

Why Bacteria Win

A single gram of soil contains ~10⁹ bacterial cells; North America's land area (2.4×10¹³ m²) implies astronomical totals.

Ecological Roles

• Bacteria: nutrient cycling, decomposition, nitrogen fixation, human microbiome.
• Insects: pollination, decomposition, food webs, pests.
• Trees: carbon sequestration, oxygen, habitat, timber.

Numbers are estimates; methodology varies. But bacteria outnumber everything else by ~12 orders of magnitude.