Professor James Marden of Pennsylvania State College has been studying Libellula pulchella, the twelve spotted, skimmer dragonfly.

He says that they are combative and among the fittest animals in the world. The males are extremely territorial and will engage in aerial fights until one of the chases the other off.

However, some of the males seen to glide by as though they are just passing through. These males are fat and very ill. They have blood sugar concentrations that are double what it should be with fat collected in their tissues instead of being utilized to power their very strong wings. They are in an insulin-resistant state, similar to what is found in human patients with type 2 diabetes.  

Professor Marden decided to dissect some of these obese dragonflies and found that their diabetic-like state and obesity was caused by large, white, plump gregarines, protozoans from the family that causes malaria and cryptosporidiosis (a condition caused by a parasite of the small intestine that has been recognized as a worldwide cause of diarrhea in all age groups.) in humans and in these dragonflies’ guts.

The parasite caused an inflammatory response that interfered with their ability to metabolize fat. They were duller, slower, and components of their metabolism were changed. It also caused the chronic activation of a signaling molecule involved in immune and stress response, p38 MAP kinase, the same molecule in humans implicated in insulin resistance that can lead to type 2 diabetes.

Professor Marden found that the parasite was non-invasive and did not chew or bore in to the gut walls. The inflammatory effect was caused by substances the gregarines secreted or excreted. Furthermore, he found that, if uninfected dragonflies were to drink water containing trace amounts of the gregarine secretions or excretions, their blood sugar levels were abnormal as well.

In conclusion, it is interesting how gut flora can influence organisms’ ability to metabolize food and control weight. Research done on gut flora and probiotics has merit when it comes to addressing the issue of the obesity epidemic seen in humans and other organisms.    

To read more, check out Dr. Marden’s website: