Ground beetles have glands at the end of the abdomen that produce defensive, foul tasting and caustic secretions. I must quote here an incident involving ground beetles described by Charles Darwin
I must tell you what happened to me on the banks of the Cam in my early entomological days; under a piece of bark I found two carabi (I forget which) & caught one in each hand, when lo & behold I saw a sacred Panagæus crux major; I could not bear to give up either of my Carabi, & to lose Panagæus was out of the question, so that in despair I gently seized one of the carabi between my teeth, when to my unspeakable disgust & pain the little inconsiderate beast squirted his acid down my throat & I lost both Carabi & Panagæus!The pains beetle collectors went through to capture priced ground beetles! You can admire the handsome Crucifix Ground Beetle (Panagaeus cruxmajor), also known as 'Darwin's lost beetle' here. Unfortunately, due to collecting and habitat degradation, this species, formerly widespread, is now just know from three populations in the UK.
But back to my beetle, I managed to take some shots of the individual scurrying off for cover on the soil, and then I decided to capture it and give it a session in the white bowl. I think the following two photos show the pros and cons of the natural versus the white background.
Pterostichus madidus, 12 May 2012
Charles Darwin letter to Leonard Jenyns in the Darwin Correspondence project.Crucifix ground beetle (Panagaeus cruxmajor) UKBAP plan.