Camels and alpacas naturally produce them too!
Oxford University researchers hope the antibodies - known as nanobodies due to their small size - could eventually be developed as a treatment for patients with severe Covid-19.
The immune system produces antibodies when it is being attacked, or in response to infections.
Llamas, camels and alpacas naturally produce quantities of small antibodies with a simpler structure, that can be turned into nanobodies.
The team from the Rosalind Franklin Institute, Oxford University, Didcot's Diamond Light Source and Public Health England engineered their new nanobodies using a collection of antibodies taken from llama blood cells.
They found that the nanobodies bind tightly to the spike protein of the Sars-CoV-2 virus, blocking it from entering human cells and stopping infection.
In the study published in Nature Structural and Molecular Biology, the team also identified that the nanobodies bind to the spike protein in a new and different way to other antibodies already discovered.
James Naismith, director of The Rosalind Franklin Institute and professor of structural biology at Oxford, said: "These nanobodies have the potential to be used in a similar way to convalescent serum, effectively stopping progression of the virus in patients who are ill.
"We were able to combine one of the nanobodies with a human antibody and show the combination was even more powerful than either alone.
"Combinations are particularly useful since the virus has to change multiple things at the same time to escape - this is very hard for the virus to do.
"The nanobodies also have potential as a powerful diagnostic."
Oxford Professor Ray Owens - who leads the nanobody programme at the Franklin, said the researchers are hopeful they can push the breakthrough on into pre-clinical trials.
Professor David Stuart, from Diamond Light Source said: "The electron microscopy structures showed us that the three nanobodies can bind to the virus spike, essentially covering up the portions that the virus uses to enter human cells."
Researchers started from a lab-based library of llama antibodies, and are now screening antibodies from Fifi, one of the 'Franklin llamas' based at the University of Reading, taken after she was immunised with harmless purified virus proteins.
The team is looking at preliminary results which show that Fifi's immune system has produced different antibodies from those already identified, which will enable cocktails of nanobodies to be tested against the virus.