A few species, notably Spiroplasma mirum, grow well at 37 °C (human body temperature), and cause cataracts and neurological damage in suckling mice.

There is some disputed evidence for the role of spiroplasmas in the etiology of transmissible spongiform encephalopathies (TSEs), due primarily to the work of Frank Bastian, summarized below.

[3] Bastian et al. (2007) have responded to this challenge with the isolation of a spiroplasma species from scrapie-infected tissue, grown it in cell-free culture, and demonstrated its infectivity in ruminants.

[5][6] The mechanism through which S. poulsonii attacks nematodes and parasitic wasps relies on the presence of toxins called ribosome-inactivating proteins (RIPs), similar to Sarcin or Ricin.

[15] In an interview with the Global Health Institute, Dr. Toshiyuki Harumoto said this discovery is the first example of a bacterial effector protein that affects host cellular machinery in a sex-specific manner, and the first endosymbiont factor identified to explain the cause of male-killing.

[16] Beyond Drosophila, Spiroplasma of the ixodetis, apis, chrysopicola, citri, mirum, and poulsonii clades are found in many insects and arthropods, including ticks, spiders, bees, ants, beetles, and butterflies.

[17][18][1][19] Male-killing is also found in the Spiroplasma of the ladybird beetles Adalia bipunctata [20] and Harmonia axyridis [21], the plain tiger butterfly, the lacewing Mallada desjadinisi,[22] and the pea aphid Acyrthosiphum pisum.

Spiroplasma kunkelii represents a major economic risk, as corn production in the United States is an industry worth over $50 billion.

[29] Spiroplasma genomes are commonly extremely AT rich, can contain a variety of prophage (viral) elements, and also plasmids.CRISPR defences are found in some members of the genus.